1 List several indications for endotracheal intubation

General anesthesia but there are alternatives to endotracheal intubation

Positive-pressure ventilation

Protecting the respiratory tract from aspiration of gastric contents

Surgical procedures in which the anesthesiologist cannot easily control the airway (e.g., prone, sitting, or lateral decubitus procedures)

Situations in which neuromuscular paralysis has been instituted

Surgical procedures within the chest, abdomen, or cranium

When intracranial hypertension must be treated

Protecting a healthy lung from a diseased lung to ensure its continued performance (e.g., hemoptysis, empyema, pulmonary abscess)

Severe pulmonary and multisystem injury associated with respiratory failure (e.g., severe sepsis, airway obstruction, hypoxemia, and hypercarbia of various etiologies)

2 Review objective measures suggesting the need to perform endotracheal intubation

These objective measures are often used for patients in critical-care settings, not necessarily perioperatively. But they also are useful in determining which patients should not be extubated after surgery.

Respiratory rate >35 breaths/min

Vital capacity <5 ml/kg in adults and 10 ml/kg in children

Inability to generate a negative inspiratory force of 20 mm Hg

Arterial partial pressure of oxygen (PaO₂) <70 mm Hg on 40% oxygen

Alveolar-arterial (A-a) gradient >350 mm Hg on 100% O₂

Arterial partial pressure of carbon dioxide (PaCO₂) >55 mm Hg (except in chronic retainers)

Dead space (Vd/Vt) >0.6

3 What historical information might be useful in assessing a patient’s airway?

Patients should be questioned about adverse events related to previous airway management episodes. For instance, have they ever been informed by an anesthesiologist that they had an airway management problem (e.g., “difficult to ventilate, difficult to intubate”)? Have they had a tracheostomy or other surgery or radiation about the face and neck? Have they sustained significant burns to these areas? Do they have obstructive sleep apnea, snoring, or temporomandibular joint (TMJ) dysfunction? Review of prior anesthetic records is always helpful.

4 Describe the physical examination of the oral cavity

Examine the mouth and oral cavity, noting the extent and symmetry of opening (three fingerbreadths is optimal), the health of the teeth (loose, missing, or cracked teeth should be documented), and the presence of dental appliances. Prominent buck teeth may interfere with the use of a laryngoscope. The size of the tongue should be noted (large tongues rarely make airway management impossible, only more difficult), as should the arch of the palate (high-arched palates have been associated with difficulty in visualizing the larynx).

5 Review the Mallampati classification

The appearance of the posterior pharynx may predict difficulty in laryngoscopy and visualization of the larynx. It has been noted through meta-analysis that, when used alone, the Mallampati test has limited accuracy for predicting the difficult airway and thus it is clear that a comprehensive airway examination, not just a Mallampati classification, is necessary to identify patients who may be difficult to intubate. This classification also does not address the issue of ease of mask ventilation.

Mallampati has organized patients into classes I to IV based on the visualized structures (Figure 8-1). Visualization of fewer anatomic structures (particularly classes III and IV) is associated with difficult laryngeal exposure. With the patient sitting upright, mouth fully open, and tongue protruding, classification is based on visualization of the following structures:

Class I: Pharyngeal pillars, entire palate, and uvula are visible.

Class II: Pharyngeal pillars and soft palate are visible, with visualization of the uvula obstructed by the tongue.

Class III: Soft palate is visible, but pharyngeal pillars and uvula are not visualized.

Class IV: Only the hard palate is visible; the soft palate, pillars, and uvula are not visualized.

Figure 8-1 Mallampati classification of the oropharynx.

6 What is the next step after examination of the oral cavity?

After examination of the oral cavity is completed, attention is directed at the size of the mandible and quality of TMJ function. A short mandible (shorter than three fingerbreadths) as measured from the mental process to the prominence of the thyroid cartilage (thyromental distance) suggests difficulty in visualizing the larynx. Patients with TMJ dysfunction may have asymmetry or limitations in opening the mouth and popping or clicking. Manipulation of the jaw in preparation for laryngoscopy may worsen symptoms after surgery. Curiously some patients with TMJ dysfunction have greater difficulty opening the mouth after anesthetic induction and neuromuscular paralysis than when they are awake and cooperative.

7 Describe the examination of the neck

Evidence of prior surgeries (especially tracheostomy) or significant burns is noted. Does the patient have abnormal masses (e.g., hematoma, abscess, cellulitis or edema, lymphadenopathy, goiter, tumor, soft-tissue swelling) or tracheal deviation? A short or thick neck may prove problematic. A neck circumference of greater than 18 inches has been reported to be associated with difficult airways. Large breasts (e.g., a parturient) may make using the laryngoscope itself difficult, and short-handled laryngoscope handles have been developed with this in mind.

It is also important to have the patient demonstrate the range of motion of the head and neck. Preparation for laryngoscopy requires extension of the neck to facilitate visualization. Elderly patients and patients with cervical fusions may have limited motion. Furthermore, patients with cervical spine disease (disk disease or cervical instability, as in rheumatoid arthritis) may develop neurologic symptoms with motion of the neck. Radiologic views of the neck in flexion and extension may reveal cervical instability in such patients.

It is my experience that the preoperarative assessment of range of motion in patients with prior cervical spine surgery does not equate well with their mobility after anesthetized and paralyzed, suggesting that in this patient group wariness is the best policy and advanced airway techniques, as will be described, should be considered.

Particularly in patients with pathology of the head and neck such as laryngeal cancer, it is valuable to know the results of nasolaryngoscopy performed by otolaryngologists. (This is always the case in ear, nose, and throat surgery—never assume anything. Always work closely and preemptively with the surgeon to determine how the airway should be managed.) Finally, if history suggests dynamic airway obstruction (as in intrathoracic or extrathoracic masses), pulmonary function tests, including flow-volume loops, may alert the clinician to the potential for loss of airway once paralytic agents are administered.

8 Discuss the anatomy of the larynx

The larynx, located in adults at cervical levels 4 to 6, protects the entrance of the respiratory tract and allows phonation. It is composed of three unpaired cartilages (thyroid, cricoid, and epiglottis) and three paired cartilages (arytenoid, corniculate, and cuneiform). The thyroid cartilage is the largest and most prominent, forming the anterior and lateral walls. The cricoid cartilage is shaped like a signet ring, faces posteriorly, and is the only complete cartilaginous ring of the laryngotracheal tree. The cricothyroid membrane connects these structures anteriorly. The epiglottis extends superiorly into the hypopharynx and covers the entrance of the larynx during swallowing. The corniculate and cuneiform pairs of cartilages are relatively small and do not figure prominently in the laryngoscopic appearance of the larynx or in its function. The arytenoid cartilages articulate on the posterior aspect of the larynx and are the posterior attachments of the vocal ligaments (or vocal cords). Identification of the arytenoid cartilages may be important during laryngoscopy. In a patient with an anterior

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