Anesthesia for Laryngeal Surgery

Issues of Concern

Laryngeal Anatomy

The laryngeal structures are composed of a cartilaginous skeleton, musculature, as well as a mucosal lining. The larynx functions in phonation, airway maintenance and protection, and the generation of the Valsalva maneuver. The anatomical structures of the larynx include cartilage, vocal folds (or cords), muscles, and innervation.[2] Cancer or cancer treatment in the larynx or surrounding structures may result in anatomic changes that may cause airway management difficulties. The structures or spaces around the epiglottis and lateral to the vocal cords may decrease compliance, cause airway narrowing, or make endotracheal tube (ETT) passage difficult or impossible. Airway management in patients with laryngeal cancer varies based on the stage and location of the cancer. Patients with early laryngeal cancer usually have airways suitable for ETT passage, while those with more advanced cancer may have a narrowed airway lumen and decreased tissue compliance, proving ETT passage more difficult.[3]

Preanesthetic Assessment and Surgical Considerations

A medical history and focused physical examination should be performed, with a special focus on the airway and medical conditions associated with complications during or following the procedure. In addition, airway assessment, including a review of radiologic studies, should be performed with the identification of any possible difficulties and risk factors during anesthesia, as patients undergoing head and neck procedures are predisposed to airway difficulties. During laryngeal surgery, the surgeon and anesthesiologist share the airway. Thus, anesthesia management requires close coordination with the surgeon. A preoperative discussion of airway management device selection, intubation technique(s), ventilation strategy, neuromuscular blockade, fire risk, and table orientation should occur.[4]

Common Procedures

Phonosurgery includes procedures intended to treat voice disorders, including hoarseness and changes in laryngeal sound production.[5] This may require the patient to be conscious during the procedure to assess voice function. Procedures that require microlaryngoscopy, surgical innervation of the larynx, or soft tissue lesion excisions require general anesthesia, while those that do not require microsurgery may be performed with regional or topical anesthesia.[6] Pathology includes glottal lesions (such as papillomatosis), nodules, and polyps on the vocal folds (ie, from overuse).[7]

Laryngoplasty

Procedures may be performed to improve respiratory or voice function by enlarging the glottic opening or by bringing together the vocal folds. Laryngoplasty may be classified as injection or operative. Injection laryngoplasty is an endoscopic procedure for the treatment of voice disorders or glottic insufficiency. A bulking agent is injected to medialize the vocal folds, thereby improving sound quality. This procedure requires 15 to 20 minutes of operative time and, as a result, may be performed under local anesthesia, unless the surgical field must be immobilized or if patients are anxious about being awake. Operative laryngoscopy, or thyroplasty, may also be performed without sedation. Medialization may be performed for unilateral vocal cord paralysis, in which a permanent wedge is implanted to medialize the impaired vocal cord. This procedure takes 45 to 90 minutes, and moderate sedation can be used, as voice testing is often utilized during the operation. Mild postoperative throat discomfort is expected. As a result, opioids are avoided whenever possible for both injection and operative laryngoplasty. 

Laryngeal Cancer Surgery

Anesthetic planning for laryngeal surgery must provide intraoperative ventilation and oxygenation for the patient. The choice of ventilatory mode depends on the type of laryngeal disease, patient characteristics, and the length of the procedure.[8] Procedures expected to last longer than one hour should be secured with jet ventilation or mechanical-controlled ventilation (eg, ETT tube). Shorter procedures may be more amenable to apneic intermittent ventilation. Laryngeal cancer itself may impede airway management via mass effect, local tissue inflammation, edema following radiation or fibrosis, as well as scarring from prior surgery. Patients may also be anxious, malnourished, or hypovolemic before the surgical procedure. For the excision of a variety of vocal fold lesions, microlaryngeal surgery is performed using specialized laryngoscopes under general anesthesia and usually requires less than two hours of operative time.

Ventilation Technique

The anesthesiologist and surgeon should discuss a plan for intraoperative ventilation based on the surgery planned.[4] Total intravenous anesthesia may be used to obviate concerns regarding the presence of an open airway.[1] Continuous infusions of propofol or remifentanil can be utilized, with or without superior laryngeal nerve block. Maintaining spontaneous ventilation allows the surgeon uninterrupted and unobstructed surgical access for suspension micro laryngoscopy. Supplementation with mask ventilation, jet ventilation, or endotracheal ventilation may be necessary during periods of hypoventilation or desaturation.[9] High-flow nasal oxygenation (>15 L/min) via nasal cannula may be used for upper airway surgeries while maintaining spontaneous ventilation. This method of ventilation is associated with complications including hypoxemia, hypercapnia, and airway fire.[10]

Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) may be of clinical utility before securing a definitive airway in patients with reduced time to apnea (apneic window) and unfavorable pharyngeal anatomy.[11] Many patients undergoing laryngeal surgery have pathology or previous therapy that may make them difficult to intubate. The use of THRIVE has allowed for up to 17 minutes of apneic time without signs of carbon dioxide toxicity. The rate of carbon dioxide accumulation is 0.15 kPa/min with the use of THRIVE compared to 0.45 kPa.min in patients undergoing traditional apneic oxygenation or those with airway obstruction. Continuous positive airway pressure of 7 cm is believed to contribute, to splinting the upper airways and reduced shunting. Continuous insufflation facilitates carbon dioxide clearance through gaseous mixing and flushing of dead space.[11]

Endotracheal Intubation

A cuffed endotracheal tube secures the airway and prevents leakage of anesthetic gas or oxygen but may interfere with visualization and dissection of the laryngeal lesion. Special care must be taken to avoid injuring laryngeal lesions during intubation. The smallest endotracheal tube (ETT) capable of supporting ventilation should be used. In most cases, a 5 or 5.5 mm micro laryngeal tube is adequate, but special attention should be paid to air leaks using small diameter ETT. Laser-resistant ETTs are used for laryngeal laser surgery to reduce the risk of airway fire. Endotracheal tube material should be selected based on the type of laser used for the procedure. Laser-resistant tubes have a larger external diameter due to the resistant coating materials.

Intraoperative Laser Use

Most laryngeal surgery is performed with carbon dioxide (CO2) lasers. The most commonly used laser-resistant ETT, the Laser-Flex cuffed ETT, is CO2 and KTP laser-resistant and has two cuffs. The second cuff provides a backup seal in the event of damage to the proximal cuff. The cuff position should be rechecked after the patient is positioned for surgery, with special care as the laser-resistant ETTs have no depth markings. Laryngeal laser surgery is indicated to treat stenoses, recurrent respiratory papillomatosis, leukoplakia, malignant or benign laryngeal tumors, or polyploid degeneration (ie, Reinke edema).[12] Though their use is associated with a reduced fire risk, carbon dioxide lasers cannot be used for precise cutting without causing trauma to the delicate subepithelial vocal fold tissue.[7]

According to the American Society of Anesthesiologists Practice Advisory for the Prevention of Operating Room Fires, the ETT cuff should be filled with saline tinted with methylene blue to alert the clinician of an ETT cuff rupture during laser surgery.[13] The surgeon should alert the anesthesiologist in advance before laser activation; inspired oxygen concentration should be reduced to below 30% and nitrous oxide should be discontinued. It will take approximately 5 minutes to equilibrate, depending on fresh gas flow, circuit length, and starting oxygen concentration.[14]

The time to ignition of OR fires caused by carbon dioxide lasers can be reduced by replacing nitrogen with helium. Fire risk can be attributed to the pervasive use of incendiary operating tools (diathermy and lasers) and the oxygen-enriched environment.[15] Complications arising from laser use in the operating room include gas embolism, laser plume creation, retinal injury, operating room fire, and damage to vascular structures. Up to 32% of operating room fires are caused by lasers during laryngeal surgery.[15]

Subglottic (Transoral-Translaryngeal-Infraglottic Access) Jet Ventilation

Advances in jet ventilation tube design have facilitated safe anesthesia for laryngeal surgery.[16] High-frequency jet ventilation (HFJV) via a catheter placed in the cricothyroid membrane is useful for oxygenating patients undergoing microlaryngcopic and laser surgery. Whereas tracheal tubes may hide the posterior glottis and carry airway fire risk, HFJV helps limit both of these disadvantages. It may also be used post-procedurally to provide oxygenation as the patient recovers from anesthesia.[17] The cricothyroid membrane has no blood vessels and low bleeding risk. Transtracheal ventilation should be administered in the midline. Adverse events are mainly related to the puncture through the cricothyroid membrane, mechanical problems, and low saturation. Carbon dioxide retention may occur, especially in patients with pre-existing chronic obstructive pulmonary disease or obesity. Pneumomediastinum, subcutaneous emphysema, and pneumothorax are rare complications of HFJV.[17] Patients with a history of previous laryngeal surgeries or those undergoing longer operations may be at increased risk for complications following HFJV during endolaryngeal surgery.[18]

Clinical Significance

Laryngeal surgery presents its unique challenges for anesthesiologists, including coordination among the surgeon and other allied health providers. The airway must be shared between the anesthesiologist and the surgeon, for instance. The treatment of common laryngeal pathology limits neck mobility and increases tissue friability. A thorough history and physical must be performed to evaluate for changes to airway friability (eg, from radiation). The pathology itself (eg, vocal cord tumor) may provide challenges to airway management and often requires visual assessment preoperatively. Numerous ventilation options exist depending on the length and unique demands of the case and the patient. Additionally, the use of lasers during laryngeal surgery presents a significant fire risk, and this must be mitigated as much as possible.

Enhancing Healthcare Team Outcomes

Coordination between the anesthesiologist, anesthetic providers, and the otolaryngologist is paramount during preparation for laryngeal surgery. Intubation and ventilation should be discussed, as well as extubation.

Nursing, Allied Health, and Interprofessional Team Interventions

As laryngeal surgery is an aerosol-generating procedure, the use of PPE to prevent infection control is paramount. A previous investigation analyzing communication in the pediatric operating theater during airway surgery has shown detrimental effects on communication among OR staff as a result.[19] Communication aids are recommended, but no specific device, speech-to-text app, or software has been validated.

Nursing, Allied Health, and Interprofessional Team Monitoring

Communication among nursing, allied health, and interprofessional team members is important. Monitoring any barriers to communication, such as personal protective equipment, as well as planning for airway management and patient positioning is integral to effective anesthesia during laryngeal surgery. Communication and monitoring of fire risk during the preoperative time out and throughout the procedure is critical to a successful surgery.