Normal and difficult airway management

History

The crux of any clinical assessment is a thorough history and physical. Ascertaining the history for and identifying on exam the characteristics that are predictive of a difficult airway or postprocedure respiratory concerns allow clinicians to tailor an appropriate perianesthetic plan to better manage such factors ( Table 19.1 ). Although the ideal is to identify all potential difficult airways preoperatively, this may not be practical given that current assessment techniques are not highly sensitive or specific ( ). Therefore the clinician must assume that any patient could become a difficult or failed airway.

The review of the airway history includes a child’s typical breathing pattern, looking for signs and symptoms of obstruction. This assessment should include how the child sleeps, noting the significance of snoring, preferred position(s), and any associated apnea. A child who does not snore will rarely have an innate anatomic reason for airway obstruction during induction and mask ventilation.

Congenital and acquired abnormalities of the head and neck often are associated with difficult airway management (see Table 19.2 ). A review of other family members with syndromes should be ascertained, because many syndromes are associated with variable penetrance and varying phenotypic expression. The Committee on Nomenclature and Classification of Craniofacial Anomalies of the American Cleft Palate-Craniofacial Association has organized anomalies into five categories: clefts, synostosis, hypoplasia, hyperplasia, and unclassified. Each category has associated disorders with difficult airway management.

Reviewing the airway management on any prior anesthetic records is essential, as this provides insight into past successes, failures, and any potential concerns. This includes obtaining records from other institutions and is particularly valuable in anticipated difficult airway cases. The review should seek any changes that may have occurred in a child’s airway anatomy compared with prior anesthetic records. A review of photographs of the child over the course of time can also aid in predicting potential airway difficulties.

Physical examination

Though factors predictive of difficult airways are not very sensitive or specific, there are a number of physical characteristics that have been associated with difficult airways. These factors include age less than 1 year, ASA Status III and IV, Mallampati scores of III and IV, low BMI, obesity, neck restriction (C-spine instability, halo application, C-collar), small mandibular space, large tongue, craniofacial abnormalities, short lower lip–to-chin distance, retrognathia, cleft palate, short tragus-to-mouth distance, genetic syndromes, and congenital heart disease.

Diagnostic studies

Diagnostic studies to evaluate a child’s airway may be helpful in determining or clarifying anatomic and physiologic concerns. This may present a conundrum in that anesthesia is often needed to perform the child’s imaging study. If imaging studies are needed, plain films of the head, neck, and chest may provide information on the location and any underlying pathology that may compromise the respiratory system (i.e., parenchymal disease, upper and lower airway distortions). These films may also reveal locations of obstructions, narrowing, masses, or foreign bodies. Cooperative children may tolerate more detailed airway studies such as CT and MRI scans. These scans can be rendered into digital 3-D modeling of the airway or even a printed 3-D model for more realistic assessment of potential approaches. However, younger and uncooperative children may require an anesthetic to accomplish these studies. If there is a concern for difficulty with mask ventilation or intubation, or if it is unclear whether a supraglottic airway device (SAD) is feasible, then a multidisciplinary discussion is required to determine the risks and benefits of such diagnostic exams requiring anesthesia. If the decision is to proceed with imaging and anesthesia, then the management of the difficult airway patient may be approached by securing the airway in the main operating suite and then transferring the anesthetized patient to the imaging location for the study. The challenges faced during induction and maintenance of anesthesia will then determine where best to emerge the patient: imaging location or operating room.

Another tool to help evaluate a patient’s airway is flexible fiberscopic endoscopy. Endoscopic evaluation with a flexible fiberscope via the nasal passages is an assessment tool commonly performed by pediatric otolaryngology in clinic and throughout the hospital. These exams are performed almost always with only local anesthesia, reassurance, and (depending on patient cooperation) various levels of restraint by the guardian or other individuals. Flexible fiberscopy is a worthwhile skill for a pediatric anesthesiologist and will complement their skill set with flexible fiberscopic intubations. Regardless of one’s skill set, it is always prudent to consult a pediatric otolaryngologist to help assess challenging airways and to provide any necessary backup.

Any child with a difficult airway in respiratory distress should have appropriately trained personnel immediately available to manage the airway in an operating room setting. Once the airway is secured, further diagnostic testing can be performed.

Preoperative optimization

Children often have comorbidities which may require preoperative consultation by another specialty to optimize the patient’s underlying medical condition prior to a scheduled procedure. Optimizing the child’s medical status with coexisting morbidities, such as complex congenital heart disease or pulmonary disease, can decrease the perioperative anesthetic risk. Such consults to other services are for optimizing the patient’s underlying medical issues and not for providing clearance for the procedure. The decision to proceed is still the purview of the anesthesiologist.

Decision tree for the airway management plan

Anesthetic preparations must include a decision tree for the airway management that determines:

• 1.

  Whether sedation or anesthesia will be needed

• 2.

  The number of attempts at securing the airway with the initial technique

• 3.

  Who performs the first and any subsequent attempt(s) at securing the airway

• 4.

  Contingency plans regarding alternate techniques and providers

The anesthetic management plan, choice of airway equipment and technique depends on the individual practitioner’s preferences, skill set, available institutional resources, and the surgical requirements. The most important determination is to decide whether to secure the airway with the child awake, sedated, or under general anesthesia, and this decision will be based on whether the provider can ventilate the patient with a mask or a SAD. reported the incidence of difficult mask ventilation in children 0 to 8 years of age as 6.6% but only a 1.2% incidence of difficult intubation. When a plan has been developed, a preoperative discussion with the family and a review with the surgical service(s) are essential. The family needs to be informed of the added issues and risks associated with their child’s conditions, including the potential need for an emergent surgical airway and possible intensive care unit admission and postprocedure ventilation. There should also be a surgeon available who can perform a surgical airway in all known difficult airway cases.

Retrospective studies using patient registries have reported that the first attempt at intubation is generally the best attempt at securing the airway. Thus optimizing patient position, equipment, and even personnel should be performed prior to and not after the first attempt. Multiple airway management studies have revealed that first attempts at intubation may fail in up to 20% of patients without a difficult airway and in 70% with a difficult intubation ( ; ; ; ; ). These studies also show a corresponding exponential increase in associated complications with additional attempts (see Fig. 19.1 ). Risk factors for patient complications included:

• 1.

  >2 tracheal intubation attempts

• 2.

  weight <10 kg

• 3.

  micrognathia

• 4.

  three direct laryngoscopy attempts before switching to an indirect method

Finally, an extubation plan should also be determined and given equal weight to the intubation plan (see Restoration of the Natural Airway). Therefore a preinduction decision tree for the airway management of each case is essential, with the hope that a smooth and predecided plan will improve overall success, patient safety, and patient outcomes.

Airway equipment

Once an anesthetic plan is determined, the necessary airway equipment is prepared and appropriate personnel notified. As airway experts, individual anesthesiologists need to be well versed in multiple techniques and approaches. Table 19.3 divides approaches into five categories represented by the columns ranging from traditional approaches for the categories within the first row, such as direct laryngoscopy, to more advanced techniques on the lower rows, involving video laryngoscopy, flexible fiberscopic intubation, SAD, combined techniques, and invasive or surgical interventions. Anesthesiologists should become proficient with as many techniques and uses of equipment as possible. The subglottic approaches require more advanced expertise and are generally performed by surgeons.

TABLE 19.3

Airway Techniques for Intubation

Direct View	Indirect View	Supraglottic and Periglottic	“Blind”	Subglottic or Front of Neck Access
Direct laryngoscopy or video-assisted direct laryngoscopy *	Rigid videolaryngoscopy † with standard blades (Miller or Macintosh)	Facemasks, oral/nasal airways Supraglottic airway devices
Parson’s blade Anterior commissure blade	Rigid videolaryngoscopy with nonstandard (“hyperangulated”) and channeled blades	Intubating ‡ and second-generation § supraglottic airway devices	Tracheal tube guides (gum elastic bougie)	Retrograde
Specialty blades	Flexible fiberscope (flexible bronchoscopy)	Multitude of other devices	Lightwands	Transtracheal jet ventilation
	Rigid and semirigid Video/optical stylets		Digital ||	Cricothyrotomy Tracheostomy
Combined or Hybrid Techniques
Flexible videolaryngoscopy via supraglottic airways Flexible videolaryngoscopy combined with retrograde Rigid videolaryngoscopy combined with rigid and semirigid video stylets Flexible videolaryngoscopy combined with rigid laryngoscopy (direct or indirect views)

* Video-assisted direct laryngoscopy is a technique where the laryngoscope blade mimics the shape of a traditional direct laryngoscopy blade and can therefore be used to perform standard direct laryngoscopy while another provider observes the intubation via the screen. Please refer to the Video-Assisted Direct Laryngoscopy section.

† Videolaryngoscopy has become accepted nomenclature for rigid videolaryngoscopy. “Rigid” is added in here for emphasis and distinction.

‡ Intubating supraglottic airway devices adds the ability to pass the pilot balloon through the device for pediatric sizes for more effective and efficient intubation through such devices.

§ Second-generation devices are those that allow gastric decompression via an esophagogastric port.

|| Digital refers to a clinician using fingers to feel the laryngeal structures and guide the tracheal tube through it.

Oftentimes the most versatile and effective methods of securing complex and difficult airways are through combining equipment and techniques from various categories; for example, intubating with a flexible fiberscope via a SAD with continuous ventilation (spontaneous, assisted, or controlled) ( ) or using a two-person technique of video laryngoscopy and flexible fiberscopic guidance of the tracheal tube.

The key point regarding airway techniques is that each technique should be used regularly: first to acquire and then to maintain proficiency. To achieve this experience with less invasive techniques, a combination of mannequins and patients with normal airways can be used. The invasive techniques can be practiced on manikins or animal models and cadavers.

Natural airway

Sedation or general anesthesia for minimally invasive procedures (e.g., radiologic studies, lumbar punctures, endoscopies) can often be performed in a patient spontaneously breathing without any airway adjuncts except supplemental oxygen. To maintain spontaneous respiration, it is essential to have proper positioning of the patient and optimal airway patency. Anesthesia involving a natural airway uses noninhalation techniques such as total continuous intravenous anesthesia, intermittent IV dosing, intramuscular dosing, alimentary canal dosing (oral, nasal, or rectal), or a combination of these. A subset of patients may require airway support with oral or nasal airways. If appropriate, any noninvasive airway support (continuous positive airway pressure [CPAP], bilevel positive airway pressure [BiPAP], humidified high-flow nasal oxygen) that the patient is already using should be continued. A natural airway can also be used during shared airway surgery, where surgical access may be impeded by the presence of a tracheal tube or SAD (see Shared Airway).

Face mask ventilation

The ability to provide positive pressure ventilation and oxygenate a patient with a face mask remains an essential core skill for an anesthesia provider. Difficulties with face mask ventilation are estimated to occur in approximately 1.4% of adult patients ( ) and in approximately 6% of children ( ). In infants and children with anatomic abnormalities that are associated with difficult airways, the incidence may be higher. In the Pediatric Difficult Intubation Registry (PeDI-R), reported that children who were difficult to intubate had a 17% incidence of difficult mask ventilation.

Avoiding insufflation of the stomach by maximizing airway patency is vital when face mask ventilation is used. Neonates and infants are even more prone to gastric insufflation and its detrimental consequences compared with older children. With increasing abdominal distension, respiration is further compromised as tidal volumes and functional residual capacity are decreased (see Chapter 3 : Respiratory Physiology). Gastric air insufflation during positive-pressure face mask ventilation consistently occurs at 16 to 20 cm H ₂ O peak inspiratory pressure ( ). As an anesthesiologist attempts to counteract the airway obstruction, higher inspiratory inflating pressures are used and more gas is forced into the stomach. This further interferes with and compromises the patient’s respiratory status. As soon as face mask ventilation is commenced, indicators of adequate ventilation must be verified. These indicators include good chest wall excursion with minimal abdominal expansion, normal pulse oximetry readings, and a reliable capnograph tracing. If these signs are absent, then efforts are directed at improving the patient’s airway patency by initially performing a jaw-thrust maneuver. This maneuver lifts the base of the tongue up and away from the glottis. It is also important to ensure the mouth is not fully closed when masking. This helps to avoid obstruction of the oral cavity by the anesthesia provider’s fingers compressing the submandibular soft tissues that can press the tongue onto the palate ( Fig. 19.2 A–B). By lifting the mandible and avoiding submandibular compression, the tongue will not adhere to the palate nor drop into the posterior pharynx. This will allow air to pass more easily via both the nasal and oral passages ( Fig. 19.3 A–C). Mastering this technique will also allow users to decrease the need for oral airways during a mask induction.

However, even with optimal mask skills there still may be a need for the appropriate use of airway adjuncts, such as oral or nasopharyngeal airways. These adjuncts can increase airway patency, provide adequate ventilation at lower airway pressures, and minimize gastric insufflation. Finally, switching from a single-handed mask-holding technique to a two-handed technique may also improve the ability to mask ventilate while minimizing gastric insufflation ( ). A sole provider can perform two-handed masking by employing pressure ventilation modes (pressure support or pressure control) while awaiting additional help. Pressure modes are preferred, as the peak inspiratory pressure can be more readily limited than volume modes.

Supraglottic airway devices

The original SAD, the laryngeal mask airway, was described by . Its introduction in the practice of anesthesia markedly changed the approach to airway management. SADs are designed to surround the glottis, occlude the esophagus, and—with an adequate seal around the larynx—enable positive pressure ventilation and oxygenation while minimizing gastric insufflation (see Fig. 17.22 in Chapter 17 : Equipment). The initial descriptions of SADs in children included their use in difficult airway management during infant cleft palate repair ( ), radiation therapy ( ), and otologic surgery ( ). The first formal assessment of SADs in children was published by .

SADs have gradually evolved in their design. The first-generation devices were designed so that the tip would sit inside the esophagus to sufficiently occlude it and decrease the risk of gastric distension and aspiration (see Figs. 17.19 and 17.21 in Chapter 17 : Equipment). The second-generation devices now include a gastric access channel allowing a gastric tube to be placed or simple venting to occur. The second-generation devices also have improved cuff designs that typically allow higher ventilation pressures to be used. These modifications aim to further decrease the risk of gastric distension and aspiration ( ; ).

There is insufficient evidence as to which manufacturer’s SAD performs the most effectively in children, and there is a paucity of evidence for their use in neonates and infants. The largest evidence-based source of information covers first-generation devices. performed a meta-analysis to compare the clinical properties of various SADs used in children. The clinical end points included device failure rates, oropharyngeal leak pressure, and blood staining. Mihara and colleagues concluded that the LMA ProSeal may be the best SAD for children because of its high oropharyngeal leak pressure and low failure rate (see Table 19.4 ); nevertheless, providers must consider other device qualities when choosing a SAD.

For example, if intubating through a SAD with a cuffed endotracheal tube (ETT), not all SADs are designed to facilitate intubation with a cuffed ETT and pilot balloon (see Fig. 17.20 A–B in Chapter 17 : Equipment). Though pilot balloons can be removed and reassembled when removing the SAD over the tracheal tube, one needs to be familiar with the steps to replace the pilot balloon before the combined technique is performed ( ). An airway exchange catheter can be passed through the airway conduit of the LMA Supreme, whereas an ETT cannot.

In addition to being an airway adjunct for the routine administration of an anesthetic, SADs are also an important component of the algorithm in managing the difficult or failed pediatric or adult airway. A SAD can act as a conduit for intubation while allowing continuous ventilation and oxygenation. SADs provide a temporizing ability to ventilate and oxygenate a patient before intubation with an advanced airway technique; if intubation is no longer considered feasible, a SAD can act as an airway rescue device for the patient who was difficult to ventilate/oxygenate. This last scenario allows an option to complete the procedure or emerge the patient from anesthesia. A SAD can also provide an airway to ventilate and/or oxygenate a patient during a crisis and may be more effective than mask ventilation, particularly in a setting where mask ventilation is difficult and gastric distension is a problem. In these latter situations, a second-generation device may also allow decompression of the distended stomach without the need to interrupt ventilation and oxygenation.

Tracheal intubation

Tracheal intubation remains the mainstay of pediatric airway management. The placement of a tracheal tube through the vocal cords provides airway security in a fashion the other techniques do not.

Tracheal tubes

There are many different types of tracheal tubes available for use in children (see Chapter 17 : Equipment). Tracheal tubes are usually made from polyvinyl chloride (PVC) and can be cuffed with a balloon at the distal end of the tube, which can be inflated to create a seal within the airway. Tracheal tubes can also be uncuffed with no distal balloon; as such, the seal (or lack thereof) is dependent on the size of the external diameter of the tracheal tube relative to the internal diameter of the trachea (or bronchus). The sizing of all tracheal tubes is based on the internal diameter (ID) of the tube (e.g., a 3.0 tracheal tube has a 3-mm internal diameter). The external or outer diameter (OD) of the tracheal tube determines which size is appropriate for any individual patient. Internal diameters of tracheal tubes are consistent, whereas the external diameter differs between manufacturers, and the presence of a distal cuff adds approximately 0.5 mm to this outer diameter (see Table 32.1 in Chapter 32 : Anesthesia for Thoracic Surgery). There are also significant differences among manufacturers with respect to cuff size, shape (spherical versus cylindrical), length, location on the tube, and volume/pressure characteristics (see Fig. 17.13 A–B in Chapter 17 : Equipment). Historically, concerns about damage to narrow areas of the pediatric (particularly the infant or neonatal) airway led to recommendations that uncuffed tracheal tubes should be used in children. However, the use of cuffed tracheal tubes over the past 2 decades has increased due to improved cuff design that has limited the transmural pressure on the tracheal wall. In addition, the ability to monitor cuff pressure with simple manometry has also influenced the acceptance of cuffed tubes in clinical practice. The growing use of cuffed tracheal tubes has not been associated with a notable increase in airway-related complications. In a Cochrane review, noted that the use of cuffed tubes was associated with fewer tube changes, less anesthetic gas use, and no increase in postextubation stridor.

Tracheal tubes also have different designs that are related to their clinical use. The tubes include the following:

• 1.

  Preformed, angled oral or nasal Ring-Adair-Elwyn (RAE) tubes designed for dental and oromaxillofacial procedures.

• 2.

  Parker tubes that have a proboscis-like structure at the tip of the tube, designed to bend over the opening of the tracheal tube to limit possible trauma and “hangups” or entrapment and to allow the tube to better “glide” past anatomic structures on advancement into the larynx, particularly when sliding over tracheal tube guides and fiberscopes.

• 3.

  Laser tubes designed to be used with surgical lasers.

• 4.

  Wire-reinforced anode tubes. These tubes have a wire spirally embedded in the wall of the tube. This gives the tube flexibility while preserving the lumen (see Fig. 17.12 in Chapter 17 : Equipment).

  

Choosing the correct tracheal tube size is important in children to prevent significant complications and injuries to the airway. There are many different ways of estimating the appropriate ID size of the tracheal tube (see Table 19.5 ).

TABLE 19.5

Various Estimates of Which Tracheal Tube Size to Use in Children

Age	Khine 1997 (Khine et al. 1997)	Motoyama 1990 (Motoyama 1990)	Salgo 2006 (Salgo et al. 2006)
Birth to <6 months	3.0	3.0	3.0
6 months to <1 year	3.0	3.0	3.5
1 year to <18 months	3.5	3.5	3.5
18 months to <2 years	3.5	3.5	4.0
2 years to <3 years	3.5	4.0	4.0
3 years to <4 years	4.0	4.0	4.5
4 years to <5 years	4.0	4.5	4.5

Other techniques for estimating the size of a tracheal tube include age-based formulae, such as the following:

• Age/4 + 4 = uncuffed tracheal tube size

• Age/4 + 3.5 = cuffed tracheal tube size

Other formulas can be used to estimate depth of insertion, such as the following:

• Oral placement: depth of insertion in centimeters measured from the lips:

  • Tracheal tube ID × 3

  • (Age/2) + 12

• Nasal Placement: depth of insertion of a nasal tracheal tube measured at the nare:

  • (Age/2) + 15

  • (Height/10 × 1.2) + 5