Chapter 34 Airway Management in the Intensive Care Unit*
The decision to instrument the airway of a patient is one of the most crucial taken; this approach to airway management, although often required in an emergency situation, requires considerable skill, experience, and knowledge of the different types of procedures available. The main reasons to instrument the airway are (1) failure of oxygenation, (2) failure of ventilation, and (3) protection of the airways.
Patients with a variety of medical and surgical diseases may require ventilatory assistance or improved airway control. Such patients include those with primary respiratory failure or with respiratory insufficiency secondary to other pathologic conditions. Implementation of respiratory support may be undertaken semielectively or on an emergency basis.
Airway instrumentation should be performed only by a skilled physician who has assessed the patient thoroughly addressing the risks and benefits for that patient. A vital step in this assessment is prediction of the ease with which intubation is likely to be possible, with identification of an appropriate alternative approach to use in case difficulties arise. An important point to remember is that patients die not because of a failure to intubate but as a result of failure to oxygenate; therefore, recurrent failed attempts to gain airway control should be avoided. Problems with ventilation can quickly lead to severe hypoxia, brain damage, or death.
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.
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).
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.
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.
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 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).
Risk Factors for Aspiration at Time of Intubation
|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
|0.3 M sodium citrate, 10 mL
|Neutralizes gastric pH but increases volume
Very effective at increasing gastric pH if given within 30 minutes
|Metoclopramide 10 mg
|Reduces gastric volume
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.
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.)