Anesthesia for Otolaryngologic and Head-Neck Surgery

Synopsis of Ear, Nose, and Throat Anatomy

Figs. 70.1 to 70.4 illustrate various aspects of ENT anatomy. The oropharynx extends from the uvula to the hyoid bone. The hypopharynx extends from the hyoid to the cricoid cartilage. The glottis includes both vocal cords, the anterior commissure, and the posterior intraarytenoid area. The subglottis extends 5 mm (anteriorly) to 10 mm (posteriorly) below the apex of the vocal cords (also known as vocal folds). The larynx, essential to respiration and speech, has a clinically important glottic closure reflex mediated through bilateral superior laryngeal nerves. This reflex serves to protect the airway against aspiration. For example, swallowing activates this protective reflex. On occasion this protective reflex can be problematic because when sustained spasm of the glottic muscles (a condition known as laryngospasm) occurs, gas exchange cannot take place. Laryngospasm is associated with light anesthesia and is frequently triggered by blood or secretions irritating the vocal cords, as often occurs after septoplasty and rhinoplasty surgery. Because it can make ventilation impossible, laryngospasm may constitute a true anesthetic emergency (see later).

Branches of the right and left vagus nerves innervate the larynx. The right vagus nerve gives rise to the right recurrent laryngeal nerve, whereas the left vagus nerve gives rise to the left recurrent laryngeal nerve. The two recurrent laryngeal nerves provide motor innervation to all the intrinsic muscles of the larynx, except the cricothyroid and inferior pharyngeal constrictor muscles, which are innervated by the branches of the superior laryngeal nerves. The internal laryngeal nerve is the internal branch of the superior laryngeal nerve (see Fig. 70.3 ). It descends to the thyrohyoid membrane, pierces it along with the superior laryngeal artery, and provides sensory innervation to the larynx down to the vocal cords. Sensory innervation below the vocal cords and to the upper trachea is supplied by the recurrent laryngeal nerves (see Fig. 70.3 ).

Injury to the recurrent laryngeal nerves, which supply most of the laryngeal intrinsic muscles, is a feared but often preventable complication in thyroid surgery and a host of other procedures, including tracheal intubation. If the damage is unilateral, the patient may present with hoarseness from unilateral loss of vocal cord abduction occurring in conjunction with intact cricothyroid-mediated adduction. This situation causes the affected vocal cord to assume a paramedian position. Bilateral nerve damage can result in dyspnea, stridor, and even full airway obstruction from bilateral vocal cord paramedian positioning. Such patients may require a tracheostomy. Intraoperative neuromonitoring is often used to reduce the chance of injury to the recurrent laryngeal nerves, especially in thyroid surgery.

Preoperative Evaluation for Ear, Nose, and Throat Surgery

Although the preoperative evaluation of the surgical patient is discussed in detail in Chapter 31 , a few issues are especially pertinent to ENT cases. Many ENT patients, especially those with malignant head and neck diseases, have histories of prolonged tobacco and alcohol use, whereas many others suffer from obesity or obstructive sleep apnea (OSA). Patients with chronic airway obstruction may develop pulmonary hypertension, sometimes leading to right-sided heart failure (cor pulmonale). A history of hoarseness may signal recurrent laryngeal nerve injury or worse, whereas the presence of stridor is always a cause for immediate concern. In cases involving the airway, the anesthesiologist and surgeon frequently review available radiographic and video studies to establish an airway plan collaboratively. A history of head and neck radiation for malignancy treatment frequently makes intubation difficult because the structures may become tough and fibrotic (“like wood”), yet they are predisposed to bleeding with instrumentation. A history of snoring may signal that the patient has undiagnosed sleep apnea and is prone to airway obstruction.

ENT cases frequently involve geriatric patients, many of whom are at a high risk for postoperative delirium and cognitive dysfunction. Although many ENT procedures involve infrequent risk, some of the large head and neck operation sare considered to have “intermediate” surgical risk. A preoperative resting 12-lead electrocardiogram (ECG) is recommended for patients with known coronary heart disease, peripheral arterial disease, or cerebrovascular disease who are undergoing such procedures. Additionally, patients with a history of heart failure, diabetes mellitus, or renal failure who are undergoing intermediate-risk operative procedures benefit from an ECG. Preoperative ECG testing is not indicated in asymptomatic persons undergoing infrequent-risk procedures.

A preoperative endoscopic airway examination can be performed in selected patients. This technique uses an ordinary flexible fiberscope usually used for awake endotracheal intubation to conduct a quick transnasal laryngoscopic examination using topical anesthesia. This examination allows the clinician to determine whether a problematic laryngeal disorder exists, such as supraglottic lesions that would not be apparent by ordinary means. The procedure requires minimal time and patient preparation, and it is well tolerated by patients. A review by Rosenblatt provides ample details.

Airway Management in Otolaryngology

Both easy and difficult airways are frequently encountered in ENT anesthesia. The American Society of Anesthesiologists (ASA) Difficult Airway Algorithm (or similar algorithm), should ordinarily be a starting point for nearly all aspects of ENT airway management. To a large extent, the specific airway management techniques chosen depend on clinical circumstances, the airway management skills and preferences of the anesthesiologist and surgeon, and the available equipment.

The following general management options exist: (1) general endotracheal anesthesia; (2) general anesthesia using a supraglottic airway (SGA) device (e.g., laryngeal mask airway [LMA]); (3) general anesthesia using an ENT laryngoscope (to expose the airway) in conjunction with jet ventilation; (4) use of intermittent apnea; (5) general anesthesia using the patient’s natural airway, with or without adjuncts such as jaw positioning devices or nasopharyngeal airways; and (6) local anesthesia in conjunction with intravenous sedation, with the patient breathing spontaneously. The first option is doubtless the most popular. However, the technique chosen and implemented depends on factors such as the perceived difficulty of intubating the trachea with ordinary methods. Evaluation of the airway in this particular respect is also discussed in Chapter 44 .

The airway can become obstructed for many reasons. Examples include the following: aspirated foreign bodies; infections such as epiglottitis, diphtheria, or Ludwig angina; laryngospasm; tumors and hematomas impinging on the airway; trauma to the airway; OSA; tonsillar hypertrophy; and airway edema (e.g., from anaphylaxis, prolonged laryngoscopy, or smoke inhalation or burn injury). In most cases, airway management is determined after a discussion between the anesthesia and surgical teams.

Most patients undergoing ENT surgery have their airway managed by tracheal intubation. Although under ordinary circumstances tracheal intubation is straightforward, patients whose tracheas are expected to be difficult to intubate can be identified and usually managed with techniques such as videolaryngoscopy or fiberoptic intubation. A key decision in such cases is whether the tracheal intubation should be performed with the patient awake or following the induction of general anesthesia. Another important decision is what tools or interventions to employ in the event that difficulty with ventilation or intubation is encountered. In exceptional cases, a tracheostomy using local anesthesia must be performed.

Patients for ENT surgery are often managed using an ordinary polyvinyl chloride (PVC) endotracheal tube (ETT), but microlaryngeal tubes (MLTs), laser tubes, and wire-reinforced tubes are also frequently used. Reinforced tubes have the advantages that they are unlikely to kink and they fit especially well into tracheostomy stomas because of their excellent flexibility. Selection of laser-resistant ETTs should be made based on the material appropriate to the type of laser being used for the procedure. In addition, the tracheal cuff can be filled with saline dyed with methylene blue to allow immediate detection of laser injury to the cuff. Practical considerations in this setting start with the fact that the tube must be adequately secured using tape or other means; some maxillofacial surgeons suture the tube to the side of the mouth or even tie the tube to the teeth with wire. In addition, the ETT cuff pressures ordinarily must be kept less than 25 mm Hg to avoid ischemic damage to the tracheal mucosa. When nitrous oxide is used, cuff pressures gradually increase as nitrous oxide enters the cuff by diffusion. This is of particular concern in surgical procedures of long duration, such as free-flap surgery.

Before attempting tracheal intubation, its difficulty using direct laryngoscopy can often be predicted. The 11-point airway assessment tool included with the 2003 ASA Difficult Airway Algorithm is an excellent source of information and advice. In addition, following the completion of tracheal intubation, the difficulty (if any) encountered should be summarized. The Intubation Difficulty Scale (IDS) introduced by Adnet and associates can be useful. IDS is a numeric score indicating overall intubation difficulty based on seven descriptors associated with intubation difficulty: number of supplementary intubation attempts, number of supplementary operators, alternative techniques used, laryngoscopic grade, subjective lifting force, the use of external laryngeal manipulation, and the characteristics of the vocal cords.

Most endotracheal intubations are achieved using traditional Macintosh and Miller laryngoscopes, although several alternative laryngoscopes have been advocated. When the view at laryngoscopy is suboptimal, the use of introducers such as the Eschmann stylet (gum elastic bougie) can sometimes be very helpful. It is used as follows: when a poor laryngoscopic view of the glottic structures is obtained, the introducer should be inserted into the patient’s mouth and gently advanced through the glottic opening (in the case of a grade II view) or anteriorly under the epiglottis (in the case of a grade III view). Subtle clicks resulting from the introducer passing over the tracheal rings help confirm proper placement of the introducer. With the introducer held steady, one then “railroads” a tracheal tube over the introducer into the glottis.

Video laryngoscopes such as the GlideScope (Verathon, Bothell, WA), the McGrath (Covidien, Mansfield, MA) video laryngoscope, the Storz video laryngoscope (Karl Storz, Tuttlingen, Germany), and the Pentax AWS (Hoya Corporation, Tokyo) have become particularly valuable, especially in patients with an “anterior” larynx or in patients with cervical spine immobilization.

As discussed in Chapter 44 , awake endotracheal intubation involves ETT insertion in a conscious or lightly sedated patient. It is usually performed because endotracheal intubation during general anesthesia is judged to be too risky. Some concerns may reflect possible difficulties with ventilation or endotracheal intubation or possible aspiration of gastric contents. Although fiberoptic intubation using topical anesthesia is the most common approach to awake endotracheal intubation, other methods include awake blind nasal intubation using an Endotrol (or similar) ETT or the use of a Macintosh, Miller, GlideScope, or other laryngoscope with topical anesthesia. Certain airway blocks can be used in addition to topical anesthesia. These are discussed in Chapter 44 .

The use of fiberoptic intubation for the airway management of patients undergoing otolaryngologic surgery is popular because this technique works well in the presence of many kinds of airway disease. Although fiberoptic intubation can often be safely performed during complete general anesthesia, many clinicians opt to perform this technique using topical anesthesia with the patient only lightly sedated (awake fiberoptic intubation), depending on the skill level of the anesthesiologist, the cooperation of the patient, and the severity of the pathologic process. A central consideration behind the choice of “awake” versus “asleep” fiberoptic intubation is the safety margin an awake technique allows: if intubation is not successfully accomplished, the patient’s ability to maintain his or her own airway remains intact. In addition, during awake intubation, airway reflexes are generally maintained sufficiently to guard against pulmonary aspiration, an important point in patients with a high risk of aspiration of gastric contents. Patients who have recently eaten and have undergone trauma are at especially high risk.

Awake endotracheal intubation is not synonymous with fiberoptic intubation. Awake intubation can be ac-complished safely using many other airway devices. Other possible options for awake intubation include, but are not limited to, direct laryngoscopy with Macintosh and Miller laryngoscopes, blind nasal intubation, use of a GlideScope or other video laryngoscope, use of a lighted stylet, and so on.

Typically, in intubation of the trachea in an awake patient, the airway is initially anesthetized with gargled and atomized 4% lidocaine. Superior laryngeal and transtracheal blocks are occasionally also employed. In addition, judicious sedation is usually administered. Midazolam, fentanyl, remifentanil, ketamine, propofol, and clonidine have all been used in this setting. More recently, the use of dexmedetomidine, a selective α ₂ -agonist with sedative, analgesic, amnestic, and antisialagogue properties, has been reported. A key advantage of dexmedetomidine is that it maintains spontaneous respiration with minimal respiratory depression. Patients being sedated with dexmedetomidine are generally easy to arouse. However, this advantage, along with that of maintaining spontaneous respiration, may not occur when very large doses are given.

Doyle described the successful use of the GlideScope in four cases of awake endotracheal intubation. The potential advantages are as follows: first, the view is generally excellent. Second, the method is less affected by the presence of secretions or blood as compared with the use of fiberoptic intubation. Third, no special restrictions exist on the type of ETT that can be placed when using the GlideScope, but this is not the case for fiberoptic methods. Fourth, the GlideScope is much more rugged than a fiberoptic bronchoscope and is far less likely to be damaged with use. Advancing the ETT into the trachea over the fiberoptic bronchoscope often fails as a result of ETT impingement on the arytenoid cartilages; this is generally not a problem with the GlideScope.

In the end, however, the use of awake fiberoptic intubation in the setting of the patient with airway disease remains steadfastly popular because it is gentle to the airway, is generally well tolerated, and does not require the application of force to obtain glottic exposure.

Special mention needs to be made of the necessity of being fully prepared for dire ENT airway emergencies because these patients may require immediate surgical intervention. In addition to a conventional difficult airway cart, practitioners may wish to maintain a special ENT airway cart with equipment such as that listed in Box 70.1 . In addition to these items and unlisted items favored by individual practitioners, ENT surgeons want ready access to an emergency tracheotomy tray, as well as to some form of suspension laryngoscope or rigid bronchoscope. Special attention to the maintenance and cleaning of fiberoptic bronchoscopes is also important, given that they must always be easily accessible and reliable when needed. In the case of electronic fiberscopes incorporating a video display, it is particularly important to establish that illumination settings and white balancing have been correctly set before use.

Airway Disorders in Otolaryngology

Otolaryngologic airway disorders can sometimes present the clinician with tremendous anesthetic and airway challenges. In many such cases, awake endotracheal intubation (e.g., by fiberoptic methods) is the method of choice. When awake intubation is impractical (e.g., overwhelming tumor invasion of the airway, inadequate equipment, limited experience), tracheostomy using local anesthesia (with minimal sedation, or no sedation in extreme cases) is sometimes preferred. In such cases, complete airway obstruction is the outcome most feared; this can occur when anesthetic drugs or neuromuscular blocking drugs decrease the tone of the airway musculature, thereby unfavorably changing the airway architecture.

Many ENT pathologic conditions can make airway management difficult. Airway infections can include upper airway abscesses, retropharyngeal abscesses, quinsy, Ludwig angina, and epiglottitis (supraglottitis). Airway tumors may be present as oral or tongue malignancies, as glottic, supraglottic, and infraglottic tumors, or as anterior mediastinal masses. Other pathologic conditions may also complicate airway management, such as congenital malformations (Pierre-Robin sequence, Goldenhar syndrome), periglottic edema (e.g., following rigid bronchoscopy), recurrent laryngeal nerve injury (e.g., following thyroid surgery), maxillofacial trauma, or OSA. Some of the more important of these conditions are discussed in the following paragraphs.

Airway Tumors, Polyps, and Granulomas

Airway tumors can be benign or malignant ( Figs. 70.5-70.7 ), but regardless of their pathologic characteristics, airway obstruction is always a potential concern. Discussion with the surgical team concerning the size and location of the tumor, along with a review of any video-recorded nasopharyngeal video examinations, will help determine whether awake endotracheal intubation is needed. Polyps may also be found throughout the airway and can lead to partial or complete airway obstruction. Vocal cord polyps, cysts, and granulomas may result from traumatic intubation, vocal cord irritation from ETT movement, or other causes, especially in women. Vocal cord cancer can also occur. The potential also exists for exacerbation of asthma in patients with nasal polyps who receive aspirin, ketorolac (Toradol), and other nonsteroidal antiinflammatory drugs (NSAIDs) (the Samter triad).

Anesthesia for Panendoscopy

Panendoscopy, sometimes known as triple endoscopy, involves three diagnostic components: laryngoscopy, bronchoscopy, and esophagoscopy. Such procedures and others involving the larynx, pharynx, or trachea often require specialized ENT laryngoscopes, frequently in conjunction with a small-diameter ETT or a tube specifically designed for laser surgery. Panendoscopy is used in patients with head and neck cancer to search for vocal cord lesions, obtain tissue biopsies, monitor for tumor recurrence, and so on. In such cases, one should consider the following specific issues in discussion with the surgical team: what is the anticipated pathologic process, and how is it expected to affect intubation or ventilation? (In some cases the patient’s disease may not allow the use of an ETT, so that jet ventilation or a rigid bronchoscope is needed.) What is the plan for airway management, and how does it affect the delivery of anesthesia? How does the presence of coexisting disease (e.g., coronary artery disease, chronic obstructive pulmonary disease, gastroesophageal reflux disease) affect management? What specialized equipment may be needed? (For example, when airway obstruction is present, the surgeon may employ dilatational balloons, lasers, or a microdébrider to open up the airway.)

Five airway options for panendoscopy exist: (1) use of an ETT, typically a narrow-bore MLT that provides the surgeon with a superior glottic view; (2) jet ventilation in conjunction with a rigid ENT laryngoscope, without the use of an ETT; (3) hybrid methods, such as the intermittent use of an SGA or an MLT tube in conjunction with a rigid laryngoscope, jet ventilation, or intermittent apnea; (4) tracheostomy using local anesthesia before inducing general anesthesia; and (5) elective placement of a specially designed transtracheal jet ventilation cannula (e.g., Ravussin jet ventilation catheter before induction ). The last two options are only occasionally used for patients with a suspected difficult airway; awake tracheal intubation is the most common approach in patients with a difficult airway. Moreover, when jet ventilation is used, total intravenous anesthesia (TIVA), for example with infusions of propofol and remifentanil, is needed. Finally, when panendoscopy is combined with laser surgery, a laser-safe ETT is often used.

Panendoscopy is generally done while the patient is under general anesthesia with the patient’s neck flexed and the head extended, usually employing a shoulder roll and a head ring (Jackson position). Typically, an anterior commissure laryngoscope is used and fixed into position by suspension ( Fig. 70.8 ). This technique allows the surgeon’s hands to be free and the operating microscope to be used. Other specialized ENT surgical laryngoscopes that are commonly used, often in conjunction with a microscope for laryngeal microsurgery, include the Dedo laryngoscope (Elmed, Addison, IL) and the Universal Modular Glottiscope (Endocraft, Providence, RI). Here, once the laryngoscope is correctly configured (“suspended”), the surgeon brings the operating microscope into the field and uses a variety of microlaryngeal instruments to treat the patient.

A variety of anesthetic techniques can be used for panendoscopy procedures. The most common approach is to perform the procedure while the patient is under general anesthesia with muscle relaxation in conjunction with an MLT-type tracheal tube ( Fig. 70.9 ). This technique is familiar to anesthesiologists, provides both airway protection and control of ventilation, allows for reliable capnographic carbon dioxide (CO ₂ ) measurements, and allows for the use of volatile anesthetics without operating room pollution. Disadvantages of the technique include higher than usual ventilation pressures as a consequence of the tube’s narrow diameter, somewhat hindered surgical access, and concerns for tube ignition when a laser is in use.

Because a tracheal tube may impair access to some glottic structures, however, some cases are performed using intermittent apnea during general anesthesia and administration of neuromuscular blocking drugs. Disadvantages of this technique include the need for a TIVA technique, the need for repeated intubation-extubation cycles (potentially producing glottic trauma), fragmentation of the surgical work into brief apneic segments, and the repeated interruption of ventilation and oxygenation.

Next, panendoscopy is often performed using supraglottic jet ventilation. This technique requires TIVA and entails some special issues because it involves the delivery of high-pressure oxygen pulses (typically 20-50 psi in adults, frequently delivered 1 second on/3 seconds off), usually through an adapter that attaches to the surgical laryngoscope. Additionally, subglottic methods (e.g., using a Hunsaker catheter ) and transtracheal methods of jet ventilation have been described. Each pulse of oxygen entrains room air, thus increasing the gas volume delivered and diluting the oxygen concentration (Venturi effect). Disadvantages of jet ventilation include the need for TIVA, the potential for barotrauma (remember that a pressure of 50 psi is equivalent to 3515 cm H ₂ O), an inability to measure either end-tidal CO ₂ (ETCO ₂ ) or tidal volume easily, and the fact that the technique is often suboptimal in obese individuals. Finally, a variant of jet ventilation known as high-frequency jet ventilation is sometimes used in these cases, often in conjunction with a special ventilator, an intratracheal catheter, and transcutaneous CO ₂ monitoring.