Prevention of Intensive Care Unit-acquired Pneumonia

Michael Klompas, MD, MPH

Disclosures

Semin Respir Crit Care Med. 2019;40(4):548-557. 

In This Article

Subglottic Secretion Drainage

Subglottic secretion drainage has received a great deal of attention as a potential strategy to prevent VAP.[63] Secretions pooling above the endotracheal tube cuff create an inflammatory milieu where excess mucin production can impair host defenses and create a reservoir for pathogenic organisms that can seep across the endotracheal tube cuff and infect the lungs.[64] Routine or continuous drainage of subglottic secretions would therefore appear to be an attractive strategy to mitigate this risk. Multiple studies both in isolation and on meta-analysis have reported that subglottic secretion drainage may lower VAP rates by as much as 45%.[65–69] The corollary data on objective outcomes, however, are complicated and contradictory.

Initial meta-analyses reported that subglottic secretion drainage was associated with a significant decrease in duration of mechanical ventilation and ICU length of stay in addition to VAP.[65–67] On the basis of these encouraging corollary outcomes, the Society for Healthcare Epidemiology of America recommended subglottic secretion drainage as a basic strategy to prevent VAP in 2014.[20] On re-evaluation of the supporting data, however, the meta-analyses suggesting significant decreases in duration of mechanical ventilation and ICU length of stay had high levels of heterogeneity suggesting large discrepancies in the underlying populations, methods, or reporting of component studies (indeed, one key study was abstracted as showing a large decrease in mean duration of mechanical ventilation,[67] whereas the original trial reported no difference in this outcome[70]). When the meta-analysis was updated by excluding questionable studies and adding some newly published studies, the positive association between subglottic secretion drainage and lower VAP rates remained but there was no longer any association between subglottic secretion drainage and improvements in duration of mechanical ventilation, ventilator-associated events, ICU length of stay, or mortality.[69]

Subglottic secretion drainage, like most VAP prevention initiatives, is at high risk of bias in prevention studies because removing subglottic secretions can decrease the perceived volume and frequency of pulmonary secretions and possibly lower microbial colonization rates. These in turn may lead to fewer patients in the intervention arm that meet VAP surveillance criteria, but these criteria are not specific for histological pneumonia so it is possible to see lower rates of perceived pneumonia that might not correspond to a true decrease in invasive disease.[13,71] The lack of a clear association between subglottic secretion drainage and objective outcomes suggests that this intervention should be treated with caution, particularly as there are some downsides to subglottic secretion drainage tubes including larger external diameters compared with similar caliber conventional tubes, increased risk for clogging, and higher cost.

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