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Abstract & Commentary
By Eric C. Walter, MD, MSc
Pulmonary and Critical Care Medicine, Northwest Permanente and Kaiser Sunnyside Medical Center, Portland
Dr. Walter reports no financial relationships relevant to this field of study.
SYNOPSIS: Prone positioning appears to be associated with a higher incidence of pressure ulcers in patients with severe acute respiratory distress syndrome.
Recently, the Proseva trial showed a 50% reduction in mortality in patients with
severe acute respiratory distress syndrome (ARDS) who underwent prone positioning compared to patients kept supine.1 Prone positioning was not reported to have any difference in adverse events. Although not listed as an adverse event, the development of pressure sores required proning interruption in 16 patients (6.8%).1 Girard and colleagues now present a secondary analysis of the Proseva study to compare the incidence and severity of pressure ulcers and to determine if pressure ulcer development was due to body position or better survival.
All patients in Proseva had severe ARDS (PaO2/FiO2 ratio of < 150 mmHg, with an FiO2 of ≥ 0.6, positive end-expiratory pressure ≥ 5 cm H2O). Patients were randomized to either the prone position for at least 16 hours per day (n = 237) or to remaining supine (n = 229). Standard ICU beds were used for all patients. The patients’ knees, forehead, chest, and iliac crests were protected using adhesive pads. The number of pressure ulcers did not differ between groups at the time of study entry. By day 7, more patients had pressure ulcers in the prone group compared to the supine group (57.1% vs 42.5%, P = 0.005). As would be expected, pressure ulcers on the face and anterior thorax were more common in the prone group than the supine group. At the time of ICU discharge, the total number of patients with pressure ulcers did not differ between the prone and supine groups (37.8% vs 44.4%, P = 0.151). However, pressure ulcers on the face and anterior thorax remained more common in the prone group (18.4% vs 1.4%, P < 0.0001 and 6.4% vs 0.9%, P = 0.0025, respectively).
The incidence of new patients with pressure ulcers over time was analyzed in several ways. In all analyses, new pressure ulcers were more common among patients in the prone group than in the supine group. The differences were most striking in the first 7 days. These differences narrowed and were no longer always significantly different by ICU discharge. Risk factors for development of pressure ulcers included age, male gender, increased body mass index, and increased severity of illness. In a multivariate analysis accounting for the above risk factors, the odds ratio for development of a pressure ulcer of stage 2 or greater was 1.54 (95% confidence interval, 0.97-2.44; P = 0.0653).
The Proseva trial generated excitement given the dramatic reduction in mortality among patients randomized to prone positioning. Girard and colleagues are commended in reminding us of the potential complications of this procedure. However, there are some points that should be considered when interpreting these data. In both groups the development of pressure ulcers was strikingly high, the authors evaluated pressure ulcers at multiple locations at multiple time points, and the incidence of new pressure ulcers was evaluated 16 different ways. Some incidence analyses used the number of new patients with pressure ulcers and others used the number of new pressure ulcers. There were two different definitions of pressure ulcer (any pressure ulcer vs stage 2 or greater pressure ulcers). Finally, the incidence was calculated two different ways: per 1000 days of ventilation and per 1000 ICU days.
This led to different results, even for the stated primary endpoint of "the incidence of new patients with pressure ulcers at stage 2 or higher from day 1 to ICU discharge." In one analysis, the difference was significant but not the other. With such different evaluations, caution is warranted, as statistically significant results could be simply due to chance. The authors also concluded that the increased risk of pressure ulcers was in part due to the improved survival among patients who were proned. While this may be a reasonable hypothesis, I am not convinced the data they present can answer this important question.
However, even with the above considerations, it seems more likely than not that prone positioning was associated with an increased risk of pressure ulcers. Many of the authors’ observations make intuitive sense, such as that in patients who were proned, pressure ulcers were more frequent on anterior body parts and less frequent on posterior body parts. The reverse was true for patients kept supine. Furthermore, while not always significant, the direction of effect was the same in all of the incidence analyses: The incidence of pressure ulcers was consistently greater among patients who were proned compared to those who were supine.
The increased survival associated with proning clearly outweighs the risk of pressure ulcers, but critical care practioners should be aware of this risk, especially since severe pressure ulcers are described as a serious reportable event in health care (so-called "never events") by the National Quality Forum.2
1. Guerin C, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013;368:2159-2168.
2. National Quality Forum (NQF). Serious reportable events in health-care-2011 update: A consensus report. Washington, DC: NQF; 2011.