Chapter 33: Airway Management

Although noninvasive ventilation is used increasingly, many mechanically ventilated patients are managed with an endotracheal tube or tracheostomy. Thus, an understanding of airway management is important for those providing mechanical ventilation.

There are four traditional indications for an artificial airway:

1. Provide ventilatory support.

2. Aid in the removal of secretions.

3. Bypass upper airway obstruction.

4. Prevent aspiration.

Each of these is a relative indication. For example, ventilatory support and airway clearance can be provided noninvasively. Massive aspiration can be minimized by use of an artificial airway, although microaspiration commonly occurs in the presence of a cuffed artificial airway.

Potential advantages of nasotracheal intubation include greater tolerance in the patient who is awake, easier oral hygiene, ease of intubation in the patient with cervical spine injury, and decreased likelihood of self-extubation. However, the disadvantages of nasal intubation outweigh these advantages. Because nasotracheal intubation requires a narrower and longer tube, it increases airway resistance, makes suctioning and bronchoscopy more difficult, and increases the likelihood of sinusitis and otitis media. Accordingly, oral intubation is usually recommended, and the oral route is used in most intubated patients.

A life-threatening complication of airway management is misplacement of the tube (Table 33-1). Although many patients who experience an unplanned extubation do not require reintubation, there is significant morbidity and mortality associated with the need for reintubation. Efforts to avoid unplanned extubation include securing the tube (around-the-head techniques are preferred), physical and chemical restraint when necessary, and vigilance of airway position when the patient or ventilator tubing is moved. The endotracheal tube can be misplaced into the esophagus or mainstem bronchus (usually the right). Although this usually occurs at the time of intubation, it can occur after intubation. The tip of the endotracheal tube can move several centimeters as the result of flexion and extension of the neck—flexion moves the endotracheal tube tip caudad and extension moves it cephalad.

As a landmark, the centimeter marking on the tube at the lip or nares should be recorded when proper tube position is determined and this landmark should be checked frequently. For the newly intubated patient, the oral endotracheal tube should generally be inserted 21 cm at the teeth for females and 23 cm for males. Tube position should be assessed frequently by auscultation and on a regular basis by chest X-ray. A thorough evaluation of endotracheal tube position should be performed immediately following intubation (Table 33-2).

The presence of the endotracheal tube is traumatic to the airway. The larynx and tracheal wall are particularly prone to injury, which may not be recognized until after extubation. Laryngeal injuries include edema, vocal cord paralysis, glottic stenosis, and granulation formation. Tracheal injuries include tracheal stenosis, tracheomalacia, and fistula formation to the esophagus or innominate artery. Tracheal injuries are usually related to compression of the tracheal mucosa by the endotracheal tube cuff. Tracheal wall injury can be ameliorated by avoidance of cuff overdistention, which is facilitated by cuff pressures of less than 30 cm H₂O. On the other hand, the risk of silent aspiration is increased with cuff pressures less than 20 cm H₂O. Thus, cuff pressures should be monitored at regular intervals and should be maintained in the range of 20 to 30 cm H₂O.

Cuff leaks occasionally occur. This can be due to cuff rupture, accidental severing of the pilot tube, or malfunction of the pilot balloon valve mechanism. Inability to maintain cuff inflation usually results in failure to adequately ventilate the patient and necessitates reintubation. Changing the endotracheal tube in critically ill patients is facilitated by use of a semirigid tube exchanger. Commercial tube exchangers are hollow and allow oxygen insufflation.

Intubation bypasses the normal filtering function of the upper airway, allowing contaminated aerosols to enter the lower respiratory tract. Intubation also bypasses the ability of the upper airway to warm and humidify the inspired gas. Bypass of the glottis with an artificial airway may result in a decrease in functional residual capacity. Although a positive end-expiratory pressure (PEEP) of 3 to 5 cm H₂O may be useful to maintain functional residual capacity in intubated patients, there is no basis for the term "physiologic PEEP." Bypass of the upper airway may be problematic in the patient with chronic obstructive pulmonary disease (COPD) due to inability to control exhalation by use of pursed lips.

The flow resistance through an endotracheal tube is greater than that through the native airway. Some clinicians use a low level of pressure support or tube compensation during a spontaneous breathing trial to overcome the resistance through the endotracheal tube. However, with a usual adult-size endotracheal tube and a minute ventilation compatible with spontaneous breathing, the resistance of the endotracheal tube may not be clinically important. Because of airway edema, the resistance through the endotracheal tube may be similar to the resistance through the upper airway following extubation. Nonetheless, prolonged spontaneous breathing through a small endotracheal tube is not desirable and should be supported with pressure support or tube compensation.

Evaluation for Extubation

In many patients, extubation occurs when ventilatory support is no longer necessary. However, some patients need an artificial airway even though ventilatory support is no longer required. These include patients with upper airway obstruction, those unable to adequately clear secretions, and those unable to protect the lower respiratory tract from aspiration. Patients with a weak cough are five times more likely to fail extubation, patients with a large quantity of secretions are three times more likely to fail extubation, and patients who are unable to complete four simple tasks (open eyes, follow with eyes, grasp hand, stick out tongue) are four times as likely to fail extubation. Patients with any two of these risks are nearly seven time more likely to fail extubation.

One concern before extubation is whether the upper airway is free of swelling and inflammation. This is often assessed as the amount of leak around the endotracheal tube during positive pressure ventilation with the cuff deflated (leak test). Although patients who develop upper airway obstruction after extubation may have a failed leak test, absence of a leak with the cuff deflated may also occur in many patients who are successfully extubated.

Complications of Extubation

Complications of extubation are listed in Table 33-3. Failed extubation occurs in 10% to 25% of patients. Noninvasive ventilation reduces the rate of reintubation in patients at risk for extubation failure. Hoarseness is common after extubation and is usually short term and benign. For postextubation stridor due to upper airway swelling, cool mist therapy, aerosolized racemic epinephrine, parenteral steroids, and heliox therapy can be used. These treatments are only useful, however, for acute reversible swelling that responds relatively quickly to therapy. For irreversible postextubation obstruction (eg, vocal cord paralysis), the patient must be reintubated and tracheostomy may be required.

Timing of Tracheostomy

There are both advantages and disadvantages of tracheostomy compared with translaryngeal intubation (Table 33-4). No clear evidence or consensus exists for when a tracheostomy should replace an endotracheal tube. Using percutaneous techniques, the modern tracheostomy procedure is a relatively simple bedside procedure. Although many patients tolerate endotracheal intubation for weeks without complications, prolonged intubation increases the risk of glottic injury. On the other hand, tracheostomy increases the risk of tracheal stenosis. Tracheostomy is usually reserved for patients requiring long-term ventilatory support and for those needing long-term airway protection (eg, patients with neurologic disease) or those with multiple failed attempts to extubate. Some failure-to-wean patients may be successfully liberated from mechanical ventilation after tracheostomy. This may relate to less resistance through the tracheostomy tube, less dead space, increased ability to remove secretions, and improved patient comfort.

Types of Tracheostomy Tubes

Tracheostomy tubes are available in a variety of sizes and styles from several manufacturers. The dimensions of tracheostomy tubes are given by their inner diameter, outer diameter, length, and curvature. Proper fit of the tube is an important consideration, as a poorly fitting tube can lead to distal obstruction in the trachea and the formation of granulation tissue. Tracheostomy tubes can be angled or curved to improve the fit of the tube in the trachea. Extra proximal length tubes facilitate placement in patients with large necks, and extra distal length tubes facilitate placement in patients with tracheal anomalies. Some tubes have a spiral wire reinforced flexible design, and some have an adjustable flange design to allow bedside adjustments to meet extra length tracheostomy tube needs. An inner cannula is used on some tracheostomy tube designs. The inner cannula can be removed for cleaning. Cuffs on tracheostomy tubes include high-volume low-pressure cuffs, tight-to-shaft cuffs, and foam cuffs. The fenestrated tracheostomy tube has an opening in the posterior portion of the tube, above the cuff, which allows the patient to breathe through the upper airway when the inner cannula is removed. Some tracheostomy tubes have a port above the cuff that allows subglottic aspiration of secretions.

Speaking With a Tracheostomy Tube

For mechanically ventilated patients with a tracheostomy, the cuff is deflated and the leak that results through the upper airway can be used to facilitate speech. Good-quality voice can result in many patients by using higher levels of PEEP (which increases leak during exhalation), a longer inspiratory time, and a higher tidal volume set on the ventilator to compensate for the volume lost due to leak. For many patients voice quality is adequate without the need for a speaking valve, improving safety if the upper airway becomes obstructed when a speaking valve is used.

A speaking valve allows the patient to inhale through the tracheostomy tube but exhale through the upper airway. A speaking valve is more commonly used when the patient no longer requires positive pressure ventilation. When a speaking valve is placed, it is important that the patient can adequately exhale through the upper airway. This can be assessed by measurement of tracheal pressure when the valve is placed. If the expiratory tracheal pressure is greater than 10 cm H₂O, the placement of a smaller tube or the presence of upper airway pathology should be considered.

For patients who do not tolerate cuff deflation, a speaking tracheostomy tube can be used. With this tube, gas flow is introduced above the cuff to provide flow past the vocal cords and, thus, allow speech. Cuff deflation, with or without a speaking valve, usually produces better voice than a speaking tracheostomy tube.

Decannulation

In patients no longer requiring mechanical ventilation, level of consciousness, cough effectiveness, secretions, and oxygenation are considered important determinants of decannulation readiness. A stepwise approach is usually followed. The patient is first observed for tolerance of cuff deflation, followed by tolerance of a speaking valve and tolerance of capping. If the patient tolerates a capped tracheostomy tube for 24 to 72 hours, strong consideration should be given to decannulation. Decannulation failure is commonly defined as the need to reinsert an artificial airway within 48 to 96 hours following planned tracheostomy removal.

Alternative airway management equipment includes esophageal obturator airways, pharyngotracheal lumen airways, and esophageal-tracheal Combitubes. These devices, however, should not be used beyond the period of initial resuscitation. Another supraglottic airway is the laryngeal mask airway. It is inserted without a laryngoscope and has an inflatable rim that provides a low-pressure seal over the glottic opening. It is used for short-term ventilation when an intubated airway cannot be secured, and should be changed to an endotracheal tube as soon as possible. Video laryngoscopy can be used to accomplish endotracheal intubation. Video laryngoscopes are grouped into three different designs: stylets, guide channels, and video modifications of the traditional (usually Macintosh) laryngoscope blades.