Elevating the Head of the bed
Elevating the head of the bed is the most widely practiced pneumonia prevention strategy in the United States and much of the world. Over 98% of US hospitals report routinely elevating the head of the bed of patients on mechanical ventilation to prevent VAP. Notwithstanding widespread adoption of this practice, the evidence associating head-of-bed elevation with better outcomes is surprisingly sparse. Only three randomized controlled trials have been published in the English language literature.[46–48] The first trial only included 86 patients but reported significantly fewer VAPs in patients randomized to head-of-bed elevation (8 vs. 34%). The second trial only included 30 patients and found numerically fewer VAPs in the intervention group but the effect was not statistically significant. The third and most rigorous study to date included 221 patients and found no difference in VAP rates between patients randomized to 45 degrees head-of-bed elevation versus 10 degrees. Importantly, this study included continuous measures of backrest elevation and reported that the ICU team had difficulty in both achieving and maintaining the target backrest elevation position: initial average backrest elevation in the intervention group was 28 degrees and decreased to 23 degrees by day 7. While this may account for this study's lack of impact on VAP rates, it also attests to the practical difficulties ICUs face with achieving reliable backrest elevation.
Of note, none of the three studies reported any differences in corollary outcomes such as duration of mechanical ventilation, ICU length of stay, or mortality.[46–48] Chinese investigators subsequently published a Cochrane review that included these three studies plus five additional randomized trials from the Chinese language literature. Even with these additional studies, however, there were only 739 patients available for evaluation. On meta-analysis amongst these patients, backrest elevation was associated with a significant drop in VAP incidence (14 vs. 40%, risk ratio [RR]: 0.36; 95% confidence interval [CI]: 0.25–0.50). Only a subset of the studies in the meta-analysis included data on other outcomes: collectively they found no significant differences in ICU length of stay or mortality (3 studies, 346 patients).
Notably, some investigators have challenged the notion that elevating the head of the bed is the best way to prevent VAP. Li Bassi and colleagues hypothesized that the lateral Trendelenburg position may be a more effective station to prevent VAP since this position uses gravity to draw orogastric secretions in the upper aerodigestive tract away from the lungs rather than facilitating their entry into the lungs. They tested this hypothesis by randomizing 401 patients to the lateral Trendelenburg position versus the semirecumbent position. Patients randomized to the lateral Trendelenburg position did indeed develop fewer microbiologically confirmed VAPs (0.5 vs. 4.0%) but the trial was stopped early because of a higher rate of serious adverse events amongst patients randomized to the lateral Trendelenburg position including oxygen desaturation, severe hypotension, sustained bradycardia, extubation, intracranial hemorrhage, and brachial plexus injury.
Despite the lack of robust data supporting the semirecumbent position, practitioners are still advised to elevate the head of the bed whenever safe and feasible to do so. This is because of observational data showing a strong association between the supine position and VAP particularly in patients receiving enteral nutrition, radiolabeling and orogastric biomarker studies documenting that ventilated patients routinely aspirate oropharyngeal and gastric secretions, and observational studies of ventilator bundle components suggesting that head-of-bed elevation may indeed be associated with shortening duration of mechanical ventilation.[31,46,53–55] All told this intervention is already ubiquitous in practice, inexpensive, possibly helpful, and unlikely to be harmful for most patients.
Semin Respir Crit Care Med. 2019;40(4):548-557. © 2019 Thieme Medical Publishers