A 50-year-old singer presents for laser laryngoscopy. She has vocal fold polyps but otherwise is in good general health.
Is postoperative voice quality worthy of consideration by the anesthesia care team?
The anesthesia care team generally focuses on major life-threatening issues. Preoperative and postoperative hoarseness is a secondary concern. However, in the minds of patients who use their voices professionally, voice problems assume great importance. Phonosurgery is dedicated to restoring voice quality. Singers, actors, teachers, clergy, lawyers, politicians, and many others use their voices professionally. These patients strive for the best quality sounds possible. Singers in particular are anxious about laryngeal instrumentation, especially tracheal intubation. They are acutely aware of instances in which patients could not sing after either brief or prolonged intubation. Intubation injuries to vocal folds are usually due to anatomic disruptions or neuromotor injury. Examples of anatomic disruptions include vocal fold tears, intubation granuloma, arytenoid dislocation, and vocal fold edema. Prolonged intubation can be complicated by laryngeal stenosis, intubation grooves, or cricoarytenoid arthrodesis and granulomas. Neuromotor injuries include vocal fold paralysis or paresis secondary to recurrent laryngeal nerve compression from a high-riding endotracheal tube (ETT) cuff. Postintubation vocal fold paralysis is uncommon given the numbers of procedures performed under general anesthesia.
Some patients whose voices are unintelligible desire to restore speech for communication. For these patients, a hoarse or soft voice is better than no voice at all. Consequently, anesthesia-related voice complications that prevent them from speaking can have substantial consequences and are worthy of our attention.
What criteria are used to evaluate the airway?
Anesthesia societies in multiple countries recommend airway evaluation focusing on history and physical examination of surface landmarks. However, these recommendations ignore many sources of airway problems. The location and size of pathologic airway lesions can have significant effects on airway management. For esophageal pathologies, such as obstructing lesions, and gastrointestinal bleeding, the potential for aspiration should be explored. Inspiratory stridor suggests airway stenosis approximately 4 mm in diameter. However, the absence of stridor does not always indicate a normal-size airway, and stridor may be absent despite a very stenosed airway. Exhausted patients may not generate enough airflow to produce stridor, even in the face of significant stenosis. Voice changes such as hoarseness are nonspecific and frequently result from small, nonobstructive lesions or potentially from mediastinal lesions. Dysphagia suggests the possibility of supraglottic obstruction. Inability to lie flat, the need to sit upright, and frequent position changes to breathe are symptoms of severe airway obstruction.
Supraglottic and glottic masses are evaluated by nasopharyngoscopy in an awake, spontaneously breathing patient. Subglottic and tracheal problems are investigated with chest x-rays, computed tomography, or magnetic resonance imaging. These problems often manifest with inspiratory and expiratory stridor. Ideally, airway imaging should be reviewed and discussed with the surgeon. Previous anesthesia records could reveal prior problems with mask ventilation, laryngoscopy, bleeding, or extubation.
Explain the special anesthesia requirements for laryngeal microsurgery.
During laryngeal microsurgery procedures, surgeons and anesthesiologists occupy the same space at the same time. They must share the airway. The mouth and pharynx provide relatively little room for rigid suspension laryngoscopes and other tools, surgical visualization, and surgical manipulation. Millimeters of space can determine success or failure. Anesthesia equipment must take up as little room as possible. A small ETT or jet ventilation is generally used.
Airway surgery involves profound stimulation, requiring deep anesthesia for relatively brief periods. At the conclusion of surgery, stimulation quickly decreases to almost nothing, while patients remain deeply anesthetized. The goals for emergence are rapid awakening without coughing or bucking. Coughing or bucking abrades laryngeal incisions as vocal folds are forced against indwelling ETTs or the adjacent vocal fold. Coughing and bucking also can result in dislodgment of sutures and hemorrhage. Many patients are placed on voice rest postoperatively to prevent incision trauma that can impair healing. An opioid-based anesthetic with short-acting agents is desirable. An opioid-based anesthetic provides laryngeal sensory depression, allowing for smooth emergence.
Airway surgery is associated with the highest risk for postextubation airway compromise. It is of paramount importance to confirm adequate return of strength before extubation. It is the author’s preference to extubate awake patients as opposed to deeply anesthetized or heavily sedated patients. Strong muscle tone is required for airway dilator muscles to maintain upper airway patency. Conscious efforts to maintain an open airway contribute to successful extubation.
Describe an anesthetic for laryngeal microsurgery.
Phonomicrosurgery usually requires general anesthesia. Surgical access to the airway and aerodigestive tracts is improved by using small ETTs and adequate muscle relaxation. In the absence of muscle relaxation, deep planes of anesthesia are required. Suspension laryngoscopy is highly stimulating and tends to produce hypertension and tachycardia. Sufficient anesthetic depth and agents that effectively blunt sympathetic stimulation, such as remifentanil or β-adrenergic blockers, or both, are commonly used. Most of these procedures are of short duration, so judicious use of muscle relaxants and short-acting anesthetic agents is helpful. The operating room table is generally turned 90 or 180 degrees from its usual position. Respiratory circuits and cables need to be sufficiently long to extend the additional distance. Laser surgery is associated with its own special risks and is discussed later.
Mobile supraglottic lesions can obstruct gas flow through the larynx during positive pressure ventilation and obscure the glottis during laryngoscopy. Classically, patients with epiglottitis receive general anesthesia followed by laryngoscopy and intubation. Nevertheless, some supraglottic lesions may indicate the need for awake intubation.
Laryngeal lesions, such as large vocal cord polyps and papillomas, have the potential to create partial airway obstruction after induction of general anesthesia. They rarely result in total airway obstruction but can make mask (or other supraglottic airway) ventilation difficult. Contrary to classic teaching, obstruction is frequently worse in anesthetized spontaneously breathing patients than in anesthetized patients receiving positive pressure ventilation by facemask. Spontaneous ventilation is negative pressure ventilation. As the diaphragm and intercostal muscles contract, intrathoracic pressure is reduced. Reduced intrathoracic pressure falls below barometric pressure and is frequently referred to as negative pressure. Negative pressure is transmitted to the upper airway, where it tends to draw pharyngeal tissues into the airway. It is as if soft tissues are imploding into the upper airway. Pharyngeal dilator muscles normally work to maintain airway patency, but general anesthesia reduces muscle tone, allowing soft tissues to collapse inward. Positive pressure ventilation tends to stent the airway open, and consequently it is more effective in these cases. If spontaneous ventilation is maintained, assisted ventilation with positive pressure and oral or nasopharyngeal airways could be beneficial.
Spontaneous ventilation is useful to evaluate airway dynamics. Tracheomalacia is a prime example. In this case, inhalation induction is performed with sevoflurane and 100% oxygen. When a sufficient depth of anesthesia is achieved, laryngoscopy to view the trachea during inspiration and expiration can proceed.
Subglottic lesions do not inhibit laryngeal visualization but can prevent advancing an ETT beyond the larynx and into the trachea. If subglottic lesions are present, a variety of small ETTs and a jet ventilation system should be available. Small-diameter ETTs are required to allow for optimal surgical visualization and manipulation. For adult patients, 5.5 mm internal diameter (ID) ETTs generally satisfy this requirement and allow for adequate gas exchange. Controversy exists over the use of such small ETTs in large adults. Adequate minute ventilation delivered through small ETTs is accompanied by high readings on inspiratory pressure monitors. This is generally of little clinical importance because small ETTs act as resistors. There is a substantial decrease in pressure across a small ETT. Actual intratracheal pressures approximate pressures seen with larger ETTs. Consequently, the risk of barotrauma is not substantially greater using small ETTs than it is with large ones. A common technique to reduce inspiratory pressures is to adjust the inspiratory-to-expiratory (I:E) ratio from 1:2 to 1:1; this provides more time for inspiration, reducing the inspiratory pressure required to achieve adequate tidal volumes. Alternative modes of ventilation, such as pressure-controlled volume guaranteed, are also applicable.
For nonobstructing airway lesions, standard techniques of induction, maintenance, and ventilation work well. It is common practice to administer topical local anesthetic to the larynx and trachea during laryngoscopy. This practice is intended to reduce postoperative coughing and laryngospasm. Also, in the absence of muscle relaxants, anesthetized vocal folds help to provide vocal cord immobility. Lidocaine 2% or 4% solutions are commonly used for laryngotracheal anesthesia.
Vocal fold immobility is crucial for laryngeal surgery. Immobility is frequently achieved with muscle relaxants, but alternatives exist. For most short cases, reduced doses of commonly available intermediate-acting nondepolarizing neuromuscular blockers are appropriate. Loading doses of muscle relaxants should be avoided. Neuromuscular monitoring is required to determine the need for antagonism of the motor block and to determine sufficient return of strength for tracheal extubation. Airway surgery is associated with a relatively high risk of postextubation respiratory distress. Adequate muscle strength can reduce this risk.
An alternative to muscle relaxants is a deep plane of anesthesia; this is typically accomplished with total intravenous anesthesia using high-dose remifentanil (e.g., >0.2 μg/kg/min) or balanced anesthesia with remifentanil and volatile anesthetics. Relatively high doses of remifentanil render vocal cord movement unlikely. Avoiding muscle relaxants precludes anaphylaxis and residual neuromuscular blockade secondary to their use. High-dose opioids dampen the sympathetic response to laryngoscopy and intubation; however, they predispose to vocal cord adduction, which can impair mask ventilation and predispose to vocal cord trauma during intubation.
Anesthesia emergence can be accompanied by coughing and straining, both of which are potentially harmful after upper airway surgery. Forceful vocal cord adduction with or without an ETT in place exacerbates surgical tissue damage. The result is impaired healing, with vocal cord scarring and permanent adverse voice changes. Consequently, laryngeal topical anesthesia during airway manipulation and emergence from anesthesia and adequate opioid plasma levels are employed. Remifentanil offers intense analgesia and short duration of action, making it an excellent opioid choice. Alternatively, deep extubation can be considered to help reduce coughing on emergence. However, deep extubation risks aspiration of blood and debris that frequently accompanies airway surgery. High-dose opioids allow patients to awaken comfortably with the ETT in place, after which extubation can occur when they are able to protect their own airways ( Box 44-1 ).