Tracheal Intubation - Clinical Tree

Intubation is often the pivotal procedure in the emergency management of critically ill patients. There are several new devices that can improve the likelihood of successful intubation, and it is important to put the intubation procedure in perspective, understanding that intubation is just one part of airway management. The primary objective of airway management is to maintain adequate ventilation and oxygenation, and intubation only allows ventilation and oxygenation after the procedure is completed, not during the procedure. It is critical to have good basic airway management skills (see Chapter 3 ). It is also important to use intubation techniques that have a high likelihood of first pass success, to have the wisdom to recognize when a given approach has failed, and to quickly move to a different technique. Use of an emergency airway algorithm can help providers make difficult decisions in a timely manner (see later section on Emergency Airway Algorithm ).

This chapter describes nearly every possible means of tracheal intubation, with emphasis on widely used techniques. The most common means of intubation in the emergency setting is rapid-sequence intubation (RSI), and this approach must be considered very carefully. If a difficult intubation is anticipated, awake intubation may be preferred. Although flexible endoscopic devices are commonly used, with good topical anesthesia, nearly any intubating technique can be used for awake intubation. Because many difficult airways cannot be predicted, it is essential to have a well-defined backup plan and appropriate resources. The intubating laryngeal mask airway (LMA Fastrach, Teleflex, Inc, Wayne, PA) is an ideal backup device for failed RSI because it provides ventilation and oxygenation and facilitates tracheal intubation in a high percentage of patients with failed RSI.

General Approach to Emergency Intubation

Preplanning is the key to successful emergency airway management. Providers should follow a clear, preconceived, practiced airway algorithm that uses readily available and familiar equipment and techniques. When encountering a difficult airway, it is more important to be comfortable with a few well-proven devices and techniques than to try new or unfamiliar devices. It is important to know when to abandon one approach and move on to the next. No single approach is mandated. The best technique is the one chosen by the clinician at the bedside based on one's individual experience and expertise given the specific clinical scenario.

A critical aspect of preparation is making sure that all essential equipment required to perform the airway maneuvers is immediately available and within easy access. This may be accomplished by wall-mounting essential equipment in the emergency department (ED) resuscitation room. Alternatively, equipment can be placed in dedicated adult and pediatric airway carts or tackle boxes in an open, organized, and labeled manner, with the carts and boxes checked and stocked regularly ( Fig. 4.1 ). Essential equipment that is seldom used but is potentially lifesaving should be clearly identified and placed in an easily accessible location such as a dedicated difficult airway cart. The importance of this concept cannot be overstated. Technical expertise cannot substitute for the lack of essential equipment. In airway management, failure has ominous consequences. Mental, physical, and equipment preparation maximizes the chance of success.

Figure 4.1, A, Adult airway cart. Equipment and materials are visible, labeled, and accessible. B, Labeling is especially important because it lets you know what is missing.

Airway Anatomy

An understanding of airway anatomy and its terminology is requisite for any discussion of airway management procedures ( Fig. 4.2 ). The following terms are used frequently in this chapter:

Pharynx : the upper part of the throat posterior to the nasal cavity, mouth, and larynx
- 1.
  Nasopharynx : base of the skull to the soft palate
- 2.
  Oropharynx : soft palate to the epiglottis
- 3.
  Hypopharynx : epiglottis to the cricoid ring (posteriorly), including the piriform sinus/recess/fossa
Piriform sinus/recess/fossa : the pockets on both sides of the laryngeal inlet separated from the larynx by the aryepiglottic folds
Larynx : the anterior structures of the throat (commonly called the voice box) from the tip of the epiglottis to the inferior border of the cricoid cartilage, including the laryngeal inlet
Laryngeal inlet : the opening to the larynx bounded anterosuperiorly by the epiglottis, laterally by the aryepiglottic folds, and posteriorly by the arytenoid cartilage
Arytenoid/posterior cartilage : the posterior aspect of the laryngeal inlet separating the glottis (anterior) from the esophagus (posterior)
- 1.
  Corniculate cartilage : the medial portion of the arytenoid/posterior cartilage
- 2.
  Cuneiform cartilage : the lateral prominence of the arytenoid/posterior cartilage
- 3.
  Interarytenoid notch : the notch between the posterior cartilage
Glottis : the vocal apparatus, including the true and false cords and the glottic opening
Vallecula : the space between the base of the tongue and the epiglottis
Hyoepiglottic ligament : anterior midline ligament connecting the epiglottis to the hyoid bone

Figure 4.2, A, Anatomy of the upper airway. B, View of the larynx, epiglottis, and vocal cords seen with a laryngoscope. The key to a successful intubation is identification of the vocal cords.

Preparation

Intubation is best accomplished with two operators, one to perform the intubation and the other to handle equipment, help with positioning, observe the patient and monitor, and keep track of time. Unfortunately, the ideal scenario and adequate time for preparation are not always available to the clinician, who has to make calculated adjustments based on the situation at hand. Before intubating, it is preferable to take the following steps in chronologic order: (1) attach the necessary monitoring devices and administer oxygen, (2) establish intravenous access, (3) draw up essential medications and label them if time permits, (4) confirm that the intubation equipment is available and functioning, (5) reassess oxygenation and maximize preoxygenation, (6) position the patient correctly, and (7) make sure that all team members are aware of the primary procedural approach and the most likely backup plan. In the haste of the moment, it is a common error to forget to preoxygenate or to position the patient optimally. Simple omissions, such as failing to restrain the patient's hands or remove the patient's dentures or misplacing the suction tip, can seriously hamper the success of the procedure. Utilize universal precautions by wearing gloves, a gown, and eye and mouth protection.

The concept of using checklists to decrease medical errors and improve patient care has grown since a landmark article demonstrated decreased complications and mortality in surgical patients when checklists were utilized. Timely and successful tracheal intubation, while minimizing hypoxemia and other complications, is paramount when caring for ill and injured patients who require intubation. Pre-intubation checklists can reduce cognitive load for the intubating physician by creating a framework for approaching all emergency intubations. Checklists prompt clinicians to verify that all necessary equipment is available and functioning, to perform a standardized airway assessment, to execute optimal preoxygenation, and to develop an airway plan with patient-specific backups. The use of pre-intubation checklists has been shown to reduce peri-intubation complications in trauma patients. Example checklists are seen in Box 4.1 .

Box 4.1

Preintubation Checklists

Pre-arrival

1.
Bag mask ventilation setup with oxygen running at >15 L/min
2.
Suction connected and running
3.
Laryngoscope functioning and ready
4.
Ready an endotracheal tube: check cuff, insert stylet, and have a “straight to cuff” shape with a 35-degree distal bend
5.
Back-up devices such as laryngeal mask airway or King LT airway available and ready
6.
Cricothyrotomy set located
7.
End-tidal CO ₂ detector ready

Pre-intubation

1.
Assess the airway: open mouth, examine neck mobility, palpate anterior neck
2.
Decide best approach: awake, sedated, or RSI
3.
Communicate intubation medication orders to nurses, including post-intubation medications
4.
Optimally position patient
5.
Preoxygenate patient (usually with face mask oxygen at 60 L/min)
6.
Apply nasal cannula at 10–15 L/min in preparation for apneic oxygenation
7.
Discuss airway plan with entire team
8.
Ensure functioning pulse oximeter
9.
Ensure patient intravenous catheter
10.
Ensure assistants are ready (nurses, respiratory therapists)

RSI, Rapid-sequence intubation.

Preoxygenation

Preoxygenation is one the most important aspects of emergency airway management. The goal of preoxygenation is to replace all the nitrogen in the lungs with oxygen prior to the start of intubation attempts. This allows the lungs to act as an oxygen reservoir during the apneic period of RSI. This provides the intubator with additional time before the onset of hypoxemia, and significantly increases the chance for successful intubation on the first attempt. It is not enough to achieve a peripheral oxygen saturation (Sp o ₂ ) value of 100% prior to intubation, because an Sp o ₂ of 100% does not necessarily correspond with denitrogenation of the lungs; furthermore, partial pressure of arterial oxygen (Pa o ₂ ) at 100% Sp o ₂ can range from approximately 100 mm Hg to 600 mm Hg. Failure to preoxygenate before RSI is often a critical factor when a straightforward emergency airway becomes an unexpected airway problem. Those at greatest risk for rapid desaturation include obese, pregnant, critically ill, and pediatric patients; these populations will benefit most from optimal preoxygenation.

Preoxygenate by providing the maximal fraction of inspired oxygen (Fi o ₂ ) with a simple face mask or non-rebreather mask for 3 to 5 minutes before intubation. The type of mask is less important than the oxygen flow rate ; at very high flow rates the Fi o ₂ for any device usually exceeds 90%. At lower flow rates (< 30 L/min) the Fi o ₂ will not be high enough for adequate preoxygenation, so the oxygen flow rate should be at least 30 L/min. When using a standard oxygen flow meter this requires turning it up as high as possible, beyond the marked maximum of 15 L/min, to the “flush” rate. The flush rate is usually marked on each flowmeter and is typically greater than 40 L/min. Oxygen flowmeters that can measure up to 70 L/min, with flush rates up to 90 L/min, are available (see Fig. 3.7 in Chapter 3 ); however, a flush rate greater than 40 L/min is probably sufficient for maximal preoxygenation. Providing high flow oxygen washes out expired CO ₂ , fills the dead space of the nasopharynx and upper airway with oxygen, compensates for any leak between the mask and the patient to avoid entrainment of room air during inspiration, and may provide low levels (1 to 2 cm H ₂ O) of positive airway pressure. The importance of very high flow oxygen administration during preoxygenation cannot be overemphasized. If possible, instruct the patient to exhale maximally before beginning preoxygenation.

Alternatively, if it is not possible to perform preoxygenation for 3 to 5 minutes prior to intubation, instruct the patient to take eight vital capacity breaths while delivering very high flow oxygen, to provide nearly the same result. Many critically ill patients will not be able to take vital capacity breaths; therefore with time permitting, the preferred method is 3 to 5 minutes of tidal breathing.

Unlike face masks, bag-mask ventilation (BMV) requires proper equipment and good technique to achieve adequate preoxygenation. Bags without one-way valves for inhalation and exhalation will not function properly during spontaneous ventilation, and will provide only room air. Furthermore, unless flow rates are very high (>40 L/min), the mask must be sealed perfectly to the patient's face (see Chapter 3 for proper technique). If the seal is imperfect, room air will be entrained and Fi o ₂ will be close to that of room air. This is analogous to holding a mask above a patient's face, which likewise provides oxygen content near that of room air. In spontaneously breathing patients, face masks (with a very high flow rate) are the preferred oxygen delivery device for preoxygenation.

To augment oxygen delivery and prepare for apneic oxygenation (see next section), apply a nasal cannula (at 15 L/min) to the patient during preoxygenation, simultaneously with other preoxygenation efforts. High flow nasal cannula (see Chapter 3 for details), if available, may also improve preoxygenation, though this has never been studied in combination with a high-flow face mask.

The preferred position for preoxygenation is head elevation of 20 to 25 degrees. This position minimizes atelectasis, decreases the pressure of the abdominal contents against the diaphragm, and allows the patient to continue taking deep breaths. In both obese and non-obese adults this position has been demonstrated to be advantageous for preoxygenation. For patients with spinal immobilization, the bed can be placed in 25 degrees of reverse Trendelenburg (head up) to achieve the same effect.

If Sp o ₂ cannot be increased above 93% to 95% after optimal preoxygenation, the addition of positive pressure using noninvasive positive pressure ventilation (NPPV) or mask ventilation with a positive end-expiratory pressure valve may improve oxygenation prior to intubation attempts.

Sometimes patients who will benefit the most from preoxygenation are uncooperative because of delirium from hypoxia, hypercapnia, or other factors. Application of a face mask or NPPV may be difficult or impossible. These patients may benefit from careful sedation without suppression of respirations, allowing for oxygenation with a face mask or NPPV for 2 to 3 minutes before administration of a paralytic agent (also known as delayed sequence intubation ). Ketamine (1 to 1.5 mg/kg by slow intravenous push) has been suggested for this technique. Weingart and colleagues performed sedation for preoxygenation in 62 adults, and demonstrated an increase in Sp o ₂ for most patients without any adverse events. Because of the small sample size and because these patients were managed by experts in airway management and sedation, this technique is not necessarily generalizable to everyday clinical practice. If a patient is sedated for preoxygenation, the clinician should be vigilant for respiratory depression, apnea, and airway obstruction, and have all airway equipment available in case emergency control of the airway or breathing becomes necessary. In many cases, it may be safer to restrain the patient without sedation to facilitate preoxygenation.

Apneic Oxygenation During Intubation

Another method to delay desaturation during RSI is nasopharyngeal oxygen insufflation without ventilation, termed apneic oxygenation. Even in the absence of ventilation, oxygen is able to travel down the tracheobronchial tree to the alveoli and diffuse into the bloodstream, where it is consumed and converted into carbon dioxide. Because oxygen diffuses across the alveoli much more readily than carbon dioxide, because oxygen and carbon dioxide have differences in gas solubility in blood, and because of the high affinity of hemoglobin for oxygen, more oxygen leaves the alveoli than carbon dioxide enters. This creates a pressure gradient that causes oxygen to travel from the nasopharynx to the alveoli and into the bloodstream.

Studies have shown that providing oxygen therapy during apnea is much more beneficial than one might anticipate. Multiple studies conducted in the operating room, in normal and morbidly obese patients, have shown that nasopharyngeal oxygen insufflation results in a significant delay in desaturation after the onset of apnea, with many subjects never developing hypoxemia even after six minutes of apnea.

A 2016 randomized trial in an intensive care unit (ICU) found no difference in the oxygen saturation nadir between patients who received and did not receive apneic oxygenation during intubation. Because ED patients are often intubated within minutes of arrival despite limited history and sometimes limited preoxygenation, and because, contrary to ICU patients, ED patients generally have not been on supplemental oxygen for the several hours preceding intubation, the results of this study should not be generalized to ED care.

Perform apneic oxygenation with every tracheal intubation to decrease the chance of severe hypoxemia. Place a standard nasal cannula beneath the main preoxygenation device (face mask or bag-valve mask). If the patient is awake, limit the flow rate to 5 to 15 L/min during the preoxygenation phase because higher flow rates can be uncomfortable. If the patient is comatose or unresponsive, set the nasal cannula to 15 L/min or higher when initially placed. When the preoxygenation device is removed for intubation, keep the nasal cannula in place. During intubation attempts, set the nasal cannula to at least 15 L/min. It may be beneficial to turn the oxygen flowmeter up as high as possible because higher flow rates have been shown to provide higher Fi o ₂ . If there is nasal obstruction, place a nasopharyngeal airway in one or both nares to facilitate oxygen delivery to the posterior nasopharynx. To optimize gas flow past the upper airway, position the patient for tracheal intubation, and perform maneuvers to ensure upper airway patency (i.e., jaw thrust, head tilt/chin lift). Because conventional nasal cannula oxygen delivery is not humidified, apneic oxygenation at high flow rates will cause some desiccation of the nasopharynx, but this should not cause significant harm because of the short duration of this oxygen supplementation.

High-flow nasal cannula systems may be an even better method of apneic oxygenation, and have been shown in an ICU study to be superior to simple nasal cannula, though both groups had low rates of hypoxemia.

Assessing for a Difficult Airway

When trying to predict whether there will be difficulty during emergency intubation, it is important to understand that most of the literature on prediction of difficult laryngoscopy does not apply very well in the emergency setting. A study by Levitan and colleagues in 2004 showed that two-thirds of patients who were intubated in their ED via RSI could not be assessed with the most common difficult airway prediction tests (Mallampati scoring, measurement of thyromental distance, and neck mobility testing) because of altered mental status or cervical spine immobilization. Even in the best circumstances, only approximately half the cases of difficult laryngoscopy can be predicted. Many factors such as Mallampati scoring and measurement of the thyromental distance have not been found to accurately predict difficult laryngoscopy, especially in the emergency setting. Only obvious anatomic and pathologic abnormalities and a history of difficult intubation are accurate predictors of difficult laryngoscopy. The American Society of Anesthesiology Difficult Airway Guidelines state that “in patients with no gross upper airway pathology or anatomic anomaly, there is insufficient published evidence to evaluate the effect of a physical examination on predicting the presence of a difficult airway.” This does not mean that emergency providers should ignore factors that are known to be associated with difficult laryngoscopy, but these must be placed in perspective.

No examination finding alone can predict difficult laryngoscopy, and a combination of multiple factors makes difficulty more likely. The classic predictors of difficult intubation include a history of previous difficult intubation, prominent upper incisors, limited ability to extend at the atlanto-occipital joint, poor visibility of pharyngeal structures when the patient extends the tongue (Mallampati classification or the tongue-pharyngeal ratio) ( Fig. 4.3 A ), limited ability to open the mouth (suggested by a space less than three fingerbreadths between the upper and lower incisors), short thyromental distance (< 6 cm from the thyroid notch to the chin with the neck in extension) (see Fig. 4.3 B ), and a limited direct laryngoscopic view of the laryngeal inlet ( Fig. 4.4 ). A relatively new test is the upper lip bite test, which has been shown in some studies to be more accurate and specific than older tests. It is essentially a test of anterior mandibular mobility, and the less mobility the more difficult it is to intubate the patient. Upper lip bite criteria are as follows: class I, the lower incisors can bite the upper lip above the vermilion line; class II, the lower incisors can bite the upper lip below the vermilion line; and class III, the lower incisors cannot bite the upper lip.

Figure 4.3, A, The Mallampati classification predicts intubation difficulty based on the visibility of intraoral structures. Classes III and IV predict difficult intubation. B, A short thyromental distance (less than 6 cm or 3 fingerbreadths) when the head is extended predicts difficult intubation.

Figure 4.4, Cormack and Lehane grading of laryngeal views during laryngoscopy. A, Grade I. Most of the glottis is visible. B, Grade II. The posterior aspect of the glottis is visible. C, Grade III. Only the epiglottis is seen; no part of the laryngeal inlet is visible. D, Grade IV. The epiglottis is not visible. Patients with grades I and II are usually easy to intubate with direct laryngoscopy, whereas those with grades III and IV are often difficult; the ability to see the arytenoid cartilage is the important difference.

Many of these predictors cannot be assessed in the emergency setting. Some of the key predictors are apparent simply by observing the external appearance of the patient's head and neck. Patients with neck tumors, thermal or chemical burns, traumatic injuries involving the face and anterior aspect of the neck, angioedema, infection of pharyngeal and laryngeal soft tissues, or previous operations in or around the airway suggest a difficult intubation because distorted anatomy or secretions may compromise visualization of the vocal cords. Facial or skull fractures may further limit airway options by precluding nasotracheal (NT) intubation. Patients with ankylosing arthritis or developmental abnormalities such as a hypoplastic mandible or the large tongue of Down's syndrome are difficult to intubate because neck rigidity and problems of tongue displacement can obscure visualization of the glottis.

Besides these obvious congenital and pathologic conditions, the presence of a short, thick neck is one of the more common predictors of a difficult airway. Such individuals are easily identifiable by observing the head and neck in profile. Obesity alone may not be an independent predictor of difficult intubation, but obese patients with large-circumference necks are likely to be difficult to intubate. Facial hair can complicate a difficult airway by rendering BMV ineffective because of the lack of a good mask seal. One patient type that does not immediately stand out as a difficult intubation, but can be surprisingly so, is a patient with an unusually long mandibulohyoid distance (the thyroid prominence appearing low in the neck) and a short mandibular ramus. Visualization of the larynx is difficult because of the distance to the larynx and the relative hypopharyngeal location of the tongue.

Knowledge of the poor performance of difficult airway predictors should not make emergency providers more cavalier about using RSI; rather, it should create more concern. The solution is not to avoid RSI because lack of paralysis makes every intubation more difficult. Even though predicting a difficult airway is challenging, and even though a comprehensive airway assessment may not be possible because of patient behavior or clinical circumstances, performing an assessment of the airway is important and serves as a cognitive forcing strategy that guides the physician to plan and prepare for the airway intervention. It is essential to appreciate the critical importance of having a clear backup plan when intubation with RSI fails. This situation mandates the need for a preconceived algorithm that uses proven rescue techniques applicable to a broad range of clinical scenarios, such as the bougie (flexible intubating stylet) and the intubating LMA Fastrach (Teleflex). The value of the bougie is indisputable, and it is clear that using the intubating LMA Fastrach after failed RSI has decreased the frequency of failed airways and the need for surgical intervention. Because RSI is the “go-to” method for emergency intubation, providers must be prepared to perform a surgical airway when laryngoscopy, BMV, and backup devices fail.

Review Box 4.1, Direct laryngoscopy: indications, contraindications, complications, and equipment.

Emergency Airway Decision Making

The airway provider must have many tools readily available to deal with an acutely compromised airway. It is important to be proficient in a number of different techniques and to tailor their use to the needs of the individual patient. Rescuers should practice potential scenarios before facing patients with a compromised airway. Failure to do so may lead to unnecessarily aggressive management in some situations or to irreversible hypoxic injury as a result of hesitation in others. Deciding who requires a definitive airway and who needs only supportive measures is a formidable task for even the most skilled clinician.

The following parameters should be assessed before the decision is made to establish a definitive airway:

Adequacy of current ventilation
Potential for hypoxia
Airway patency
Need for neuromuscular blockade (uncooperative, full stomach, teeth clenching)
Cervical spine stability
Safety of the technique and skill of the operator

Consideration of these factors should guide the clinician in deciding if tracheal intubation is necessary, and in selecting the optimal technique. Choosing the initial approach is often straightforward. Difficulty arises precipitously when the initial approach fails. Time becomes critical as the risk for irreversible hypoxic injury and cardiac arrest rises. Anxiety then increases the potential for error. Forethought and practice are invaluable when managing these situations.

Clinicians who perform emergency intubation, especially RSI, must understand that oxygenation and ventilation, not tracheal intubation, are paramount when caring for critically ill patients. Patients who are hypoxic on arrival and those who develop hypoxia after a failed first intubation attempt need good BMV to restore oxygenation and keep them stable enough for further intubation attempts. The importance of BMV skills cannot be overstated (see Chapter 3 ), and mastery of this skill alleviates much of the anxiety associated with difficult emergency airways and improves the chance for successful RSI. It is critically important to have an extraglottic airway (EGA) device immediately available during every RSI in the event that BMV is difficult or impossible. All clinicians who perform emergency intubation should be prepared to perform a surgical airway when intubation methods and backup ventilation techniques fail.

Decision to Perform Rapid-Sequence Intubation (RSI)

RSI in anesthesia has evolved since the introduction of succinylcholine in 1951. RSI was initially used as an abbreviation for rapid-sequence induction but is now synonymous with rapid-sequence intubation. Initially, the main purpose of RSI was to decrease the risk for aspiration in patients with full stomachs who needed emergency intubation. RSI has now become the most common method of emergency airway management because paralysis facilitates optimal intubating conditions in critically ill patients.

Emergency providers should be very careful to not use RSI in a cavalier manner. When giving a paralytic agent, the provider takes complete responsibility for airway maintenance, ventilation, and oxygenation of the patient. Consider one of many awake intubation (i.e., intubation without paralysis) options in patients with known or anticipated difficult airways ( Box 4.2 ). In the emergency setting it is useful to think of difficult airways as situations in which our usual methods of intubation and backup ventilation/oxygenation techniques fail. The goal should be to avoid RSI in patients who cannot be easily intubated via the common techniques (direct or video laryngoscopy) and cannot be ventilated with a bag-mask device. Risk factors for difficult or impossible BMV have been well studied and include the presence of a beard, obesity, lack of teeth, age older than 55 years, a history of snoring, short thyromental distance, and limited mandibular protrusion (see Box 3.2 in Chapter 3 ). It is also prudent to consider whether an EGA device will be difficult to place because this is often the primary backup plan. RSI is contraindicated in patients who cannot be orally intubated and it should usually be avoided in patients with laryngotracheal abnormalities caused by tumors, infection, edema, or a history of cervical radiation therapy.

Box 4.2

Intubation Methods for Emergency Airway Management

Direct laryngoscopy
Video laryngoscopy
Video/Optical laryngoscope with a tube channel
Flexible Endoscope
Intubating laryngeal mask airway
Optical stylet
Blind nasal
Retrograde

If the clinician decides that RSI is not appropriate for a patient, there are many options that can be performed without paralysis (see Box 4.2 ). Flexible endoscopic intubation is the go-to procedure for most anesthesiologists and is described later in the chapter. Direct and video laryngoscopy can also be performed without paralysis. If excellent topical anesthesia is achieved, some patients can be intubated without any sedation.

Ideal Versus Emergency Technique

The intubation plan that would be best in the ideal/elective situation is often not the best plan in the emergency setting. Consider the patient with rapidly increasing upper airway swelling due to angioedema or anaphylaxis, causing impending complete airway obstruction. Because of predicted difficulty with direct and video laryngoscopy, some providers would not consider this patient a candidate for RSI. Other intubation strategies might have a higher chance of success if time was not a factor. The patient will likely develop complete airway obstruction, critical hypoxia, and death in the time required to set up and perform endoscopic nasal intubation. In this situation the emergency provider is “forced to act” to complete timely tracheal intubation. The best course for this patient is likely RSI with modern video laryngoscopy equipment and a good backup plan, such as the LMA Fastrach (Teleflex), followed by a cricothyrotomy. There are many other scenarios in which the emergency airway plan is much different than the ideal/elective airway plan, such as patients with severe trauma who have multiple different life-threats. In these patients, intubation often needs to be expedited so that other life threats can be addressed in a timely manner.

Failed Airways

A failed airway should be differentiated from a known or anticipated difficult airway. A patient is considered to have a failed airway in the following situations : (1) inability to maintain oxygenation by BMV or EGA device; (2) failure of three or more intubation attempts by an experienced operator; (3) failure of the first attempt in a “forced to act” situation.

If a patient has a failed airway, and oxygenation can be maintained, the clinician should attempt intubation by another method (e.g., flexible endoscopy, intubating LMA [ILMA], video laryngoscopy, surgical airway, and others); if a more experienced provider is not already present then one should be called for. This could be an anesthesiologist, emergency physician, paramedic, or any other clinician with significant airway expertise. If at any point there is failure of oxygenation, an EGA device should be placed while preparing for a cricothyrotomy. If the EGA device cannot oxygenate, a cricothyrotomy should be performed.

Emergency Airway Algorithm

The realization that one cannot predict all cases of failed BMV and failed laryngoscopy mandates the need for a simple preconceived algorithm that uses proven rescue techniques that are applicable to a broad range of clinical scenarios, such as the bougie and the LMA Fastrach (Teleflex). The value of the bougie is indisputable, and it is clear that use of the LMA Fastrach after failed RSI has decreased the frequency of failed airways and the need for surgical airways.

One of the most important concepts to appreciate when using RSI is that of optimal laryngoscopy to maximize first-pass success. Preparation, preoxygenation, proper patient positioning, anterior neck maneuvers, and good laryngoscopy skills are all important components of optimal laryngoscopy. Just as important as optimal laryngoscopy is the ability to recognize when laryngoscopy (or any technique) has failed and when it is time to move on to a different approach. Patient safety during RSI depends on the provider's ability to maintain ventilation and oxygenation if the first attempt at intubation fails. Critical decisions about how to maintain ventilation and oxygenation and when to use a different intubation approach are much easier when using a simple preconceived algorithm. The algorithm presented here summarizes the general approach used in the Department of Emergency Medicine at Hennepin County Medical Center ( Fig. 4.5 ). This algorithm is presented as an example. Individual providers and institutions should determine their own algorithms based on the availability of skills and resources. There are many similarities between this algorithm and those put forth by the American Society of Anesthesiologists and the Difficult Airway Society; however, our algorithm is simpler and more applicable to emergency airway management. Most published airway algorithms are not ideal for emergency airway management because they do not account for the conditions that are commonly encountered: patients with full stomachs who are critically ill and often uncooperative, and intubations that cannot be canceled if the airway is too difficult. Many algorithms resemble wish lists of equipment and skills that are simply not available to many emergency airway providers. Our algorithm is based on the concept that oxygenation, not intubation, is the key. It stresses well-proven concepts, procedures, and devices, and it is modeled after a simple algorithm developed by Combes and colleagues that was validated in a large prospective study.

Figure 4.5, Emergency airway management algorithm used at Hennepin County Medical Center. The end point of the algorithm is successful tracheal intubation. This algorithm is presented as an example. Individuals and institutions should formulate their own algorithms based on technical skills and the availability of resources. ILMA, Intubating laryngeal mask airway.

Direct Laryngoscopy (DL)

Despite the proliferation of approaches and devices designed to secure a definitive airway, DL remains the mainstay of tracheal intubation. DL is a crucial skill even in the era of video laryngoscopy, and is less prone to problems such as device failure or blood and secretions covering the video lens. Visual confirmation of the tube going through the vocal cords is usually possible.

Indications and Contraindications

DL is indicated in any clinical situation in which a definitive emergency airway is necessary, including routine and difficult airways. Relative contraindications to DL include limited mouth opening, upper airway distortion or swelling, severe kyphosis, or copious blood or secretions.

Equipment

Laryngoscope

There are two basic blade designs for DL, curved (Macintosh) and straight (Miller) ( Fig. 4.6 ). Each comes in various adult and pediatric blade sizes. Slight variations in laryngoscopic technique follow from the choice of blade design, and it is often a matter of personal preference. The tip of the straight blade goes under the epiglottis and lifts it directly, whereas the curved blade fits into the vallecula and indirectly lifts the epiglottis via engagement of the hyoepiglottic ligament to expose the larynx.

Each blade type has advantages and disadvantages. The straight blade is often a better choice in pediatric patients, in patients with an anterior larynx or a long floppy epiglottis, and in individuals whose larynx is fixed by scar tissue. It is less effective, however, in patients with prominent upper teeth, and it is more likely to damage dentition. Use of the straight blade is also more often associated with laryngospasm because it stimulates the superior laryngeal nerve, which innervates the undersurface of the epiglottis. A straight blade may inadvertently be advanced into the esophagus and initially reveal unfamiliar anatomy until it is withdrawn. The blade has a lightbulb at the tip, which may slightly hamper vision. The wider, curved blades are helpful in keeping the tongue retracted from the field of vision and allowing more room for passing the tube through the oropharynx, and they are generally preferred for uncomplicated adult intubations. Aside from patient considerations, some clinicians prefer the curved blade because they find that it requires less forearm strength than the straight blade.

The illumination provided by the laryngoscope can make a big difference in the ability to visualize the laryngeal inlet. The importance of these factors is underappreciated, as demonstrated by Levitan in a survey of the Macintosh blades used in 17 Philadelphia EDs. It was found that only 24% of all blades provided the brightness necessary for fine inspection. This finding was largely explained by the fact that the majority of EDs used the A-Mac (American) as opposed to the clearly superior brightness design of the G-Mac (German) or the intermediate brightness of the E-Mac (English).

Tracheal Tubes

The standard adult endotracheal (ET) tube measures approximately 30 cm in length. Tube size is typically printed prominently on the tube and is based on the internal diameter (ID) and measured in millimeters. The range is 2.0 to 10.0 mm in increments of 0.5 mm. The outer tube diameter is 2 to 4 mm larger than the ID. Tubes are also imprinted with a scale in centimeters that indicates the distance from a tube's distal tip.

Adult men can generally accept a 7.5- to 9.0-mm orotracheal tube, and women can usually be intubated with a 7.0- to 8.0-mm tube. Larger tubes are theoretically desirable because airway resistance increases as tube size decreases, but in practice, a 7.5-mm tube is adequate for almost all patients. In emergency intubations, particularly if a difficult intubation is anticipated, many clinicians choose a smaller tube and change to a larger tube later if necessary. Though generally an acceptable practice, this should be avoided in burn patients because swelling may prohibit subsequent tube placement. For nasal intubation, a slightly smaller (by 0.5 to 1.0 mm) tube may be easier to advance through the nasal passages.

Correct tube size is important in the pediatric population. It is especially important when using an uncuffed tube because a good seal is needed between the ET tube and the upper part of the trachea ( Table 4.1 ). As tube size is based on the ID, a cuffed tube should generally be a half size (0.5 mm) smaller than an uncuffed tube. The smaller ID of an appropriately sized, small cuffed tube could theoretically make it more prone to plugging from secretions. Cuffed tubes are available down as small as 3 mm ID, although indications for these tubes in neonates and infants are rare. A cuffed tube is used in children with decreased lung compliance who may require prolonged mechanical ventilation. In a child, the smallest airway diameter is at the cricoid ring rather than at the vocal cords, as in adults. Hence, a tube may pass the cords but go no farther. If this should occur, the next smaller size tube should be passed. The American Heart Association (AHA) states that both cuffed and uncuffed tubes are acceptable for infants and children who are tracheally intubated. If a cuffed tube is placed, careful attention must be paid to cuff pressures.

TABLE 4.1

Tracheal Tube Sizes for Average Patients

AGE	CUFFED ETT SIZE (INTERNAL DIAMETER, mm)	EQUIVALENT TRACHEOTOMY TUBE SIZE
Children
Preterm	2.5	00
Term	3.0	00
6 months	3.0–3.5	00–0
1–2 years	4.0	0–1
3–4 years	4.5	1–2
5–6 years	5.0	2
10 years	6.0	3
12 years	7.0	4
14 years	See adult sizing
Adults
Female	7.0–8.0	5
Male	7.5–9.0	6

In children 2 years or older, the following formula is a highly accurate method for determining correct uncuffed and cuffed ET tube size:

Uncuffed tube size (mm) = [Age (yr) / 4] + 4

$Uncuffed tube size (mm) = [Age (yr) / 4] + 4$

Cuffed tube size (mm) = [Age (yr) / 4] + 3

$Cuffed tube size (mm) = [Age (yr) / 4] + 3$

For most clinical situations, using the width of the nail of the patient's little (fifth) finger as a guide is sufficiently accurate and has been shown to be more precise than finger diameter ( Fig. 4.7 ). In order to reduce cognitive load during emergency situations, it may be best to use a length-based tool to determine the appropriate size ET tube, tube depth, and other resuscitation measures.

Figure 4.7, Pediatric endotracheal (ET) tube size estimation using the fingernail width of the patient's little finger. In children, a cuffed or uncuffed ET tube may be used.

A standard tracheal tube uses a high-volume, low-pressure cuff to avoid pressure necrosis of the tracheal lining. A clinical test for determining correct cuff inflation is to slowly inject air until no air leak is audible while the patient is receiving bag-tube ventilation. This usually occurs with 5 to 8 mL of air if the proper size tracheal tube has been selected. Many clinicians use the tension of the pilot balloon as a guide to cuff inflation. Slight compressibility with gentle external pressure indicates adequate inflation for most clinical situations. For long-term use, measure and maintain cuff pressure at 20 to 25 mm Hg. Capillary blood flow is compromised in the tracheal mucosa when cuff pressure exceeds 30 mm Hg. In emergency situations, simply inflate the balloon with 10 mL of air and adjust it when the patient's condition has stabilized.

Interest in design of the tip of the tracheal tube has grown as the Seldinger technique is increasingly being applied to intubation. When a tracheal tube is passed over a smaller-caliber introducer (Seldinger technique), regardless of whether it is a tracheal tube introducer or an endoscope, there is a reasonable chance that the tube will get hung up on the laryngeal soft tissue. A tracheal tube that has been designed to overcome this problem has a bevel oriented posteriorly and a flexible tip that decreases the distance between the tube and whatever it is being passed over ( Fig. 4.8 ).

Figure 4.8, Comparison of the standard tracheal tube tip with the Parker Flex-Tip Tracheal Tube (Parker Medical, Engelwood, CO). Note : When a standard tube is inserted in the normal fashion, the bevel is oriented vertically and toward the patient's left. The Parker tube tip bevel faces posteriorly and may avoid getting caught on laryngeal structures. The flexible tip of the Parker tube also provides a closer fit on an introducer.

Check the ET tube cuff for leaks by inflating the pilot balloon before attempting intubation. Prepare the tube for placement by passing a malleable stylet down the tube to increase its stiffness and enhance control of the tip of the tube. Do not extend the stylet beyond the eyelet of the tube. Bend the tube and stylet to create a “straight-to-cuff” shape with a 35-degree distal bend. Lubricate the tip and cuff of the tube with viscous lidocaine or a water-soluble gel.

Optimal Patient Positioning for DL

The sniffing position, with the patient's head extended on the neck and the neck flexed relative to the torso, has traditionally been considered the best head position for DL. This position aligns the oral, pharyngeal, and laryngeal axes ( Fig. 4.9 A – C ). Horton and colleagues described the ideal sniffing position for normal patients as neck flexion of 35 degrees and atlanto-occipital extension such that the plane of the face is −15 degrees to the horizontal position. In supine patients, neck flexion is achieved by head elevation. Depending on the size and shape of the patient, the amount of head elevation may differ significantly, and the end point should be horizontal alignment of the external auditory meatus with the sternum. In normal-size adults it is usually possible to achieve the sniffing position with 7 to 10 cm of head elevation. Morbidly obese patients require much more head elevation to achieve the proper sniffing position. In these patients, aligning the external auditory meatus with the sternum requires elevation of the head and neck, as well as the upper part of the back (see Fig. 4.9 D ). This can be accomplished by building a ramp of towels and pillows under the upper torso, head, and neck or by using a Troop Elevation Pillow (Mercury Medical, Clearwater, FL) or similar device. Alternatively, elevating the head to a 25-degree back-up position (keeping the patient supine while placing the bed in 25-degree reverse Trendelenburg) may achieve the same purpose.

Figure 4.9, Head positioning for tracheal intubation. A, Neutral position. B, Head elevated. C, “Sniffing” position with a flexed neck and extended head. Note that flexing the neck while extending the head lines up the various axes and allows direct laryngoscopy. D, Morbidly obese patients are best intubated in a ramped position with elevation of the upper part of the back, neck, and head; the ideal position aligns the external auditory canal and the sternum.

Two studies have shown that elevating the head (flexing the neck) beyond the sniffing position often improves visualization of the glottis. Because the amount of head elevation needed for optimal laryngoscopy varies depending on individual patient anatomy, it is important to make laryngoscopy a dynamic procedure. This is best accomplished by putting your right hand behind the patient's head to lift, flex, and extend the head as needed to bring the glottis into view. Optimal positioning of the head and neck is not possible in trauma patients who require in-line stabilization of the cervical spine. This is one of the aspects that makes trauma airways so challenging and makes other maneuvers, such as external laryngeal manipulation (ELM), even more important in these patients. It should also be noted that some patients, especially those who are obese, are in neck extension when lying supine because of upper dorsal fat deposition. If this is noted, the head can be raised until the head and neck are in neutral position.

Procedure and Technique of DL

Learning DL

Existing data suggests that novices who learn tracheal intubation skills with video laryngoscopy have higher success rates at DL compared to novices who learn tracheal intubation skills with DL. When utilizing DL alone, it is estimated that at least 50 intubations need to be performed to achieve greater than 90% success. Using a video laryngoscopy system that allows both direct and video laryngoscopy (video systems with a Macintosh blade) may be ideal for learning DL skills.

Adults

Place the patient in the supine position with the head at the level of the lower part of the intubator's sternum ( Fig. 4.10 , step 2 ). To maintain the best mechanical advantage, keep your back straight and do not hunch over the patient. Bend only at the knees ( Fig. 4.11 ). Keep the left elbow relatively close to the body and flex it slightly to provide better support. In a severely dyspneic patient who cannot tolerate lying down, perform DL with the patient seated semi-erect and the clinician on a stepstool behind the patient.

Figure 4.11, Proper positioning of the clinician, patient, and assistant for tracheal intubation. The following points are demonstrated: the difficult airway cart is adjacent to the patient, the suction device is at the head of the bed, the patient is in the “sniffing position” with the occiput elevated and the clinician's right hand ready for additional adjustment if necessary, the bed is elevated and the clinician is at the appropriate distance from the patient, and the laryngoscope handle is angled at 45 degrees.

Grasp the laryngoscope in the left hand with the back end of the blade pressed into the hypothenar aspect of your hand. Draw the patient's lower lip down with your right thumb, and introduce the tip of the laryngoscope into the right side of the patient's mouth (see Fig. 4.10 , step 3 ). Slide the blade along the right side of the tongue while gradually displacing the tongue toward the left as you move the blade to the center of the mouth (see Fig. 4.10 , step 4 ). If you initially place the blade in the middle of the tongue, it will fold over the lateral edge of the blade and obscure visualization of the airway. Placing the blade in the middle of the tongue and failing to move the tongue to the left are two common errors that prevent visualization of the vocal cords ( Fig. 4.12 ).

Figure 4.12, Common problems encountered when using a laryngoscope. A, The laryngoscope blade is under the middle of the tongue, with the sides of the tongue hanging down and obscuring the glottis. B, The tongue is not pushed far enough to the left and is obscuring the glottis. C, Correct blade position with the tongue elevated and to the left. D, Use of the curved (Macintosh) laryngoscope blade. E, Use of the straight (Miller) blade.

As you move the tip of the blade toward the base of the tongue, exert force along the axis of the laryngoscope handle by lifting upward and forward at a 45-degree angle (see Fig. 4.10 , step 6 ). The direction of this force is critical because if the force is too horizontal or too vertical, poor visualization will result. Avoid bending the wrist because it can result in dental injury if the teeth are used as a fulcrum for the blade. Slowly advance the blade down the tongue, searching for the epiglottis. It may help to have an assistant retract the cheek laterally to further expose the laryngeal structures. Locating the epiglottis is a crucial step in laryngoscopy, and has been termed epiglottoscopy . The laryngeal inlet lies just distal and below the epiglottis.

The step after visualization of the epiglottis depends on which laryngoscope blade is being used. With the curved blade, place the tip into the vallecula, the space between the base of the tongue and the epiglottis (see Fig. 4.12 D ). Continued anterior elevation of the base of the tongue will partially lift the epiglottis. With the blade in the midline of the vallecula, engage the hyoepiglottic ligament with the tip of the blade to indirectly lift the epiglottis and expose the laryngeal inlet. If the tip of the blade is inserted too deeply into the vallecula, the epiglottis may be pushed down and obscure the glottis. When using the straight blade, insert the tip under and slightly beyond the epiglottis and directly lift it up (see Fig. 4.12 E ). If the straight blade is placed too deeply, the entire larynx may be elevated anteriorly and out of the field of vision. Gradually withdraw the blade to allow the laryngeal inlet to drop down into view. If the blade is deep and posterior, the lack of recognizable structures indicates esophageal passage; gradually withdraw the blade to permit the laryngeal inlet to come into view.

Infants and Children

It is helpful to appreciate the anatomic differences between children and adults when intubating pediatric patients ( Fig. 4.13 and Table 4.2 ). Children's proportionately larger heads naturally place them in the sniffing position, so a towel under the occiput is rarely necessary ( Fig. 4.14 ). The large head of newborns can result in a posterior positioning of the larynx that prevents visualization of the vocal cords. A small towel under the infant's shoulders should correct this problem. This is not necessary in all children; rather, the goal of any positioning maneuvers should be alignment of the tragus with the anterior shoulder.

Figure 4.13, Sagittal section of the neck of an infant. Note that in small children, the neck is shorter and the larynx is located more cephalad.

TABLE 4.2

Comparison of the Airway in Adults and Children

COMPARISON	CHILD	ADULT	CLINICAL CONSEQUENCES OR ADJUSTMENTS FOR CHILDREN
Head	Proportionately larger (up to approximately age 10 yr)	Proportionately smaller	A child is naturally in the sniffing position when supine. Do not place a towel under the occiput; a child may benefit from elevation of the shoulders. The large head may be “floppy” and require the assistant to hold the head still during intubation.
Teeth	Easily knocked out	Stable unless decay or trauma is a factor	Teeth may be knocked out and aspirated or forced into trachea.
Tonsils or adenoids	Large and friable	Generally not a problem	Nasotracheal intubation in a child may cause excessive bleeding and is not recommended. Adenoid or tonsil tissue may plug the endotracheal tube or cause airway obstruction from aspiration.
Tongue	Relatively larger	Relatively smaller	The tongue is difficult to displace anteriorly in a child. Consider using a straight blade.
Larynx	Opposite C2-C3	Opposite C4-C6	A more superiorly located larynx or an “anterior” larynx is more difficult to visualize. Consider using a straight blade.
Epiglottis	U shaped, shorter, stiffer	Flatter, more flexible	The epiglottis is more difficult to manipulate in a child; it may fold down and obstruct the view with use of a curved blade. Consider using a straight blade.
Vocal cords	Concave upward; anterior attachment of the cords lower than posterior, thereby creating a slant	Horizontal	A concave shape does not affect intubation, but it may affect ventilation. For partial airway obstruction or to break laryngospasm, consider positive pressure ventilation with a jaw-lift maneuver to open the arytenoids. The anterior superior slant of the vocal cords may cause the endotracheal tube to hang up on the anterior commissure as it passes into the larynx. Rotate the tube 90 degrees counterclockwise. Overextension of the neck may cause partial airway obstruction as a result of airway collapse.
Length of the trachea	Relatively shorter	Relatively longer	A short trachea increases the likelihood of main stem bronchus intubation. Follow the formula for correct depth of placement (cm depth = 0.5 × age [yr] + 12) measured from the corner of the mouth. The double black line on the endotracheal tube should pass just beyond the cords.
Airway diameter	Relatively smaller; smallest diameter at the cricoid ring	Relatively larger; smallest diameter between the vocal cords	Laryngoscope-induced trauma, edema, and foreign material will significantly alter the diameter of the airway. Be gentle. Extremes of flexion or extension may kink the airway. If trouble with bag-valve-mask ventilation occurs, reassess the degree of head flexion or extension. Cricoid pressure may cause complete airway obstruction. The endotracheal tube may pass through the cords but be too large to pass through the cricoid ring. If unable to pass into the trachea, use the next smaller tube.
Residual lung capacity	Relatively smaller	Relatively larger	A child becomes hypoxic more quickly than an adult does. Closely monitor O ₂ saturation and avoid prolonged periods without ventilation.

Figure 4.14, Oral intubation in a child with a straight blade. The proportionately large floppy head of a child may present some difficulty, and an assistant may be required to hold the child's head straight.

The head may also be floppy and may benefit from stabilization by an assistant. The child's increased tongue-to-oropharynx ratio and shorter neck hinder forward displacement of the tongue and, when coupled with a U-shaped epiglottis, can make visualization of the glottis difficult. DL in infants and young children is generally best performed with a straight blade: Miller size 0 for premature infants, size 1 for normal-sized infants, and size 2 for older children. The infant's larynx lies higher and relatively more anterior. If no laryngeal structures are visible after laryngeal pressure, gradually withdraw the blade. Inadvertent advancement of the blade into the esophagus is a common error.

Cricoid Pressure, ELM, Bimanual Laryngoscopy, and BURP

The differences between cricoid pressure, ELM, and backward, upward, rightward pressure (BURP) are often misunderstood. Cricoid pressure is the application of pressure at the anterior cricoid ring to displace it posteriorly to attempt to occlude the esophagus, with the intent of preventing regurgitation and aspiration; cricoid pressure is not intended to improve visualization during laryngoscopy. ELM is the application of pressure on the thyroid cartilage during laryngoscopy to help optimize visualization of the glottis. BURP is often the best combination of forces that need to be applied to the thyroid cartilage during ELM. Bimanual laryngoscopy refers to use of the right hand to perform ELM.

Cricoid Pressure

There is some good evidence that cricoid pressure (Sellick's maneuver) helps prevent gastric inflation during BMV, though cricoid pressure during BMV reduces tidal volume, increases peak inspiratory pressure, and prevents good air exchange.

The only evidence suggesting that cricoid pressure prevents regurgitation during intubation consists of five cadaver studies, one human study, and some case reports, which is poor evidence by today's standards of evidence-based medical practice. There are mixed data about the effects of cricoid pressure and laryngoscopic view, and several studies have shown that it worsens visualization of the larynx. A Cochrane review found insufficient evidence to support or refute the use of cricoid pressure during intubation. There are many reports of significant regurgitation and aspiration regardless of the application of cricoid pressure. Cricoid pressure also decreases successful insertion of and intubation through LMAs. Despite the lack of evidence, many experts believe that Sellick's maneuver is critical during RSI.

Because aspiration has dire consequences and because cricoid pressure has traditionally been considered integral to patient safety during emergency airway management, it is reasonable to apply cricoid pressure as long as it does not interfere with ventilation and intubation. There is significant evidence that it can interfere with ventilation and intubation, so it is best to apply cricoid pressure on a case-by-case basis with a full understanding of the benefits and drawbacks of cricoid pressure. If cricoid pressure is utilized, it should be released immediately if there is any difficulty either intubating or ventilating a patient in an emergency setting. Routine use of cricoid pressure during BMV of patients in cardiac arrest is not currently recommended in the AHA Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. It is reasonable to release or relax cricoid pressure during insertion of an LMA, during intubation with an ILMA, or if ventilation with the LMA is difficult.

Some authors believe that improper technique is to blame for the many reported failures of Sellick's maneuver. The proper technique for applying Sellick's maneuver is to place the thumb and middle finger on either side of the cricoid cartilage and the index finger in the center anteriorly. Apply 30 N (6.7 lb.) of force to the cricoid cartilage in the posterior direction. As a reference, approximately 40 N of digital force on the bridge of the nose will usually cause pain.

ELM, Bimanual Laryngoscopy, and BURP

ELM is the application of pressure on the thyroid cartilage in an attempt to improve the view of the larynx during laryngoscopy. Multiple studies have shown that ELM performed by the laryngoscopist (bimanual laryngoscopy) is superior to having an assistant apply anterior neck pressure. Bimanual laryngoscopy is best because the direction and amount of force that will optimize laryngeal exposure is variable. BURP is sometimes optimal, and it often worsens the laryngoscopic view, so it is best to move the larynx in a variety of directions to determine the optimal ELM. The best way to quickly apply a variety of different forces to the larynx to determine the optimal ELM is by manipulation of the larynx with the laryngoscopist's right hand ( Fig. 4.15 ).

Figure 4.15, External laryngeal manipulation (ELM) (or bimanual laryngoscopy). A, ELM step 1. The laryngoscopist optimizes view of the larynx by reaching around to the patient's neck with the right hand and manipulating the thyroid cartilage while performing laryngoscopy. B, ELM step 2. The assistant's hand replaces the laryngoscopist's hand on the anterior aspect of the neck and maintains the position of the larynx while the laryngoscopist places the tracheal tube.

Operator-directed posterior displacement of the larynx during laryngoscopy was described by Brunnings in 1912. After Sellick described the use of cricoid pressure to avoid regurgitation in 1961, it became common to have an assistant apply anterior neck pressure during laryngoscopy. In 1993, Knill reported that having an assistant apply BURP to the cricoid or thyroid cartilage improved visualization of the glottis during two cases of difficult laryngoscopy. In 1993, Takahata and coworkers performed a prospective study of 630 intubations and found that BURP produced better laryngeal exposure than just backward pressure in patients with difficult laryngoscopy. A 2005 prospective crossover trial by Snider and colleagues found no benefit with routine application of the BURP maneuver.

Studies by Benumof, Levitan, and colleagues have demonstrated that it is best to apply pressure on the thyroid cartilage (not the cricoid cartilage) and suggested that ELM should be applied by the laryngoscopist's right hand, not by an assistant. They also found that the direction of force required for optimal ELM was not always upward and rightward and that the amount of backward pressure was variable. In a 1996 study of 181 patients, Benumof and Cooper found that external manipulation was optimal when applied to the thyroid cartilage in 88% of patients and to the cricoid cartilage in only 11% of patients. In a 2006 cadaveric study of 1530 laryngoscopies by 104 laryngoscopists, Levitan and associates found that bimanual laryngoscopy was more effective than both BURP and cricoid pressure for optimizing laryngeal exposure ( Figs. 4.16 and 4.17 ; see also Fig. 4.15 ). In addition, they found that cricoid pressure worsened the view of the larynx in 29% of cases and BURP worsened it in 35%. In a 2002 study of eight first-year emergency medicine residents performing 271 intubations in an operating room setting, Levitan and colleagues found that bimanual laryngoscopy (ELM performed by the laryngoscopist) consistently improved laryngeal exposure by novice intubators.

Figure 4.16, The epiglottis is elevated and visualization of the vocal cords is improved by applying pressure on the hyoepiglottic ligament and external laryngeal manipulation.

Figure 4.17, Note the assistant manipulating the anterior part of the neck and retracting the cheek for better visualization.

Bimanual laryngoscopy with ELM should be performed whenever the laryngeal view is not optimal after good laryngoscopic technique. To perform this procedure, the intubator applies posterior pressure on the thyroid cartilage. The force vector (right or left, upwards or downwards, and amount of posterior pressure) will vary patient to patient, and the intubator should find the force vector that provides the best laryngeal view. Once this is established, an assistant applies the same force vector to the thyroid cartilage as the intubator removes pressure to free the hand in order to pass the tracheal tube. The assistant holds pressure while the intubator completes tracheal intubation.

Passing the Tube

Once the vocal cords have been visualized, the final step is to pass the tube through the vocal cords and into the trachea under direct vision. It is best to use a malleable stylet for all emergency intubations. The best stylet shape is straight with a 35-degree hockey-stick bend at the proximal cuff (“straight-to-cuff”). In a 2006 study, Levitan and colleagues showed that stylet bend angles greater than 35 degrees made ET tube passage more difficult.

Hold the tube in your right hand and introduce it from the right side of the patient's mouth. Lateral retraction of the cheek by an assistant may greatly aid overall visualization (see Fig. 4.17 ). Advance the tube toward the patient's larynx below the line of sight with the bend facing upward. When advanced in this manner, the tube does not obstruct the view of the larynx until the last possible moment before the tube enters the larynx. If the patient is not chemically paralyzed, pass the tube during inspiration, when the vocal cords are maximally open. It enters the trachea when the cuff disappears through the vocal cords. Advance the tube 3 to 4 cm beyond this point. It is not enough to see the tube approach the cords; watch the tube pass through the vocal cords to ensure tracheal placement. Directly observing the tube pass through the cords is the best way to immediately confirm correct placement. If part of the glottis is visualized and it is difficult to pass the tube, consider using a bougie (tracheal tube introducer).

Tracheal Tube Introducer (Bougie)

If DL does not bring the vocal cords fully into view, a tracheal tube introducer may be used to facilitate intubation. This adjunct is a long, thin, semirigid introducer that, with the aid of a laryngoscope, is passed through the laryngeal inlet and over which an ET tube is advanced through the cords and into the trachea. The technique, originally described more than 60 years ago by Macintosh, was recommended for patients in whom visualizing the vocal cords was difficult. It has also been shown to be effective when the laryngeal inlet cannot be visualized at all. It is the most common airway adjunct used in British EDs for complicated intubations. Its efficacy has been demonstrated prospectively during difficult intubations in the operating room, as a pivotal component of a difficult airway algorithm in the operating room, and when compared with conventional laryngoscopy in the ED.

A variety of tracheal tube introducers are available today ( Fig. 4.18 ). The original adjunct was called the gum elastic bougie, or simply “the bougie,” and is currently available in a reusable form for both adult and pediatric patients (Eschmann Tracheal Tube Introducer, Portex Sims, Kent, UK). The adult size comes in two forms: a 60-cm (15-Fr) version with a short, 40-degree hockey-stick curve at the end, and a straight one that is 70 cm. The adult version can accommodate a 5.5-mm ET tube. The pediatric version is 70 cm (10-Fr) and straight and can accommodate a 4.0-mm tube. A polyethylene introducer designed for single use is also available and comes only in the 60-cm version (Flextrach ET Tube Guide, Greenfield Medical Sourcing, Austin, TX). A variation of this concept is the FROVA Introducer (Cook Critical Care, Bloomington, IN), a plastic introducer with a similar profile to the others except that it has a hollow lumen through which the patient can be ventilated when an accompanying adapter is attached.

Figure 4.18, Several types of tracheal tube introducers. The classic introducer, the gum elastic bougie, A , is reusable and comes in curved- and straight-tipped adult forms and a straight pediatric form. The straight bougies, B, are 70 cm long and the curved-tipped bougies are 60 cm long. The blue introducer, C, (Flextrach ETTube Guide, Greenfield Med., Austin, TX) is polyethylene and designed for single use and comes only in a curved-tipped adult form (60 cm). D, Create a 60-degree bend in the distal portion of the introducer if the laryngeal inlet cannot be seen on laryngoscopy.

Consider using a tracheal tube introducer when a difficult airway is anticipated; it can also be helpful in all intubations when visualization of the laryngeal inlet is limited. A trauma patient with cervical spine precautions is a typical example. The presence of blood and vomitus rarely prevents placement of the bougie into the trachea. Its safety record is impressive despite decades of use, and reports of complications are rare.

Shaping the introducer may not be necessary in many cases, but with difficult laryngeal views, create a 60-degree bend in the distal introducer (see Fig. 4.18 D ). Ideally, tracheal tube introducer-assisted intubation is a two-person procedure ( Fig. 4.19 ). As laryngoscopy begins, the assistant has both a styletted ET tube and bougie prepared and available. The intubator performs laryngoscopy in the normal fashion to obtain the best possible view of the larynx. If the cords are in full view, proceed with intubation using a styletted ET tube. If the view is suboptimal, an assistant can pass the tracheal tube introducer to the operator for placement anterior to the arytenoids and into the larynx. If only the epiglottis is visible, place the introducer, with a 60-degree distal bend, just under the epiglottis and direct it anteriorly. With the laryngoscope still in place and the introducer stabilized by the operator, the assistant slides the ET tube over the introducer. Pass the tube through the larynx. Just before entering the larynx, rotate the tube 90 degrees counterclockwise to avoid having the tip of the ET tube get caught on the laryngeal structures ( Fig. 4.20 ). Withdraw the laryngoscope and confirm proper tube placement. While securing the ET tube, ask the assistant to remove the introducer.

Figure 4.19, Two-person tracheal tube introducer technique. The introducer is handed to the clinician after the best glottic view has been obtained. A, The clinician places the introducer (the black line positioned at the teeth indicates the proper introducer depth to ensure stable positioning within the trachea while providing enough length to grasp the end of the introducer before passing the tube). B, An assistant passes the tracheal tube over the introducer as the clinician holds the introducer steady. C, The clinician passes the tracheal tube with a 90-degree counterclockwise rotation as the tube approaches the glottis, and the assistant withdraws the introducer.

Figure 4.20, A common cause of difficulty when railroading an endotracheal (ET) tube over a tracheal tube introducer. A, The tip of the ET tube is caught on the right arytenoid as it is being railroaded over the introducer. B, Corrective maneuvers: (1) withdrawal of the ET tube 2 cm to disengage the arytenoids and (2) counterclockwise 90-degree rotation of the ET tube to orient the bevel posteriorly. C, The bevel of the ET tube is facing posteriorly and allows smooth passage through the glottis.

There are a number of findings that confirm successful introducer placement. If any portion of the arytenoids is visible and the introducer was seen to pass anterior to them without resistance, the introducer is in the airway. Unlike seeing an ET tube “go through the cords” when in fact the laryngeal inlet may have been momentarily obscured by the tube or balloon, the smaller-caliber introducer does not obscure the view of the glottis and thus avoids this potential pitfall. In addition to better visual confirmation, successful passage is indicated, up to 90% of the time, by feeling clicks produced by the angled tip of the introducer as it strikes against the tracheal rings. An assistant will also usually feel confirmatory movement in the airway if the anterior aspect of the neck is palpated. If there is still any question whether the introducer is in the airway, gently advance it at least 40 cm, at which point resistance should be felt as the introducer passes the carina and stops inside a main bronchus. If the bougie does not stop when advanced approximately 40 cm, the introducer is most likely in the esophagus. Withdraw it and reattempt placement.

Several technical points should be emphasized. The first is that it is important to create a curve in the distal portion of the introducer when the laryngeal inlet is not visible. This is not uniformly appreciated, even in England where the bougie is used commonly. It is a mistake to think that the factory-formed curve at the tip will be sufficient to access the glottis in these situations. Second, in some cases the bougie will pass through the cords but will become lodged in the anterior trachea and not be able to be advanced further. If this happens, withdraw slightly and rotate the bougie 90 degrees clockwise to move the curved tip to the patient's right. This will prevent the tip from striking the anterior trachea and allow the bougie to pass to the carina. Third, if there is difficulty passing an ET tube into the laryngeal inlet, this is most likely because the tip of the tube is caught on the right arytenoid cartilage. In this case, withdraw the tube 2 cm, rotate it 90 degrees counterclockwise, and advance it again (see Fig. 4.20 ). Fourth, although there may be some benefit to lubricating the distal end of the introducer, in emergency intubations, lubricating the full length of the introducer makes it slippery and hard to handle without conferring any obvious advantage. Lubricating the ET tube, conversely, remains critical for smooth passage through the vocal cords. Fifth, a common error when first using the tracheal tube introducer is to remove the laryngoscope before passing the ET tube over the introducer. This often results in difficulty placing the tube because it is displaced posteriorly by the weight of the pharyngeal soft tissues and gets hung up on the laryngeal structures. Reinsert the laryngoscope. Pull the tube back 2 cm to disengage the soft tissue. Rotate the tube 90 degrees counterclockwise and then readvance it. Sixth, in instances in which it is difficult to get the introducer sufficiently anterior to access the laryngeal inlet, make sure that the introducer lines up with the operator's line of vision. If the introducer enters the mouth at a significant angle above this line, most often when the clinician is too close to the patient, it may be deflected posteriorly by the lip or intraoral structures and escape the attention of the operator. This creates the impression that the introducer is “too floppy.”

In the prehospital setting, where assistance might not be available, the laryngoscope should be removed to mount the ET tube onto the introducer. Once the tube is on the introducer, reinsert the laryngoscope and advance the introducer through the glottic opening. Advance the ET tube while rotating it 90 degrees counterclockwise to ensure successful passage into the trachea. Mounting the tube onto the introducer to insert them as a unit is not advised because it is often difficult to direct the introducer into the laryngeal inlet as it moves within the ET tube.

Laryngospasm

If the patient is not paralyzed, laryngospasm, or persistent contraction of the adductor muscles of the vocal cords, may prevent passage of the tube. Pretreatment with topical lidocaine may decrease the likelihood of laryngospasm, though this is not routinely performed. After laryngospasm is noted, one option is to spray lidocaine (2% or 4%) directly onto the vocal cords. An infrequent but effective means of achieving tracheal anesthesia is transtracheal puncture and injection of 3 to 4 mL of lidocaine through the cricothyroid membrane. Laryngospasm is usually brief and often followed by a gasp. Be ready to pass the tube at this moment. Occasionally, the spasm is prolonged and needs to be disrupted with sustained anterior traction applied at the angles of the mandible, as in the jaw-thrust maneuver. Do not force the tube at any time because it could cause permanent damage to the vocal cords. Consider using a smaller tube. Prolonged, intense spasm may ultimately require muscle relaxation with a paralyzing drug (see Chapter 5 ). Pediatric patients are far more prone to laryngospasm than adults. In a child, if vocal cord spasm prevents passage of the tube, a chest-thrust maneuver may momentarily open the passage and permit intubation.

Positioning and Securing the Tube

Secure the ET tube in a position that minimizes both the chance of inadvertent, main stem endobronchial intubation and the risk for extubation. The tip should lie in the midtrachea with room to accommodate neck movement. Because tube movement with both neck flexion and extension averages 2 cm, the desired range of tip location is between 3 and 7 cm above the carina.

The average tracheal length is between 10 and 13 cm. On a radiograph, the tip of the tube should ideally be 5 ± 2 cm above the carina when the head and neck are in a neutral position. On a portable radiograph, the adult carina overlies the fifth, sixth, or seventh thoracic vertebral body. If the carina is not visible, it can be assumed that the tip of the tube is properly positioned if it is aligned with the third or fourth thoracic vertebra. In children, the carina is more cephalad than in adults, and it is consistently situated between T3 and T5. In children, T1 is the reference point for the tip of the ET tube.

Estimate the proper depth of tube placement before radiographic confirmation by using the following formulas, in which length represents the distance from the tip of the tube to the upper incisors in children and from the upper incisors or the corner of the mouth in adults:

Children: Tracheal tube depth (cm) = [age (yr) / 2] + 12
(or use length-based aid such as a Broselow tape)

Adults: Women: Tracheal tube depth (cm) = 21 cm

Med: Tracheal tube depth (cm) = 23 cm

In adults, this method has been shown to be more reliable than auscultation in determining the correct depth of placement. One can anticipate that tall male patients will often require deeper placement, to 24 or 25 cm, and that short women will often require a shallower placement of 19 or 20 cm.

Inflate the cuff to the point of minimal air leak with positive pressure ventilation. In an emergency intubation, inflate with 10 mL of air and adjust the inflation volume after the patient is stabilized.

After placement of the tracheal tube, auscultate both lungs under positive pressure ventilation. Take care to auscultate posterolaterally because auscultation anteriorly can reveal sounds that mimic breath sounds and arise from the stomach. With the tube in position and the cuff inflated, secure the tube in place. Attach commercial ET tube holders, adhesive tape, or umbilical (nonadhesive cloth) tape securely to the tube and around the patient's head ( Figs. 4.21 and 4.22 ). Position the tube at the corner of the mouth, where the tongue is less likely to expel it. This position is also more comfortable for the patient and allows suctioning. A bite block or oral airway to prevent crimping of the ET tube or damage from biting is commonly incorporated into the system used to secure the tube.

Figure 4.21, Technique for taping an endotracheal tube. The method illustrated can be replaced by using a commercial holder or tracheostomy cloth tie. Avoid taping the lips.

Figure 4.22, A, A commercial disposable tube holder is ideal and preferred to secure an endotracheal (ET) tube without the use of messy tape. B, A plastic disposable ET holder firmly secures the ET tube with a small clamp. C, When positioning a patient for transfer to another bed or for a chest radiograph, ensure the integrity of the ET tube by placing the right hand firmly against the right side of the face while holding the tube securely with the same hand. The other hand immobilizes the neck.

Unintentional extubation can have disastrous consequences, particularly if the patient was difficult to intubate initially. Secure the ET tube immediately after correct placement has been confirmed. Orotracheal intubation is associated with a higher rate of unplanned extubation than NT intubation. During transport, moving the intubated patient, or obtaining radiographs, designate one person to tend to the ET tube to avoid unplanned extubation. Inadequate sedation is another risk factor for unplanned extubation. If long-acting paralytics have not been administered, consider sedation or physical restraints to prevent self-extubation by an agitated or confused patient.

Confirmation of Tracheal Tube Placement

Clinical Assessment

Confirm tracheal placement clinically by seeing the tube pass through the vocal cords ( Table 4.3 ). If any question remains, apply posterior pressure on the ET tube while the laryngoscope is still in place and expose the tube by altering the angle as it passes between the cords. Absent or diminished breath sounds, any sound or vocalization, increased abdominal size, and gurgling sounds during ventilation are clinical signs of esophageal placement. If the patient can moan or groan, the tube is not in the trachea! Critically, esophageal placement is not always obvious. One may hear “normal” breath sounds if only the midline of the thorax is auscultated. The presence of condensation of the ET tube as a means of confirming tracheal placement may also be misleading. Blinded observers noted condensation of the ET tube during ventilation in 23 of 27 esophageal intubations in an animal model. One way to clinically assess tracheal placement after several ventilations or during spontaneous respiration is to note whether air is felt or heard to exit through the tube after cuff inflation. If tidal volume is adequate, the exit of air should be obvious.

TABLE 4.3

Assessing Proper Tube Placement

TEST	INTERPRETATION
Observe the tube pass through the vocal cords	Accurate way to ensure placement; if in doubt, look again after intubation
End-tidal CO ₂ measurements	Reliable if a good persistent waveform is present; can be misleading with nasotracheal intubation if the tip is curled supraglottically: it will give a positive CO ₂ reading
Auscultation of breath sounds over the chest	May be misleading, especially if only the midline is examined; listen in both axillae
Auscultation over the stomach	Gurgling indicates esophageal placement
Condensation (fog) forms inside the tube with each breath	Not reliable to confirm tracheal placement
Observe the chest rise with positive pressure and fall with release	Generally reliable if good chest rise is present; may be absent in patients with a small tidal volume or severe bronchospasm
Feel air exiting from the end of the tube after inflation	Reliable
Air remains in the lung after the end of the tube is occluded and exits when the occlusion is removed	Reliable, but one may “ventilate” a closed area of the esophagus
Ask the patient to speak; listen for moaning or other sounds	If the tube is in proper place, no sound is possible
Chest radiograph	Cannot always differentiate between tracheal and esophageal placement. If known to be in the trachea by other measures, radiography can assess for proper depth of tube insertion.
Aspiration technique	Tracheal location is confirmed (assuming patient ET tube) if 30–40 mL of air is aspirated without resistance; probable esophageal location if unable to aspirate the syringe easily or delayed bulb refill occurs; can be misleading with nasotracheal intubation if the tube has curled supraglottically
Fiberoptic bronchoscope	Reliable if tracheal rings are seen down the endotracheal tube
Lighted stylet down the endotracheal tube	Reliable if transillumination seen in the low midline portion of the neck
Ultrasound detection of tracheal tube location	Appears to be reliable but not extensively studied

Asymmetric breath sounds indicate probable main stem bronchus intubation. Because of the angles of takeoff of the main bronchi and the fact that the carina lies to the left of midline in adults, right main stem intubation is most common and is indicated by decreased breath sounds on the left side. When asymmetric sounds are heard, deflate the cuff and withdraw the tube until equal breath sounds are present. Bloch and coworkers reported accurate pediatric tracheal positioning if after noting asymmetric breath sounds the tube is withdrawn a defined distance beyond the point at which equal breath sounds are first heard: 2 cm in children younger than 5 years and 3 cm in older children.

Esophageal Detector Device

An aspiration technique used to determine ET tube location was first described by Wee in 1988. The technique takes advantage of the difference in tracheal and esophageal resistance to collapse during aspiration to locate the tip of the tracheal tube. After intubation, attach a large syringe (Positube esophageal detector, Flotec, Indianapolis, IN) to the end of the ET tube and withdraw the plunger of the syringe. If the tube is placed in the trachea correctly, the plunger will pull back without resistance as air is aspirated from the lungs. If the tracheal tube is in the esophagus, resistance is felt when the plunger is withdrawn because the pliable walls of the esophagus collapse under the negative pressure and occlude the end of the tube. Another device that uses the same principle as syringe aspiration is the self-inflating bulb (e.g., Ellick device).

In the initial study conducted in an operating room, tube placement was identified correctly in 99 of 100 cases (51 esophageal, 48 tracheal). The result was considered equivocal in the remaining case. That tube was removed and found to be nearly totally occluded with purulent secretions. Slight resistance was noted in one patient with right main stem intubation; the resistance decreased when the tube was pulled back. Before use, always check the esophageal detector device for air leaks. If any connections are loose, the leak may allow the syringe to be withdrawn easily, thereby mimicking tracheal location of the tube.

When using the aspiration technique, apply constant, slow aspiration to avoid occlusion of the tube from tracheal mucosa drawn up under the high negative pressure. If the tracheal tube is placed correctly, 30 to 40 mL of air can be aspirated without resistance. If air was initially aspirated and some resistance is then encountered, the tracheal tube should be pulled back between 0.5 and 1.0 cm and rotated 45 degrees. This takes the tube out of the bronchus if it has been placed too deeply and changes the orientation of the bevel if the tube has been temporarily occluded with tracheal mucosa. Air is easily aspirated if the tube was in the trachea, but repositioning it will make no difference if the tube was in the esophagus. The syringe aspiration technique can be used before or after ventilation of the patient. Inflation of the tube cuff has no effect on the reliability of the test. This device is reliable, rapid, inexpensive, and easy to use.

A squeeze-bulb aspirator is an alternative to the syringe technique. Attach the bulb to the ET tube and squeeze; if the tube is in the esophagus, it is accompanied by a flatus-like sound followed by absent or markedly delayed refilling. Insufflation of a tube in the trachea is silent with instantaneous refill. An early study with the Ellick evacuator bulb device reported that 82% of esophageal intubations were identified. A later study using a slightly different bulb device (Respironics, Murrysville, PA) found that all 45 esophageal intubations were detected. The device is cheap, easy to use, and operated single-handedly in less than 5 seconds. The bulb should not be used in freezing temperatures because of loss of elasticity. Confusion may occur if the esophageal tube is tested more than once because subsequent inflations may be silent. With repeated assessments, false-positive refilling of the bulb may occur as a result of instillation of air during the first attempt. This observation has led to a recommendation that the bulb be compressed before it is attached to the ET tube. Delayed, though complete refilling of the bulb may occur with bronchial tube placement or placement in the more pliable pediatric airway. The bulb suction modification of the aspiration technique has not been studied as thoroughly as the syringe technique.

A significant number of false positives occur with esophageal detection devices (the tube is correctly placed in the trachea, but the device suggests that it is in the esophagus). These patients are almost uniformly obese. Endoscopic evaluation found that the tracheal wall was invaginated into the ET tube because of the negative pressure. In such circumstances, if the intubation was felt to be successful, visually re-confirm that the ET tube is through the cords before removing the ET tube. Alternatively, if the patient has a perfusing rhythm and an expired CO ₂ device is available, it should be used. To date, there has been one reported case of unrecognized esophageal intubation undetected by the syringe aspiration technique. In this case there was marked gastric distention from forceful BMV. The esophageal detection device is not reliable in confirming tracheal tube depth and position after intubation because easy aspiration of air will occur if the tip of the tube is located supraglottically (expired CO ₂ will also be misleading).

End-Tidal CO ₂

End-Tidal CO ₂ detection is probably the best technique, apart from visualizing the tube pass through the cords, to confirm tracheal placement of the ET tube. A high level of CO ₂ in exhaled air is the physiologic basis for capnography and the principle on which end-tidal CO ₂ pressure (P etco ₂ ) detectors were developed (see Chapter 2 ). Continuous waveform capnography is recommended by the AHA guidelines as the most reliable method of confirming and monitoring correct placement of an ET tube (class I, level of evidence [LOE]). This recommendation is based on multiple studies showing 100% accuracy of waveform capnography for detecting correct ET tube placement. Continuous waveform capnography is accurate even in cardiac arrest. Patients with prolonged cardiac arrest will still have a typical square waveform but a low P etco ₂ value.

When waveform capnography is not available, emergency providers may have to rely on colorimetric CO ₂ indicators, which correspond to CO ₂ levels flowing through the device when placed on the tracheal tube adapter (see Fig. 4.10 , step 10 ). The typical device displays opposite colors (e.g., yellow and purple) to indicate low levels of CO ₂ in esophageal gas versus the high levels of CO ₂ exhaled from the respiratory tree. Handheld quantitative or semiquantitative electronic CO ₂ monitors are also available. Eventually, all prehospital defibrillators will have advanced monitoring capability that includes capnography.

A multicenter study of a colorimetric device demonstrated an overall sensitivity of 80% and a specificity of 96%. In patients with spontaneous circulation and an inflated tracheal tube cuff, the sensitivity and specificity were 100%. The poor sensitivity (69%) noted in patients in cardiac arrest was due to the fact that low exhaled CO ₂ levels were seen with both very-low-flow states and esophageal intubation. The device must be used with caution in cardiac arrest victims. CO ₂ levels return to normal after return of spontaneous circulation. Colorimetric changes may be difficult to discern in situations with reduced lighting, and secretions can interfere with the change in color. Regardless of the monitoring device, patients should be ventilated for a minimum of six breaths before taking a reading. Recent ingestion of carbonated beverages can result in spuriously high CO ₂ levels with esophageal intubation. Colorimetric changes do not exclude supraglottic positioning of the tip of the ET tube. Adequate ventilation and oxygenation may be achieved in the supraglottic position, but there is still a risk for aspiration in the absence of a protected airway and the potential for further tube dislodgment. Glottic positioning may be difficult to detect clinically. The only signs may be persistent cuff leak or diminished chest rise with ventilation. Radiographic evidence or direct visualization confirms the diagnosis.

Ultrasound Detection of Tracheal Tube Location

Some data suggest that transtracheal ultrasound may play a future role in confirming tracheal location of the ET tube location after intubation. All studies are small, and sensitivity ranges from 96% to 100% for confirming tracheal placement, whereas specificity (detecting esophageal intubation) ranges from 88% to 100%. If the ET tube is the in the trachea, acoustic shadowing is seen posterior to the anterior tracheal rings only. If the ET is in the esophagus, the esophagus is opened by the ET tube and shadowing is seen posterior to the anterior esophageal wall (as well as the trachea). This method relies on the esophagus being located in the paratracheal position; if the esophagus is directly posterior to the trachea, then detecting esophageal intubation is very difficult.

Sonographic sliding signs can also be used immediately after tracheal intubation is confirmed by waveform capnography to evaluate for main stem intubation prior to obtaining a chest radiograph. Assuming there is no other underlying lung pathology, absence of sliding on the left after intubation indicates probable right main stem intubation. The ET tube can be withdrawn 2 cm, and sliding signs reassessed.

Comparison of Detector Devices

In the setting of spontaneous circulation, both syringe aspiration and P etco ₂ detection are highly reliable means of excluding esophageal intubation. An animal study comparing these techniques with clinical assessment and measuring the speed and accuracy of determining tube placement demonstrated that both the syringe esophageal detector device and P etco ₂ detection were highly accurate, approaching 100%. The esophageal detector device was more rapid, with determination in 13.8 seconds versus 31.5 seconds for P etco ₂ detection. The detector device remained accurate when air was insufflated into the esophagus for 1 minute, thus simulating unrecognized esophageal placement. Clinical assessment alone yielded an alarming 30% rate of failure to identify esophageal intubation. In the setting of cardiac arrest, the aspiration method is more reliable than colorimetric CO ₂ detection, although waveform capnography remains reliable even in low flow states.

An unequivocal method for determining tracheal tube location uses the endoscope. Passage of the scope through the tube with visualization of the tracheal rings confirms ET placement and position within the trachea. Placement of a lighted stylet down the tracheal tube and successful transtracheal illumination can also be used to determine correct ET placement.

At present, there is no perfect device for confirmation of ET tube placement in all situations. Be aware of the limitations of each device; it is ideal to use multiple means of confirmation to ensure tracheal placement of the ET tube.

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