Effect of prone positioning on the survival of patients with acute respiratory failure
This review may be edited
Posted By: Gordon S. Doig
Posted Date: 11Sept2001
Title: Effect of prone positioning on the survival of patients with acute respiratory failure
Authors: Gattinoni L, Tognoni G, Pesneti et al
Reference: NEJM 2001;345:568-573
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Abstract: BACKGROUND: Although placing patients with acute respiratory failure in a prone (face down) position improves their oxygenation 60 to 70 percent of the time, the effect on survival is not known.
METHODS: In a multicenter, randomized trial, we compared conventional treatment (in the supine position) of patients with acute lung injury or the acute respiratory distress syndrome with a predefined strategy of placing patients in a prone position for six or more hours daily for 10 days. We enrolled 304 patients, 152 in each group.
RESULTS: The mortality rate was 23.0 percent during the 10-day study period, 49.3 percent at the time of discharge from the intensive care unit, and 60.5 percent at 6 months. The relative risk of death in the prone group as compared with the supine group was 0.84 at the end of the study period (95 percent confidence interval, 0.56 to 1.27), 1.05 at the time of discharge from the intensive care unit (95 percent confidence interval, 0.84 to 1.32), and 1.06 at six months (95 percent confidence interval, 0.88 to 1.28). During the study period the mean (+/-SD) increase in the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen, measured each morning while patients were supine, was greater in the prone than the supine group (63.0+/-66.8 vs. 44.6+/-68.2, P=0.02). The incidence of complications related to positioning (such as pressure sores and accidental extubation) was similar in the two groups.
CONCLUSIONS: Although placing patients with acute respiratory failure in a prone position improves their oxygenation, it does not improve survival.
Are the Results Valid?
1. Was the assignment of patients to treatments randomized? ( Was allocation concealment maintained?)
Yes. The investigators describe the use of centralized telephone randomization.
2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?
2a. Was followup complete?
Yes. From a total of 152 patients per group, 6 month follow-up outcomes were not available in only 3 patients in the control group and 4 in the prone group.
2b. Were patients analyzed in the groups to which they were randomized?
Yes. Regardless of the intervention actually delivered (12 of the patients initially randomized to the supine management group were eventually proned due to the severity of arterial hypoxemia), a true intention-to-treat analysis was performed.
3. Were patients, health workers, and study personnel blind to treatment?
No. It would have been impossible to blind health workers with regards to the intervention without compromising patient safety.
4. Were the groups similar at the start of the trial?
Yes. Table 1 demonstrates good balance with regards to age, gender, SAPS II, Cause of lung injury and other organ failures.
5. Aside from the experimental intervention, were the groups treated equally?
Yes. Although cointerventions are not reported in a seperate table, there is no reason to suspect that patients were not treated equally during the trial.
What are the Results?
1. How large was the treatment effect?
There was a marginal, but non-significant decrease in mortality of 4% reported on day 10. This potential benefit had decreased to a 2% increase in mortality in the proning group by ICU discharge, which was maintained at the 6 month follow-up time.
2. How precise was the estimate of the treatment effect?
There were no significant benefits documented. As such, since this is a 'negative' clinical trial performed with an a priori power <80%, it is not possible to declare the two approaches equivalent.

Will the Results Help Me In Caring For My Patients?
1. Can the results be applied to my patient care?
No. Since this was an underpowered negative trial, it cannot provide evidence to stop the use of proning.

Post-hoc sub-group analysis shows that patients who are more sevely ill may benefit from proning, but this finding should be regarded as hypothesis generating and needs to be confirmed in a subsequent clinical trial directed towards only severly ill ARDS patients.

2. Were all clinically important outcomes considered?
Yes. The authors did an excellent job in using 6 month following-ups.
3. Are the likely treatment benefits worth the potential harms and costs?
Since this is an underpowered negative trial, it is hard to draw firm conclusions however, it is the first trial that I am aware of that documents a potential negative effect on mortality from proning (not significant, VERY small BUT nontheless, negative 2% mortality).

It is important to follow-up this trial to document benefits in sub-groups in which proning is currently used as routine care (i.e. more severly ill patients).

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Effect of prone positioning on the survival of patients with acute respiratory failure

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