Complications of Managing the Airway

Key Points

Serious complications of airway management result from not recognizing the degree of airway difficulty.
To minimize injury to the patient, the airway practitioner should examine the patient’s airway carefully, identify potential problems, devise a plan that involves the least risk for injury, and have a backup plan immediately available. Common sense should prevail at all times.
In the practice of airway management, errors of omission are more common than errors of commission. Errors of omission include failure to recognize the magnitude of a problem, make appropriate observations, and act in a timely manner. Errors of commission include actions such as trauma to the lips, nose, or laryngotracheal mucosa; forcing sharp instruments into areas in which they do not belong; or introducing air or secretions into regions of the body that will lead to further complications.
Many complications in airway management result from insufficient communication among the members of the medical team and improper coordination of the patients on the daily operating room schedule. A patient with known difficult airway (DA) problems should be scheduled at a time when the most experienced anesthesiologists and surgeons are available.
Delayed recognition of complications leads to delayed therapy. Inadequate monitoring, nonfunctional equipment, and untrained staff can contribute to airway catastrophes.
The overall risk of aspiration and regurgitation using the laryngeal mask airway (LMA) is about the same as for tracheal intubation when the indications and contraindications for the LMA are respected. The risk of aspiration, which is a consequence of the airway device’s design, should be weighed against the advantages of the LMA in cases of difficult intubation and ventilation.
Because of the increased risk associated with multiple attempts to perform any airway technique, a maximum of three attempts is recommended to minimize trauma to the airway.
Any airway device technique may cause movement and subsequent injury to the patient with an injured cervical spine.
A patent airway is an absolute requirement for safe anesthesia. Airway obstruction can occur at any time during administration of general anesthesia, particularly in prolonged operations or in patients with predisposing anatomic abnormalities. The most serious complication after extubation is the occurrence of acute airway obstruction.

Introduction

Airway management in anesthesia practice is often uncomplicated; however, complications, when they do occur, can have serious and long-lasting consequences. The Fourth National Audit Project (NAP4) of the Royal College of Anaesthetists and the Difficult Airway Society was established to estimate the incidence of major to disastrous complications of airway management and provide detailed information about the factors contributing to poor outcomes. In general, difficult airway and “cannot intubate, cannot oxygenate” (CICO) scenarios accounted for 39% of all serious events, followed by aspiration and extubation problems.

In the latest analysis of the American Society of Anesthesiologists (ASA) Closed Claims Project, 10% of recent claims concerning difficult intubation resulted in airway injury as compared to earlier claims, where airway injury was more common (34% of claims). ^, In general, most airway injuries are temporary, and death is a very rare outcome in routine practice ( Table 48.1 ). However, patients in more recent difficult tracheal intubation claims were significantly more likely to suffer death than patients in earlier difficult intubation claims (73% vs 42%).

Table 48.1

Severity of Injury and Standard of Care

Site of Injury (n)	SEVERITY OF INJURY		STANDARD OF CARE
Site of Injury (n)	Nonfatal n (%)	Fatal n (%)	Standard n (%)	Substandard n (%)
Larynx (87)	86 (99)	1 (1)	74 (96)	3 (4)
Pharynx (51)	46 (90)	5 (10)	29 (71)	12 (29)
Esophagus (48)	39 (81)	9 (19)	25 (60)	17 (40)
Trachea (39)	33 (85)	6 (15)	20 (63)	12 (38)
TMJ (27)	27 (100)	0	21 (100)	0
Nose (13)	13 (100)	0	11 (85)	2 (15)

TMJ , Temporomandibular joint.

Modified from Domino KB, Posner KL, Caplan RA, Cheney FW. Airway injury during anesthesia: a closed claims analysis. Anesthesiology. 1999;91:1703.

International studies exploring the incidence of complications during general anesthesia have been published in several countries, including the United Kingdom, ^, Australia, France, and Germany. The procedural problems and airway complications found in these studies are summarized in Table 48.2 . The rates of anesthesia-related death attributed to airway management problems cover a wide range: Biboulet and colleagues reported 25%, Braz and colleagues 55.5%, Charuluxananan and colleagues 21.3%, ^, Gibbs 15%, Kawashima and colleagues 7.9%, Newland and colleagues 20%, and Sprung and colleagues 80%.

Table 48.2

Procedural Problems and Airway Complications Encountered During General Anesthesia

Respiration	Equipment	Drugs	Management
Difficult intubation	Substandard monitoring	Missing drugs	Insufficient training
Difficult ventilation	Defective apparatus	Mix-up of drugs	No specialist on call
Failed intubation	Equipment not available	Drug overdose	Inadequate assistance
Aspiration		Drug hangover	Insufficient diagnosis
Laryngospasm			Nonfasted patient
Bronchospasm
Pneumothorax
Airway trauma
Airway obstruction
Respiratory depression

The inability to secure the airway and subsequent failure of oxygenation constitute a life-threatening complication. In the absence of major oxygen reserves, failure of oxygenation leads to hypoxia, followed by brain damage, cardiovascular breakdown, and death. As soon as oxygenation is no longer achievable, tissue damage is initiated, and irreversible injury occurs in a few minutes. The ultimate goal of airway management is oxygenation of the patient, not placement of an endotracheal tube (ETT).

Some complications are dramatic and immediately life-threatening (e.g., unrecognized esophageal intubation, tracheal rupture); some are severe and long-lasting (e.g., nerve injuries), and some are painful for the patient (e.g., sore throat). Good clinical practice aims to avoid all these complications.

In anesthesia practice, errors of omission are more common than errors of commission. Errors of omission include failure to recognize the magnitude of a problem, make appropriate observations, or act in a timely manner. Errors of commission include trauma to the lips, nose, or airway mucosa; forcing sharp instruments into areas where they do not belong; and introducing air or secretions into regions of the body that will lead to further complications. The primary goal of anesthesiologists is to ensure the safety and well-being of their patients, and they are usually careful in performing the technical aspects of their jobs. The most frequent cause of fatal errors in medical practice, especially in the field of airway management, is to ignore inadequate experience and skills and not call for help.

Complications With Mask Ventilation

Difficult mask ventilation is an underestimated aspect of managing a difficult airway (DA). Ventilation using a bag-mask breathing system is an essential skill for airway practitioners and may be life-saving for the patient. The CICO scenario represents the most severe form of airway difficulty. ^, Mask ventilation is used at the beginning of most cases of general anesthesia. Although the mask itself and the technique may seem benign, each can potentially cause problems.

The Sterilization Process

Many of the devices used to ventilate the patient and secure the airway are disposable, although some equipment is still reusable. All devices should be checked before use, and reusable items should be free of residual cleaning agents. Masks may have pinhole defects in their air-filled bladders, allowing air leaks or extravasation of cleaning fluid, which can cause severe irritation to the patient’s eyes or mucous membranes. ^, In one reported case, residual glutaraldehyde on an improperly rinsed laryngoscope blade caused life-threatening allergic glossitis resulting in massive tongue swelling. Care must be taken to thoroughly rinse the working channel of a flexible intubation scope (FIS) after cleaning; residual agents may drip from the working channel into the larynx or trachea, causing severe chemical burns.

Mechanical Difficulties

A mask is typically applied to a patient’s face before induction of general anesthesia. Preoxygenation of the patient is the first step in securing the airway. The mask should be applied during spontaneous breathing, before induction drugs are administered. During placement, direct contact of the rigid parts of the mask with the bridge of the nose or mandible should be avoided because they are at particular risk for compromised blood flow. Bruising and soft tissue damage may occur in these regions with excessive pressure, and pressure damage to the mental nerves as they exit the mental foramina has been implicated in lower lip numbness in two patients. Care must be taken to avoid contact with the eyes to prevent corneal abrasions, retinal artery occlusions, and blindness. As induction proceeds, firmer mask pressure and stronger lifting pressure on the angle of the mandible become necessary to maintain a tight mask fit and secure the airway. Pressure on the soft tissue of the submandibular region may obstruct the airway, especially in small children, or can damage the mandibular branch of the facial nerve, resulting in transient facial nerve paralysis.

During induction, the base of the tongue may fall back into the oropharynx and obstruct the airway. Oropharyngeal airways must be gently inserted into the mouth to avoid injury, such as broken teeth or mucosal tears. Improper placement may worsen airway obstruction by forcing the tongue backward. Equal care should be given to the placement of nasopharyngeal airways to avoid bleeding and epistaxis.

Before insertion of an oropharyngeal or nasopharyngeal airway, the oropharyngeal space should be enlarged. During conventional mask ventilation, the mandible is pressed against the maxilla, blocking condylar motion and hindering sufficient mouth opening and maximal extension of the base of the tongue. The mouth is opened and the mandible gently drawn forward and upward to displace the base of the tongue to a ventral position and increase the oropharyngeal space.

The lifting pressure applied to the angle of the mandible is sometimes sufficient to subluxate the temporomandibular joint (TMJ). Patients may experience persistent pain or bruising at these points or may have chronic dislocation of the jaw, which can cause severe discomfort. Positive airway pressure can force air into the stomach instead of the trachea, producing gastric distention, difficult ventilation, and an increased risk for regurgitation. The ability to achieve adequate mask ventilation should be assessed preoperatively.

The incidence of difficult mask ventilation is about 2 to 6 in 300. Independent risk factors for difficult mask ventilation are the presence of a beard, increased body mass index (BMI), edentulousness, age older than 55 years, history of snoring, sleep apnea or a high STOP-Bang score, limited mandibular protrusion, male gender, Mallampati class III or IV (used to predict ease of intubation), and airway masses or tumors. ^,

Other factors may make mask ventilation difficult or impossible, such as a large tongue, facial burns or deformities, stridor, or nasal polyposis. In these cases, it may be best to avoid mask ventilation and perform a rapid sequence induction or an awake intubation. Patients with trauma to the pharyngeal mucosa who are mask ventilated may be at risk for subcutaneous emphysema.

Laryngoceles may manifest as or cause upper airway obstruction during induction of anesthesia. Congenital factors contribute to development of laryngoceles, and persons who play wind instruments also may be at risk because high intrapharyngeal pressures can weaken soft tissue and cause laryngoceles in the lateral pharynx. ^,

Prolonged Mask Ventilation

Because mask ventilation offers no protection against regurgitation, the anesthesiologist should be vigilant for questionable airway noise, coughing, or bucking. Transparent masks allow visualization of the mouth and early identification of vomitus. Extra care should be taken to avoid undue pressure on vulnerable parts of the face. When continuous positive airway pressure (CPAP) is applied to patients with basilar skull fractures, pneumocephalus may occur. At least one case report identified positive airway pressure as the cause of bilateral otorrhagia.

Mask ventilation is relatively contraindicated in nonfasting patients, intestinal obstruction, Trendelenburg position, extreme obesity, tracheoesophageal fistula, and massive nasooropharyngeal bleeding, although it may be life-saving when other airway devices fail. Especially in pediatric cases, it may be necessary to avoid hypoxia.

Adequate monitoring during mask ventilation includes observation of chest movement, pulse oximetry, measurement of end-tidal carbon dioxide (EtCO ₂ ), and control of inspiratory pressure. In infants, a precordially placed stethoscope is recommended.

Complications With Supraglottic Airways

Laryngeal Mask Airway

Placing a laryngeal mask airway (LMA) and similar supraglottic airways (SGAs) correctly can be difficult in some patients. The mask may fold on itself, or the epiglottis may become entrapped in the laryngeal inlet of the mask. The epiglottis may be pushed down into the glottis, increasing work of breathing and producing coughing, laryngospasm, or complete airway obstruction. ^, Excess lubricant can leak into the trachea, promoting coughing or laryngospasm. Regardless of the problems encountered in placing the LMA, airway patency is usually maintained. An inadequate mouth opening (<1.5 cm), inadequate depth of anesthesia, insertion with an underdeflated cuff, inappropriate size of the LMA, inappropriate force during insertion, and inadequate volumes for cuff inflation can cause malpositioning of the LMA.

Numerous complications are associated with the LMA. Perhaps the greatest limitation is the inability of the LMA to protect against regurgitation of gastric contents and pulmonary aspiration. Because the LMA does not isolate the trachea from the esophagus, its use is risky when the patient has a full stomach or when high airway pressures are necessary for positive-pressure ventilation. The overall risk of aspiration and regurgitation using the LMA seems to be in the same low range as for tracheal intubation when the indications and contraindications for the LMA are respected. The risk of aspiration, which is a consequence of the design of the device, should be weighed against the advantages of the LMA in cases of difficult intubation and ventilation. Other complications have been reported with the use of the LMA. Their incidence and severity depend on the user’s skills and experience, depth of anesthesia, and anatomic or pathologic factors.

Failure to correctly place the LMA results from inadequate depth of anesthesia, suboptimal head and neck position, incorrect mask deflation, failure to follow the palatopharyngeal curve during insertion, inadequate depth of insertion, application of cricoid pressure (CP), or oral anatomic variations such as large tonsils. Laryngospasm and coughing result from inadequate depth of anesthesia, tip impaction against the glottis, or aspiration of gastric contents. A mask leak or the inability to ventilate the lungs results from inadequate depth of anesthesia, a malpositioned mask, inadequate mask size, or high airway pressure. Displacement of the LMA after insertion is caused by inadequate anesthesia depth, a pulled or twisted tube, or inadequate mask size.

Problems during recovery are removal of the LMA at an inappropriate anesthesia depth, laryngospasm, and coughing when oral secretions enter the larynx after cuff deflation, tube occlusion caused by biting, and regurgitation. Effects on pharyngolaryngeal reflexes such as laryngospasm, coughing, gagging, bronchospasm, breath-holding, and retching may be associated with LMA use.

The incidence of sore throat with the LMA is between 17% and 26%. The incidence of failed placement is 1% to 5%, although this rate tends to decrease with increasing operator experience. The LMA cuff is permeable to nitrous oxide and carbon dioxide, which can result in substantial increases in cuff pressure and volume during prolonged procedures. ^,

Several case reports cite edema of the epiglottis, uvula, posterior pharyngeal wall, and vocal cords; in the worst cases, these conditions have led to airway obstruction. Nerve paralysis (e.g., lingual, recurrent, hypoglossal, and glossopharyngeal), postobstructive pulmonary edema, tongue cyanosis, and transient dysarthria have been reported. Control of cuff pressure can reduce at least some of these complications. ^, Respiratory morbidity is reduced by up to 70% by using a cuff control device, and respiratory morbidity decreases even further if the cuff pressure does not exceed 25 cm H ₂ O. Other problems with the LMA include dislodgment, kinking, and foreign bodies in the tube, leading to airway obstruction.

Newer designs of the LMA were developed to increase comfort, handling, or safety in various situations. Second-generation LMAs combine the option of inserting a gastric tube through a separate drainage tube with an improved seal by design, which enables positive airway pressure ventilation at higher inspiratory pressures. Nonetheless, cases of gastric insufflation with malpositioned second-generation LMAs have been reported. ^,

The intubating laryngeal mask airway (ILMA) was designed to overcome unexpected difficult laryngoscopic intubation. Use of the ILMA has been successful in patients with DAs. ^, Tracheal intubation through the ILMA using specialized ETTs is easier than with the standard LMA, and the success rate for blind insertion of an ETT through the ILMA is greater than 90%. Branthwaite reported a case of esophageal perforation secondary to attempts at intubation using the ILMA in a patient with an undiagnosed high esophageal pouch leading to mediastinitis and the patient’s eventual death. Flexible scope-guided insertion of an ETT through an LMA has had the highest success rate for intubation and the lowest rate for damage of laryngeal structures. Modifications of the LMA have overall rates of complications similar to those already described. ^,

Classic contraindications to using an LMA include nonfasted patients, extreme obesity, necessity of high inspiratory pressures (>20 cm H ₂ O) in the presence of low pulmonary compliance or chronic obstructive pulmonary disease (COPD), acute abdomen, hiatal hernia, Zenker’s diverticulum, trauma, intoxication, airway problems at the glottic or infraglottic level, and thoracic trauma. Nevertheless, the LMA’s successors, particularly those with a channel for the insertion of a gastric tube, have led to more liberal use of LMA devices. Specifically, second-generation LMAs seem useful and safe for prolonged periods of use and for use in minor laparoscopic procedures, in the obese, in cesarean section, and in the prone position, provided the contraindications are heeded and there is adequate clinical expertise.

Other Supraglottic Airway Devices

Many devices are available for managing the airway at the supraglottic level: the cuffed oropharyngeal airway (COPA),the laryngeal tube (LT), the LaryVent (MedExNet, Amsterdam, the Netherlands), the glottic aperture seal airway (GO2 airway), the Cobra perilaryngeal airway (CobraPLA), and the King laryngeal tube suction (LTS). Overall, they seem to cause complications and physiologic alterations similar to those found with the LMA. ^, The devices were designed for separating the airway from the esophagus but do not efficiently protect the airway from regurgitation and aspiration. They share several advantages and disadvantages. Contraindications include nonfasted patients, gastroesophageal reflux, hiatal hernia, pregnancy, obesity, reduced pulmonary compliance, glottic or infraglottic stenosis, and mechanical obstruction of the oropharynx. Most complications arise from dislodgment, overinflating the cuff, or insufficient depth of anesthesia. Most of the devices were developed over the past few years, and acceptance in routine practice has varied. It should be emphasized again that in clinical and preclinical settings, cuff pressure control for any of these devices is paramount in reducing adverse sequelae.

Another concern is the wide range of available supraglottic devices. In addition to the limited storage space provided on the airway management cart, it seems impossible to maintain regular and sufficient training with all devices for all practitioners. Many complications in airway management are caused by operator inexperience and by inadequate or nonfunctional equipment. The recommendation for all anesthesiologists is to select a few devices that are used routinely or for which practitioners are well trained.

Esophageal-Tracheal Combitube and EasyTube

The esophageal-tracheal Combitube (Medtronic GmbH, Meerbusch, Germany) is an esophagotracheal, double-lumen airway designed for emergency use when standard airway management measures have failed. ^, Its use in elective surgery has also been reported. The Rüsch EasyTube (Teleflex Inc., Wayne, PA) is a dual-lumen airway with a similar design to the Combitube.

The Combitube is inserted blindly into the mouth and advanced to preset markings. The distal tube is usually positioned within the esophagus at this point. A distal cuff is inflated within the esophagus, and a large-volume proximal cuff is inflated inside the pharynx. Ventilation is then attempted through the proximal lumen because esophageal intubation occurs in approximately 96% of insertions. If ventilation through this lumen fails, ventilation is attempted through the distal lumen. The device is designed for single use, but a study of multiple uses of the Combitube found no problems arising from reprocessing. Another study warned against reuse because insufficient cleaning may lead to transmission of iatrogenic infections.

The 37-French (small adult) Combitube is not recommended for patients shorter than 120 cm, and the 41-French Combitube is not recommended for patients shorter than 150 cm. Disregarding these recommendations may cause serious esophageal injury. Further contraindications to using a Combitube are intact gag reflexes, ingestion of caustic substances, known esophageal disease, airway problems at the glottic or infraglottic level, and latex allergy.

The Combitube has major disadvantages because of its design. It can be used for a maximum of 8 hours (because tracheobronchial care is difficult through the Combitube), suctioning of the trachea is not possible with the device in the esophageal position (which may be problematic in the case of copious tracheal secretions), it may injure pharyngeal and esophageal soft tissues, and no pediatric sizes are available.

Various complications have been reported with use of the Combitube. In two patients, the device was inserted too far, causing the large pharyngeal cuff to lie directly over the glottis and obstruct the upper airway. This was easily resolved by partially withdrawing the Combitube until breath sounds were auscultated. Tongue discoloration has been reported while the pharyngeal cuff was inflated, although this usually resolves immediately without further adverse sequelae after the cuff is deflated. The Combitube has also been linked to glossopharyngeal and hypoglossal nerve dysfunction, esophageal rupture, subcutaneous emphysema, pneumomediastinum, pneumoperitoneum, and tracheal and esophageal injury and bleeding. Esophageal lacerations are most likely caused by incorrect use; in both referenced cases, the distal cuff was overinflated, and the larger Combitube (41 French) was used in a small patient. When compared with intubation with a standard ETT, the EasyTube and Combitube show a higher incidence of minor trauma. Despite their disadvantages, the Combitube and the EasyTube are widely accepted as devices for managing the DA.

Complications With Intubation

Tracheal Intubation

Laryngoscope Modifications and Rigid Optical Instruments

Laryngoscopes are designed for visualization of the vocal cords and for placement of the ETT into the trachea under direct vision. The two main types are the curved Macintosh blade and the straight blade (e.g., the curve-tipped Miller blade or the straight-tipped Wisconsin or Foregger blades). All blades are available in different sizes for patients of every age. The main injury caused by using laryngoscopes is damage to the teeth. In cases of inadequate visualization of the glottis, a change of the patient’s head position may lead to success. In some cases, a blade of inadequate size is responsible for intubation failure. Backward-upward-rightward pressure (BURP) on the thyroid cartilage or optimal external laryngeal manipulation (OELM) may move the glottis into the line of vision and facilitate intubation (see Chapter 20 ). ^,

Obtaining a view of the glottis with a conventional laryngoscope requires optimal positioning of the patient. With flexible scope intubation (FSI), positioning is not an issue, and damage to the teeth is less likely. Similarly, with video-assisted laryngoscopy (VAL), a video image of the oropharynx and the laryngeal inlet is transmitted from the camera in the tip of the blade and allows laryngoscopy and intubation in positions other than the sniffing position. The advantages of these instruments help to reduce the number of difficult or failed intubations and the incidence of dental damage. In studies on manikins or patients with normal airways, these devices have been demonstrated to perform better than or equal to the Macintosh laryngoscope, and other studies have demonstrated successful intubation of patients with known or suspected DAs. ^,

Although visualization of the glottis is easier with VAL, insertion of the ETT can be difficult. The monitor view reveals only the laryngeal inlet, and advancing the tube into the larynx may require an introducer or a built-in guiding channel, which can make the instrument bulky and the technique more complicated than with a conventional laryngoscope. Several cases of pharyngeal injuries have been reported with the rigid GlideRite stylet of the GlideScope, and palatal perforation has been reported with the McGrath video laryngoscope. Increased awareness of potential complications, better training and supervision, and appropriate equipment and patient selection can reduce the incidence of complications. In addition, choosing a tube with a flexible anterior tip (such as the Parker Flex-Tip) may reduce complications.

Laryngoscopy requires deep anesthesia because it causes strong stimulation of physiologic reflexes, and respiratory, cardiovascular, and neurologic adverse effects are possible. Hypertensive patients, pregnant patients with hypertension, and patients with ischemic heart disease are particularly at risk. Deep anesthesia, application of topical anesthetics, prevention of the sympathoadrenal response with drugs such as opioids or intravenous (IV) lidocaine, and minimizing mechanical stimulation can attenuate the adverse effects. Multiple case reports exist for awake intubations using VAL under topical anesthesia.

Rigid optical instruments such as the Bonfils retromolar intubation fiberscope and its modifications, the Bullard laryngoscope, and the intubation tracheoscope are not as commonly used in anesthesiology. They require skilled handling, and experience should be gained in routine cases to apply to DA situations. The rigid intubation tracheoscope, a familiar device in otorhinolaryngologic surgery, has special indications and may be useful in the hands of anesthesiologists.

The disadvantages of these instruments are a relatively closed view through the tube, a high risk of damage to the teeth and laryngeal structures, possible perforation of the hypopharynx, and risk of aspiration. High-flow oxygen insufflation through a port can induce subcutaneous cervical and facial emphysema.

Traumatic Intubation

Despite optimal positioning of the head and neck, the glottis is sometimes impossible to visualize, even in patients without obvious predisposing features. Difficult intubations, particularly unexpected ones, are often traumatic. In a case of difficult intubation, the practitioner tends to increase the lifting forces of the laryngoscope blade, which may damage the intraoral tissues and osseous structures. Continuing attempts to intubate the patient many times without changing the approach or technique leads to traumatic intubation. Use of increasing force may cause swelling, bleeding, or perforation, resulting in a more difficult intubation and possibly leading to a CICO situation. A maximum of three attempts to achieve intubation using a laryngoscope is recommended. If intubation fails after three attempts, another airway-securing technique should be used following a DA algorithm.

Lip Injury

Lip injuries, which typically occur on the upper lip, include lacerations, hematomas, edema, and teeth marks. They are usually caused by inattentive laryngoscopy performed by inexperienced practitioners, the laryngoscope blade, and the teeth. Although these injuries are annoying to the patient, they are usually self-limited.

Dental Injury

The incidence of dental injury associated with anesthesia is greater than 1 case in 4500 procedures. A prospective observational study reported the rate of any dental damage, including enamel fracture, to be 25%. Maxillary central incisors are most at risk; 50% of these injuries happen during laryngoscopy, 23% after extubation, 8% during extubation, and 5% in the context of regional anesthesia. With the use of an SGA, the incidence of dental injuries is up to six times lower than with laryngoscopy. However, the use of SGAs and oropharyngeal airways can result in dental injury. With insufficient anesthetic depth, biting against the device is possible, causing injury. Dental injuries are most common in small children; in patients with periodontal disease (in which structural support is poor), fixed dental work (e.g., bridges or caps), protrusion of the upper incisors (i.e., an overbite), or carious teeth (poor preexisting dental status); and in cases of difficult intubation. Preexisting dental pathology, the most significant preexisting risk factor, should be explored, and all loose, diseased, chipped, or capped teeth must be documented in the chart before anesthesia induction and intubation. ^,

The patient must be advised of the risk of dental damage and should be consented for removal of very loose teeth. Tooth guards may be used, but they can be awkward and obstruct visualization of the glottis, although they do not seem to significantly prolong time to intubation.

Fragments of chipped or partially broken teeth and completely avulsed teeth should be located and retrieved. Care should be taken to ensure that no foreign bodies slip into the pharynx to later become lodged in the esophagus or the respiratory tract. Tooth aspiration may cause serious complications requiring rigid or flexible bronchoscopy for removal. Avulsed teeth should be saved in moist gauze or in normal saline without cleaning them. With a rapid response from an oral surgeon or a dentist, an intact tooth can often be reimplanted and saved. The optimal time is within the first hour; thereafter, reimplantation success diminishes with increasing time.

Tongue Injury

Massive tongue swelling, or macroglossia, has been reported in adult and pediatric patients. ^, Macroglossia can occur with a bite block or oral airway in place, with soft tissue compression of the chin, or with no protective device. A risk factor is substantial neck flexion during prolonged surgery. Macroglossia results from obstructed venous and lymphatic drainage of the tongue, and it has been associated with angiotensin-converting enzyme inhibitors. The ETT may severely compromise the circulation on one side of the tongue, causing hemimacroglossia. One report described the sudden onset of tongue swelling after prolonged surgery to repair a cleft palate, during which the tongue was retracted extensively. Obstruction of the submandibular duct by an ETT may lead to massive tongue swelling. Reduced sense of taste, tongue cyanosis, or loss of tongue sensation is possible after compression of the lingual nerve or lingual artery during forced intubation or because of an oversized, malpositioned, or overinflated SGA.

Injury to the Uvula

Injury to the uvula is usually associated with the use of ETTs, oropharyngeal and nasopharyngeal airways, or SGAs, and with overzealous blind use of a suction catheter. The results of damaging the uvula are edema and necrosis. Sore throat, odynophagia, painful swallowing, coughing, foreign body sensation, and serious life-threatening airway obstruction have been reported.

Pharyngeal Mucosal Injury

A postoperative sore throat (POST) likely represents a broad constellation of signs and symptoms. The incidence of POST after intubation (34.3%) is higher than after SGA use (21.5%) and after face-mask ventilation. ^, The incidence of POST associated with the use of the Combitube was 48%. Aggressive suctioning is probably a contributing factor. The incidence is substantially higher in women and in patients undergoing thyroid surgery. No correlation is seen with factors such as age, use of muscle relaxants, type of narcotic used, number of intubation attempts, or duration of intubation. Smaller ETTs, lower cuff inflation pressures, topical treatment with local anesthetics, and inhalation of steroids have a beneficial impact on POST. Pain on swallowing usually lasts no more than 24 to 48 hours and can be relieved in part by having the patient breathe humidified air.

Laryngeal Trauma and Injury to the Vocal Cords

Trauma to the larynx may occur after tracheal intubation, depending on the skill of the practitioner and the degree of difficulty. In one large study, 6.2% of patients sustained severe lesions, 4.5% had hematoma of the vocal cords, 1% had hematoma of the supraglottic region, and 1% sustained lacerations and scars of the vocal cord mucosa. Recovery is typically prompt with conservative therapy. Hoarseness may appear as late as 2 weeks postoperatively.

Granulomas usually occur as a complication of long-term intubation ( Fig. 48.1 ); however, a small but significant number of patients sustain laryngeal injuries during short-term intubation. Intubation can cause various degrees of laryngeal trauma, including thickening, edema, erythema, hematoma, and granuloma of the vocal folds. ^, Injuries of the laryngeal muscles and suspensory ligaments are possible ( Fig. 48.2 ). The larynx should be inspected for injury before insertion of the ETT to document and treat preexisting lesions. Anesthesiologists should be vigilant in all cases of hoarseness, and patients with sustained postoperative hoarseness should be examined by an otorhinolaryngologist.

Fig. 48.1, Granuloma on the anterior aspect of the left vocal cord after endotracheal intubation.

Fig. 48.2, Injury to the anterior commissure of the vocal cords in a child.

Arytenoid dislocation and subluxation have been reported as a rare complication of intubation. Associated factors include traumatic and difficult intubations, repeated attempts at intubation, extubation with an inflated cuff (e.g., self-extubation), intubation using blind techniques (e.g., light-guided intubation or retrograde intubation), or use of the McCoy laryngoscope. Early diagnosis and conservative or operative treatment are necessary, because fibrosis with subsequent malpositioning and ankylosis may occur after 48 hours ( Fig. 48.3 ).

Fig. 48.3, Interarytenoid fibrosis after intubation. A fibrotic lesion has developed between the arytenoid cartilages after prolonged intubation.

The vocal process of the arytenoid is the most common site of injury by the ETT because it is positioned between the vocal cords. Granuloma formation most commonly occurs at this site. The degree of injury worsens with increasing tube size and duration of intubation.

There have been numerous case reports of unilateral or bilateral vocal cord paralysis after intubation, which is usually temporary. One report associated vocal cord paralysis with use of ethylene oxide to sterilize ETTs. Hoarseness occurs with unilateral paralysis, whereas respiratory obstruction may occur with bilateral paralysis. The most likely source of injury is an ETT cuff malpositioned in the subglottic larynx with pressure on the recurrent laryngeal nerve. ^, Permanent voice change after intubation because of external laryngeal nerve trauma has been reported in up to 3% of patients undergoing surgery at sites other than the head or neck. The incidence may be decreased by avoiding overinflation of the ETT cuff and by placing the ETT cuff at least 15 mm below the vocal cords.

Eroded vocal cords may adhere to one another, eventually forming synechiae. This is a potential problem when airflow between the vocal cords has been compromised as a result of tracheostomy. Surgical correction is usually necessary.

Tracheobronchial Injury

Tracheal injury has many causes, including an overinflated ETT cuff, inappropriate ETT size, or malpositioning of the ETT tip, laryngoscope, stylet, tube exchanger, or related equipment. Predisposing factors include anatomic abnormalities, blind or hurried intubation, inadequate positioning, poor visualization, and, most commonly, inexperience of the practitioner. The presence of an ETT in the trachea may lead to edema, desquamation, inflammation, and ulceration of the airway ( Figs. 48.4 and 48.5 ). The severity of the injury may be related to the duration of intubation, although this relationship is not well established. Any irritating stimulus, such as pressure from an oversized ETT, dry inhaled gases, allergic reactions to inhaled sprays, or chemical irritation from residual cleaning solutions, can initiate an inflammatory response and cause mucosal edema in the larynx or trachea. Edema after extubation decreases the lumen diameter and increases airway resistance. Small children are most susceptible to this problem, with the sudden increase in airway resistance leading to postintubation croup; almost 4% of children 1 to 3 years old develop croup after tracheal intubation. ^, Microcuff pediatric ETTs (Kimberly Clark, Atlanta, GA) have improved tracheal sealing characteristics, providing an adequate seal with cuff pressures greater than 10 cm H ₂ O in children; their use will likely decrease the incidence of some of the previously mentioned problems. ^,

Fig. 48.4, Subglottic stenosis. An endotracheal view through the vocal cords shows subglottic stenosis after long-term intubation.

Fig. 48.5, Ulcerative lesion in the area of the left vocal cord after long-term intubation.

Mechanical trauma may result from sharp objects within the trachea, such as a stylet tip that extends beyond the length of the ETT. Tracheal ruptures, especially after emergency intubation, have been reported. Bronchial rupture caused by an airway exchange catheter (AEC) has also been described.

ETT cuffs inflated to a pressure greater than that of the capillary perfusion may devitalize the tracheal mucosa, leading to ulceration, necrosis, and loss of structural integrity. Ulceration can occur at even lower cuff pressures in hypotensive patients. The need for increasing cuff volumes to maintain a seal is an ominous sign that heralds tracheomalacia. Massive gastric distention in an intubated patient may signal the presence of a tracheoesophageal fistula as the cuff progressively erodes into the esophagus. Any patient with more than 10 mL of blood in the ETT without a known cause should be assessed for a tracheocarotid fistula. The various nerves in this region of the neck are also at risk. Erosion of the ETT into the paratracheal nerves may result in dysphonia, hoarseness, and laryngeal incompetence. Tracheomalacia results from erosion confined to the tracheal cartilages. The ETT cuff should only be inflated as much as necessary to ensure an adequate airway seal. When nitrous oxide is used during a lengthy surgical procedure, pressure in the cuff should at least be periodically checked by a manometer or using a cuff pressure control device. In the presence of 70% nitrous oxide, intracuff pressures increase to levels that are potentially high enough to cause tracheal ischemia in only 12 minutes on average. ETT cuff pressure should not exceed 25 cm H ₂ O. Increasing cuff pressure caused by surgical manipulations can also be observed and prevented by using a manometer or cuff pressure control device.

Tracheal intubation may erode the tracheal mucosa, leading to scar tissue, which ultimately retracts and leads to tracheal stenosis. The reported incidence of granulomas is 1 case in every 800 to 20,000 intubations. ^, They are more common in women than in men and occur rarely in children. Avulsion of mucous membranes may also result from electrodes wrapped around the ETT for laryngeal nerve stimulation because these provide sharp edges ( Fig. 48.6 ). The most common site of erosion is along the posterior laryngeal wall, where granulation tissue easily overgrows. Side effects of granulomas include cough, hoarseness, and throat pain. The growths may be prevented by minimizing the trauma associated with laryngoscopy and intubation. When granulomas occur, surgical excision is usually required.

Fig. 48.6, An endotracheal view shows avulsion of the mucous membranes caused by wrapping of the endotracheal tube with stimulation electrodes for neurosurgery in a 2-year-old child.

Membranes and webs may eventually replace tracheal and laryngeal ulcers. These growths are commonly thick and gray. Care should be taken while intubating patients with these lesions because inadvertent detachment may result in respiratory obstruction or bleeding into the airway. With time, the inflammatory process associated with laryngeal ulcers may extend to the laryngeal cartilage. If this occurs, the cartilage may become inflamed (i.e., chondritis) or softened (i.e., chondromalacia).

Several months after prolonged tracheal intubation, tracheal stenosis and fibrosis may occur. This usually represents the end stage of a progression from tracheal wall erosion to cartilaginous weakening to healing with fibrosis. Stenosis typically occurs at the site of an inflated cuff, although it may occur at the location of the ETT tip. Symptoms include a nonproductive cough, dyspnea, and signs of respiratory obstruction. Dilation of the stenosis is curative in its early stages. However, surgical correction may be necessary after the tracheal lumen has been reduced to 4 to 5 mm in adults. ^,

Supraglottic complications induced by long-term intubation may be prevented by early tracheostomy. There is no evidence supporting an ideal time for tracheostomy in long-term ventilated patients.

Barotrauma

Barotrauma results from high-pressure distention of intrapulmonary structures. High-flow insufflation techniques in which small catheters are used distal to the larynx are most often associated with barotrauma. These problems are common in microlaryngeal surgery when jet ventilation is used. Direct impingement of the catheter tip on the tracheal mucosa may also cause barotrauma. Edema or hematoma may occur if the jet of air strikes the mucosa of the larynx or the vocal cords, leading to laryngospasm. When air leaks into the peribronchial tissues, it can traverse into the subcutaneous space, the lung interstitium, or the pleural and pericardial cavities. Pneumomediastinum or tension pneumothorax and possibly cardiac tamponade are the results, and chest tubes may be necessary. Progressive accumulation of air may cause loss of pulmonary compliance and loss of ventilatory volume; if the accumulation is large enough, cardiopulmonary compromise and impossible ventilation may result. Safety mechanisms should be in place to prevent high-pressure airflow in the event that intrapulmonary pressures become excessive. For diseased pulmonary tissue, the lowest possible airway pressure should be used to prevent parenchymal blowout. This advice also applies to patients with blunt thoracic trauma who have subcutaneous emphysema; they should be presumed to have a bronchial leak unless proved otherwise. Barotrauma may also result from upper airway obstruction during jet ventilation.

Nerve Injuries

Laryngoscopy and cuffed SGA devices may cause temporary or permanent nerve injury. Lingual, recurrent, hypoglossal, and glossopharyngeal nerve paralysis have all been described for LMA devices, and neuropraxia with weakness, numbness, or paralysis of the tongue can occur after laryngoscopy, presumably caused by pressure on the hypoglossal nerve. ^, Damage to the internal branch of the superior laryngeal nerve resulting in supraglottic anesthesia may occur during a difficult intubation and may lead to aspiration. Malposition of the cuff or tube may be one reason for nerve injury. Ahmad and Yentis postulated that lingual nerve injury may occur where the nerve distal to its gingival branch is compressed by the LMA tubing against the side of the tongue.

Spinal Cord and Vertebral Column Injury

Airway management techniques such as chin lift, jaw thrust, and direct laryngoscopy (DL) transmit movement to the cervical spine. When a patient’s neck is fused, adequate neck extension may be impossible to obtain. Attempting to hyperextend the neck of these patients may result in cervical fractures and quadriplegia. A head that is fixed in a cervical collar or halo does not allow neck extension and limits the successful use of DL. Using an FIS to assist intubation should be considered in these cases. If immediate intubation is necessary, patients with acute cervical spine fractures may be carefully intubated with manual in-line stabilization, whereby the head is protected against excessive movement by a second person. C1 and C2 fractures seem to be particularly vulnerable because any degree of extension or flexion may compromise spinal cord function. Between 10% and 25% of spinal cord injuries occur because of improper immobilization of the vertebral column after trauma, and neurologic deterioration has been associated with DL in patients with cervical spine injury.

Several conditions, such as Down syndrome and rheumatoid arthritis, are associated with atlantoaxial instability. Excessive neck extension in a patient with an undiagnosed Arnold-Chiari malformation may cause worsening of cerebellar tonsil herniation. Patients with underlying diseases such as connective tissue disorders, lytic bone tumors, and osteoporosis should be intubated carefully, and extreme neck extension should be avoided in every patient because of loss of muscle tone by curarizing drugs. A range-of-motion test and an assessment of neck extension should be performed before inducing anesthesia. A case of quadriplegia after bag-mask ventilation, DL, and cricothyrotomy in a patient with an unrecognized cervical spine injury was reported. A review of the records of 150 patients with unstable cervical spine injury found a 1.3% incidence of neurologic deterioration after elective surgery with tracheal intubation. Awake FSI should be considered when neck extension cannot be achieved without the risk of damage and time is not crucial. It is considered the safest method for airway management in patients with cervical spine injury. In cases where awake FSI is not feasible (e.g., uncooperative patients and small children) or attempts are unsuccessful, the use of VAL may be an option as these devices minimize cervical spine movement during intubation. ^, Alternatively, an SGA may be used to manage the airway.

Eye Injuries

The ASA Closed Claims Project reported that eye injuries were responsible for 3% of all claims; of these, 35% were related to corneal injuries, with corneal abrasions being the most common eye complication. Corneal abrasions are primarily caused by a face mask being placed on an open eye or by the eyelids not being completely closed during anesthesia. ^, Jewelry, identification cards, and loose-fitting watch bands have been implicated in scratching the cornea. A stethoscope hanging from the neck of a clinician can fall forward and strike the patient’s eyes or forehead. Other factors that may cause cornea abrasion may not be completely controllable. However, guidelines for the prevention of eye injuries consist of vigilance on the part of the practitioner and early application of adhesive tape over closed eyelids and the use of lubricants containing an aqueous methylcellulose solution or viscous gel for high-risk surgery (e.g., head and neck surgery, prone or lateral positioning). The incidence of corneal injury varies widely between studies and ranges between 1 in 1000 to 1 in 10,000.

Although most corneal injuries typically heal within 24 hours, they are usually painful and can lead to corneal ulceration. An immediate ophthalmologic consultation is recommended. Local anesthetics should not be applied because they can delay regeneration of the epithelium and may promote keratitis. Treatment consists of allowing the injured eye to rest by using an eye patch and applying an antibiotic ointment.

Temporomandibular Joint Injuries

TMJ anatomy is special in that one side cannot be moved without the other side. Both joints represent a functional unit, and injuries to one TMJ affect the other side. Opening the mouth is a combination of rotary and translational movement in the joint. The rotary movement allows only a mouth opening of about 25 mm; maximal opening is achieved by the translational movement. Pathologic changes such as bone cysts, rheumatoid arthritis, and atrophy of the mandible as a result of age can reduce joint mobility and may lead to fractures. Rupture of the lateral ligament is possible. TMJ injuries are caused by increasing forces during laryngoscopy to optimize the view of the vocal cords. Limited mouth opening, pain in the joint, lateral deviation of the mandible (i.e., unilateral luxation), protrusion of the mandible (i.e., bilateral luxation), and lockjaw (i.e., fixation after joint luxation) may occur. Most reported cases of TMJ injury were not associated with a DA.

Nasotracheal Passage

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