Subglottic Secretion Drainage for Preventing Ventilator-Associated Pneumonia

Abstract & Commentray

By Dean R. Hess, PhD, RRT

Respiratory Care, Massachusettes General Hospital, Department of Anesthesiology, Harvard Medical School

Dr. Hess reports no consultant, stockholder, speaker’s bureau, research, or other financial relationships with compaines having ties to this field.

Synopsis: Subglottic secretion drainage appears effective in preventing early onset ventilator-associated pneumonia among patients expected to require > 72 hours of mechanical ventilation.

Source: Dezfulian C, et al. Subglottic Secretion Drainage for Preventing Ventilator-Associated Pneumonia. Am J Med. 2005;118:11-18.

The purpose of this meta-analysis was to assess the efficacy of subglottic secretion drainage in preventing ventilator-associated pneumonia (VAP). Dezfulian and colleagues performed a comprehensive analysis of randomized trials that have compared subglottic secretion drainage with a standard endotracheal tube care in mechanically ventilated patients. Studies were identified by searching computerized databases (MEDLINE, CINAHL, EMBASE, Cochrane Library, Current Contents, and Biological Abstracts), reviewing bibliographies, and expert consultation. Summary risk ratios and weighted mean differences with 95% confidence intervals were calculated for each outcome using a fixed-effects model.

Of 110 studies retrieved, 5 met the inclusion criteria of mechanically ventilated patients prospectively assigned randomly to some form of subglottic secretion drainage vs no drainage (control), and also that the incidence of pneumonia was reported in both groups. The 5 studies enrolled 896 patients. Subglottic secretion drainage reduced the incidence of VAP by nearly half (risk ratio = 0.51; 95% confidence interval [CI], 0.37-0.71), primarily by reducing early onset pneumonia (pneumonia occurring within 5 to 7 days after intubation). Although significant heterogeneity was found for several end points, this was largely resolved by excluding a single outlying study. The outlier study recruited cardiac surgery patients whose duration of mechanical ventilation (mean, 1.5 days) was shorter than the other studies.

The method of subglottic secretion drainage was intermittent suction in 2 studies, continuous 2 studies, and hourly aspiration with a syringe in the remaining study. In the 4 studies other than the outlier, subglottic secretion drainage shortened the duration of mechanical ventilation by 2 days (95% CI, 1.7-2.3 days) and the length of stay in the ICU by 3 days (95% CI, 2.1-3.9 days), and delayed the onset of pneumonia by 6.8 days (95% CI, 5.5-8.1 days). Dezfulian et al concluded that subglottic secretion drainage appears to be effective in preventing early onset VAP among patients expected to require > 72 hours of mechanical ventilation.

Commentary

VAP is an important clinical problem. It has been reported to occur in about 10% of mechanically ventilated patients.1 Although its impact on mortality is debated, there is no question that it increases morbidity by increasing the requirement for antibiotic therapy, and also by increasing the time on mechanical ventilation and days in the ICU. The term ventilator-associated pneumonia is misleading, as it is well accepted that VAP arises most commonly due to micro-aspiration of pharyngeal secretions around the cuff of the endotracheal tube rather what is breathed through the endotracheal tube from the ventilator. Accordingly, a method to prevent micro-aspiration might be expected to reduce the incidence of VAP.

Many practices have been identified to prevent VAP.2 One such practice is subglottic secretion drainage. Subglottic secretion drainage is accomplished through use of a specially designed endotracheal tube with a separate dorsal lumen that opens directly above the endotracheal tube cuff. Although originally designed for use with an endotracheal tube, it is also now available in the design of some tracheostomy tubes.

The results of this meta-analysis suggest a strong benefit for the use of subglottic secretion drainage to prevent early onset VAP. However, there are several issues that remain to be resolved before this practice can be widely adopted. The benefit of subglottic secretion clearance is in patients who require > 72 hrs of mechanical ventilation. Unfortunately, it is difficult to predict which patients will require > 72 hrs of mechanical ventilation at the time of intubation. Because tubes capable of providing subglottic secretion clearance cost about 10 times more than standard endotracheal tubes, it is likely not cost-effective to use these tubes in all patients who are intubated. Moreover, patients should generally not be reintubated with this tube if they require > 72 hrs of ventilation, as reintubation itself is a risk factor for VAP.

The safety of these tubes is yet to be determined. In an animal study, tracheal wall injury due to subglottic suction was reported.3 However, whether similar injury occurs in humans is unknown; this complication was not reported in any of the studies included in the meta-analysis reported here. The higher rigidity of the endotracheal tube incorporating subglottic suction may contribute to tracheo-innominate artery fistula4 and upper airway edema.

Finally, the cost-effectiveness of these tubes remains to be determined. Their use does not appear to affect mortality, but this meta-analysis suggests that ventilator days and ICU days may be reduced. A formal economic assessment of these devices would help to answer the question of cost-effectiveness. To my knowledge, such an analysis is not yet available, although it has been suggested that the use of subglottic suction can be supported on the basis of the cost of VAP.5

There is no doubt that aspiration of subglottic secretions decreases the risk of early-onset VAP. Appropriate patient selection for this procedure, however, remains elusive. Until the cost-effectiveness of endotracheal tubes with a subglottic suction port is established, their use will likely not become standard practice. The finding of lower rates of VAP with the use of this procedure does support the fact that VAP often arises from micro-aspiration of secretions around the cuff of the airway.