The Ventilator-Dependent Patient
This chapter describes the daily care and concerns for ventilator-dependent patients, with emphasis on the artificial airways (endotracheal and tracheostomy tubes) and mechanical complications of positive pressure ventilation. The infectious complications of mechanical ventilation are described in Chapter 16.
I. Artificial Airways
A. Endotracheal Tubes
Endotracheal (ET) tubes vary in length from 25 to 35 cm, and are sized according to their internal diameter (ID), which varies from 5 to 10 mm (e.g., a “size 7” endotracheal tube indicates an ID of 7 mm). A size 8 ET tube (ID = 8 mm) is standard for adults (1).
1. Subglottic Drainage Tube
The prominent role played by aspiration of mouth secretions in ventilator-associated pneumonias has led to the introduction of specially-designed ET tubes capable of draining mouth secretions that accumulate just above the inflated cuff (see Chapter 16, Figure 16.1). These tubes can reduce the incidence of ventilator-associated pneumonia (2), and should be considered when intubating patients who are likely to require more than 48 hours of ventilatory support.
2. Tube Position
Evaluation of tube position is mandatory after intubation, and Figure 21.1 shows the proper tube position. When the head is in a neutral position, the tip of the ET tube should be 3 to 5 cm above the carina, or midway between the carina and vocal cords. (If not visible, the main carina is usually over the T4–T5 interspace.)
ET tubes can migrate into the right mainstem bronchus (which runs a straight course down from the trachea). To reduce the risk of this complication, keep the tip of the endotracheal tube no further than 21 cm from the teeth in women, or 23 cm in men (3).
 FIGURE 21.1 Portable chest x-ray showing proper position of an endotracheal tube, with the tip of the tube located midway between the thoracic inlet and the carina. |
3. Laryngeal Injury
The risk for laryngeal injury from ET tubes is a major
concern, and is one of the reasons for performing tracheostomies when prolonged intubation is anticipated. The spectrum of laryngeal damage includes ulceration, granulomas, vocal cord paresis, and laryngeal edema.
concern, and is one of the reasons for performing tracheostomies when prolonged intubation is anticipated. The spectrum of laryngeal damage includes ulceration, granulomas, vocal cord paresis, and laryngeal edema.
Laryngeal injuries are reported in three-quarters of patients who are intubated for longer than 24 hours (4), but most cases are not clinically significant, and do not result in permanent injury (5).
Airway obstruction from laryngeal edema is reported after 13% of extubations (4). (The management of this problem is described in Chapter 22.)
B. Tracheostomy
Tracheostomy is preferred in patients who require prolonged mechanical ventilation (>1–2 weeks). There are several ad-vantages with tracheostomy, including greater patient comfort, easier access to airways for clearing secretions and bronchodilator administration, reduced resistance for breathing, and reduced risk of laryngeal injury.
1. Timing
The optimal time for performing a tracheostomy has been debated for years. Recent studies comparing early tracheostomy (one week after intubation) with late tracheostomy (two weeks after intubation) have shown that early tracheostomy reduces sedative requirements and promotes early mobilization (6), but does not reduce the incidence of ventilator-associated pneumonia, or the mortality rate (6,7).
Based on the pneumonia and mortality data, tracheostomy is recommended after 2 weeks of endotracheal intubation (8). However, if one considers patient comfort, it is reasonable to consider tracheostomy after 7 days of intubation if there is little chance of extubation in the next few days.
2. Complications
Percutaneous dilatational tracheostomy is associated with less blood loss and fewer local infections than surgically created tracheostomies (9).
Combining surgical and percutaneous tracheostomy, the mortality rate is <1%, and early complications (i.e., bleeding and infection) occur in <5% of cases (9,10).
TRACHEAL STENOSIS: Tracheal stenosis is a late complication that appears in the first 6 months after the tracheostomy tube is removed. Most cases of tracheal stenosis occur at the site of the tracheal incision, and are the result of tracheal narrowing after the stoma closes. The incidence of tracheal stenosis ranges from zero to 15% (10), but most cases are asymptomatic. The risk of tracheal stenosis is the same with surgical and percutaneous tracheostomies (8).
C. Cuff Management
Artificial airways are equipped with inflatable balloons (called cuffs) that are used to seal the trachea and prevent gas from escaping through the larynx during lung inflation. A tracheostomy tube with an inflated cuff is shown in Figure 21.2. Note the elongated design of the cuff, which allows for greater dispersion of pressure, and allows a tracheal seal at relatively low pressures.
1. Cuff Inflation
The cuff is attached to a pilot balloon that has a one-way valve. To inflate the cuff, a syringe is attached to the pilot balloon, and air is injected into the cuff through the pilot balloon (which will inflate as the cuff inflates).
The cuff is inflated until no audible leak is detected around the cuff.
The pressure in the cuff (measured with a pressure gauge attacmhed to the pilot balloon) should be <25 mm
Hg (11), which is the assumed hydrostatic pressure in capillaries within the wall of the trachea. (Cuff pressures >25 mm Hg could then compress adjacent capillaries and produce ischemic injury in the trachea.)
 FIGURE 21.2 A tracheostomy tube with an inflated cuff. See text for further explanation. |
2. Cuff Leaks
Cuff leaks are usually detected by audible sounds during lung inflation (created by gas escaping through the
vocal cords). The volume of the leak is the difference between the desired tidal volume and the exhaled tidal volume. Cuff leaks are rarely caused by disruption of the cuff (12), and are usually the result of nonuniform contact between the cuff and the wall of the trachea, or a leaky valve on the pilot balloon causing cuff deflation.
vocal cords). The volume of the leak is the difference between the desired tidal volume and the exhaled tidal volume. Cuff leaks are rarely caused by disruption of the cuff (12), and are usually the result of nonuniform contact between the cuff and the wall of the trachea, or a leaky valve on the pilot balloon causing cuff deflation.
3. Troubleshooting a Cuff Leak
If a cuff leak is audible, detach the patient from the ventilator and inflate the lungs manually with an anesthesia bag (keeping the end-tidal PCO2 at the baseline level). Then check the pilot balloon, and proceed as follows:
If the pilot balloon is deflated, the problem is a tear in the cuff, or an incompetent valve in the pilot balloon. Inflate the pilot balloon and keep the syringe attached. If the pilot balloon deflates with the syringe attached, the problem is a cuff tear (and the tube should be replaced immediately), and if the pilot balloon remains inflated and the leak disappears, the problem is an incompetent valve in the pilot balloon (which can be quickly remedied by clamping the narrow tube between the pilot balloon and cuff, pending replacement of the tracheal tube).Related posts:
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