Anesthesia for laryngeal operations

Published on 07/02/2015 by admin

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Anesthesia for laryngeal operations

Gurinder M.S. Vasdev, MD, MBBS and Barry A. Harrison, MD

In operations involving the larynx, both the surgeon and the anesthesiologist must share the patient’s airway, making an understanding of the operative and anesthesia requirements and ongoing communication among team members essential. Indications for laryngeal operations include congenital (Box 155-1) and acquired conditions. The main acquired conditions include trauma, inflammatory conditions, and tumor (benign and malignant). Laryngeal signs and symptoms vary from a sore throat and hoarseness to difficulty in breathing, stridor, and, if severe, complete upper airway obstruction. The main types of laryngeal operations that necessitate anesthesia, including management of the airway, are direct laryngoscopy, thyroplasty, laryngectomy, and importantly, trauma to the larynx.

Airway anatomy and physiology

The human larynx has three basic functions: inspiration, tracheobronchial protection, and phonation. These tasks are achieved through a complex system of neuronal innervation to intrinsic and extrinsic laryngeal musculature suspended on cartilaginous structures. The vagus nerve (cranial nerve X), via the superior and recurrent laryngeal nerve, is responsible for the sensory and motor innervation of the larynx. The internal branch of the superior laryngeal nerve provides ipsilateral sensation to the supraglottic (i.e., above the true vocal folds) larynx. Below the vocal cords, ipsilateral sensation is supplied by the recurrent laryngeal nerve. The posterior half of the vocal cords has the highest density of touch receptors. This is important to remember during fiberoptic intubation when regional or topical anesthesia is used. Stimulation of epiglottic water-sensitive chemoreceptors causes slowed respiration with increased tidal volume, resulting in increased laryngeal airflow. This centrally mediated response appears to be more active in children and is a mechanism by which humidification improves breathing during partial airway obstruction (i.e., slow, large-tidal-volume breathing decreases turbulent airflow).

The recurrent laryngeal nerve provides the motor supply to all intrinsic laryngeal muscles except the cricothyroid muscle. The cricothyroid muscle receives motor innervation from the external branch of the superior laryngeal nerve. The actions of each muscle are summarized in Figure 155-1. There is little chance of effective reinnervation with good laryngeal function when trauma to these nerves occurs.

Figure 155-1 The intrinsic muscles of the larynx. (Netter illustration from www.netterimages.com. © Elsevier Inc. All rights reserved.)

Phonation is produced by fundamental tone formation in the larynx. This is modified by the resonating chambers of the upper airway. Frequency is determined by isotonic contraction of the cricothyroid muscle. Pitch is determined by changes in the length of the cords and subglottic pressure.

This knowledge is applied in thyroid and parathyroid operations, during which recurrent laryngeal nerve injury may occur. To minimize the possibility of nerve injury, surgeons monitor recurrent laryngeal nerve function by stimulating this nerve via a tracheal tube positioned at the level of the larynx, with the stimulation occurring at the level of the larynx and the recording electrodes positioned at the level of the vocal cords.

Direct laryngoscopy

Direct laryngoscopy is used for supraglottic, glottic, subglottic, and tracheal examinations for diagnostic, therapeutic, or both diagnostic and therapeutic purposes. Because preexisting cardiac disease accounts for 1.5% to 4% of perioperative deaths in this patient population, preoperative cardiac assessment is important. Preoperative airway assessment is equally important and includes a physical examination, either direct or indirect laryngoscopy, computed tomography, and magnetic resonance imaging. If airway patency is questionable, then awake fiberoptic intubation, tracheotomy, or tracheostomy should be performed under local anesthesia. Premedication with an antisialagogue is beneficial. In surgical procedures requiring general anesthesia, induction can be achieved with either spontaneous ventilation (using a nonirritating inhalation anesthetic) or intravenously administered medications. Topical application of local anesthetic on the vocal cords and adjacent mucosa can decrease the requirements for inhalational anesthesia. Oxygenation is maintained with the use of insufflation in a spontaneously breathing patient with or without the use of a tracheal tube.

Regardless of the technique used, dental injury can occur. Patients with difficult airways are at particular risk for incurring a dental injury. Otorhinolaryngologic surgeons often use dental guards in patients to reduce the risk of injury during direct laryngoscopy. Postsurgical hemoptysis, obstruction, laryngeal edema, and laryngospasm are major risks associated with direct laryngoscopy. As modern technology evolves, direct laryngoscopy may be replaced by indirect methods.

Without a tracheal tube

Apneic oxygenation

During apneic oxygenation, patients are hyperventilated with 100% O₂ and an inhalation anesthetic agent. The surgeon is then allowed airway access in 3-min to 5-min epochs or until desaturation occurs. CO₂ monitoring is not possible with this technique; accordingly, hypercapnia is a potential problem.

Jet ventilation

In jet ventilation, air is entrained by the Venturi effect when a 30-psi to 50-psi blast from the jet ventilator insufflates O₂ into the airway. A properly placed jet allows visualization of chest wall movement. During jet ventilation, inhalation anesthesia is not possible; intravenously administered anesthesia is best suited for this oxygenation technique.

With a tracheal tube

Microlaryngeal tubes

Microlaryngeal tubes are tracheal tubes with a 3.5-mm to 4-mm external diameter that require stylet-guided placement. General anesthesia should be maintained with short-acting medications because emergence can be challenging. If a laser is being used, a tracheal tube that is laser compatible must be used.

Thyroplasty

Vocal cord operations requiring injection of Teflon, gelatin, botulinum neurotoxin, or steroid can be performed with conscious sedation but may require general anesthesia. The typical patient undergoing a thyroplasty has paralysis of a vocal cord secondary to injury to the recurrent laryngeal nerve. The use of a supraglottic airway is important for the patient who has previously had a thyroplasty and who now requires a general anesthetic.

Laryngectomy

Laryngeal carcinoma accounts for 2% to 3% of all malignancies. Tobacco or alcohol use, radiotherapy, and herpes simplex infection have been implicated as risk factors for the development of laryngeal carcinoma. Patients are predominantly men over the age of 50 years. Laryngeal carcinoma occurs in supraglottic (30%), glottic (60%), and subglottic (10%) forms.

Careful preoperative patient assessment is vital because these patients often have significant comorbid disease (e.g., chronic obstructive pulmonary disease, coronary artery disease, congestive heart failure, hypertension, nicotine dependence, and alcohol abuse). Liver function should be evaluated in patients with a significant history of alcohol intake.

The airway is often secured using awake techniques with conscious sedation (e.g., fiberoptic intubation or tracheotomy). The type of anesthesia (i.e., awake vs. general) is determined by airway anatomy, severity of comorbid diseases, patient preference, and health care team preference. Continuous monitoring of arterial pressure via an indwelling arterial cannula is helpful, particularly when the neck dissection involves the area around the carotid sinus. Additionally, an arterial catheter provides access for obtaining blood for laboratory studies (e.g., obtaining serial hemoglobin concentrations), which is essential during surgical procedures associated with large blood loss (e.g., total laryngectomy with neck dissection). If the use of a central venous catheter is indicated, the catheter can be placed via the subclavian route or a long line can be inserted from the antecubital space or via the femoral vein. Potential perioperative complications include air embolism, hypertension, parathyroid and cranial nerve dysfunction, and facial edema. The use of a nasogastric tube is helpful in the postoperative period for both gastric drainage and postoperative feeding. Preliminary experience with transoral robotic surgery for head and neck cancer is encouraging, suggesting that this modality will be used more frequently in the future.

Laryngeal and tracheal trauma

Laryngeal or tracheal trauma is seen in approximately 1 in 43,000 emergency department admissions. Clinical signs include hoarseness, tenderness, subcutaneous emphysema, respiratory distress (e.g., stridor), dysphagia, and hemoptysis. The best outcomes are observed when an otolaryngologist is involved in managing the patient’s airway and any treatment is performed in the operating room. If the patient’s airway is stable, oral intubation under general anesthesia, with either rapid sequence or inhaled induction, may be used. If the patient’s airway is unstable, if the laryngeal mucosa is disrupted, or if the patient has a laryngoskeletal fracture (confirmed with computed tomography), awake fiberoptic intubation or awake tracheotomy under local anesthesia should be performed. Inhaled induction of anesthesia followed by orotracheal intubation may be necessary in confused or uncooperative patients, even in the presence of a risk for aspiration.

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