Indications for Airway Support

The most common indication for ventilatory support in intensive care is acute respiratory failure, resulting in hypoxia, hypercapnia, or increased work of breathing, necessitating the need for positive-pressure ventilation. This can be provided as noninvasive ventilation (NIV) or as invasive ventilation requiring intubation. Intubation also may be indicated with loss of airway reflexes associated with a reduced level of consciousness, meaning that the patient is unable to protect their airway. Airway protection may be needed in cases of airway soiling or excessive secretion with inadequate cough. The neurosurgical patient managed in the ICU may require ventilation to regulate PaCO₂ for control of intracranial pressure. Endotracheal intubation also may be needed when swelling or trauma to the upper respiratory tract results in impending airway loss.

Noninvasive Ventilation

Patients with respiratory failure and preserved airway reflexes may benefit from NIV. The rationale for this application, most commonly seen in acute exacerbations of chronic obstructive pulmonary disease (COPD), is that NIV may reduce the work of breathing and help to correct hypercapnic or hypoxic respiratory failure. NIV is contraindicated, however, with cardiovascular or respiratory instability, compromised ability to handle secretions, aspiration risk, or inability to tolerate a tight-fitting face mask (see Chapter 33 on NIV).

Airway Assessment

Before instrumentation of the patient’s airway, a thorough assessment should be performed to ascertain the likelihood of difficulty in achieving airway control. Several specific aspects of this assessment are considered next.

Predictors of Difficult Mask Ventilation

Difficult mask ventilation is encountered in 8% of patients. Patients at risk for such difficulty include those with preexisting partial airway obstruction, snorers, those with facial asymmetry, the obese, persons with Mallampati class IV airway anatomy (complete lack of epiglottis visualization), and the edentulous. Management of patients with facial hair, which often hides a receding mandible and in itself makes a seal for mask ventilation difficult, can present significant problems.

Predictors of Difficult Intubation

Difficult intubation is common in the ICU population, with frequency of reported difficulty between 6.6% and 22%. A history of airway problems should be sought—for example, snoring, sleep apnea, congenital diseases (such as Down or Pierre-Robin syndrome), and previous anesthetic problems.

Examination of the patient should determine the following: ability to protrude the mandible, range of neck movement, atlantooccipital flexion and extension, interincisor distance (less than 3 cm indicates a high likelihood of difficulty), and modified Mallampati test (Figure 34-1). Other predictors of difficult intubation include thyromental distance of less than 7 cm (Patil’s test) and obesity. Further investigations when indicated could include the view of the larynx obtained at nasal endoscopy, which may predict the view at laryngoscopy; chest radiographs, which may show tracheal deviation or mediastinal masses; and CT scans, which may be useful when abnormal anatomy is suspected—for example, in association with tracheal stenosis.

Figure 34-1 Mallampati test to classify view of the pharynx. For this test, the patient is asked to protrude the tongue fully while opening the mouth maximally, with the head in the neutral position. Class I: The pharyngeal pillars, soft palate, and uvula are visible. Class II: Only the soft palate and uvula are visible. Class III: Only the soft palate is seen. Class IV: Only the hard palate is seen. Mallampati class correlates with Cormack and Lehane grade for the view at laryngoscopy (see Figure 34-5). Increasing class suggests more difficult laryngoscopy.

Aspiration Risk

Aspiration of gastric contents can cause significant morbidity and mortality. Evidence suggests that reducing gastric volume and increasing pH of gastric contents will limit the risk of disorders associated with aspiration. Acid aspiration may lead to a chemical pneumonitis, but aspiration of food particles can result in physical obstruction of the bronchial tree with secondary bacterial pneumonia (Box 34-1 and Table 34-1).

Box 34-1

Risk Factors for Aspiration at Time of Intubation

Instrumentation before postprandial interval of less than 6 hours

Obesity

Pregnancy

Hiatus hernia

Intraabdominal pathology

Vomiting

Symptomatic reflux

Table 34-1 Drugs to Reduce Aspiration Risk

Drug Class	Specific Agent	Mechanism of Action
Histamine H₂ receptor antagonists	Ranitidine 50 mg IV	Increases pH and decreases gastric volume
Proton pump inhibitors	Omeprazole 40 mg IV	Irreversibly binds H⁺/K⁺-ATPase; increases pH and decreases gastric volume
Nonparticulate antacids	0.3 M sodium citrate, 10 mL	Neutralizes gastric pH but increases volume Very effective at increasing gastric pH if given within 30 minutes
Prokinetics	Metoclopramide 10 mg	Reduces gastric volume

Basic Airway Maneuvers and Airway Adjuncts

Patients with complete or partial airway obstruction may benefit from basic airway maneuvers to open the airway. Depending on the cause of airway compromise, suctioning may be needed to remove foreign bodies. Neck flexion with extension at the atlantooccipital joint and a chin lift can be used when upper airway tone is reduced; a jaw thrust should be used with in-line stabilization when cervical spine injury is suspected. In patients with a reduced level of consciousness, insertion of an appropriately sized oropharyngeal or nasopharyngeal airway may be helpful.

Endotracheal Intubation with Muscle Relaxation

Positioning

Putting the patient in the optimal position is the first and most important step. Appropriate positioning allows good access to the airway and allows efficient preoxygenation. Other advantages include improvement of the laryngoscopic view and, with the head held slightly up, a reduced risk for aspiration of gastric contents. The “head-up” position also increases functional residual capacity by allowing better diaphragmatic excursion, thereby increasing oxygen reserves. The patient should be positioned with the neck flexed on a pillow, but with the head extended, so long as cervical spine injury is not suspected. Positioning is of particular importance in the obese patient (Figure 34-2).

Figure 34-2 Positioning the obese patient. Correct positioning is important to optimize the view during laryngoscopy. Flexion of the lower cervical spine brings the trachea in line with the pharynx, and extension at the atlantooccipital joint aligns the trachea with the oral cavity. With the obese patient in the supine position, neck movement and access with a laryngoscope are hindered by fat. When the patient is repositioned with the shoulders elevated and the occiput further elevated so that the head assumes a “sniffing” position, access to the airway is facilitated.

(From Wiener-Kronish JP, Shimabukuro DW: Airway management. In Albert RK, Spiro SG, Jett JR, editors: Clinical respiratory medicine, ed 3, Philadelphia, 2008, Mosby.)