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ARDS: Prone positioning has no effect on mortality

 

In patients with ARDS, prone positioning improves oxygenation but has no impact on mortality, except perhaps in those with SAPS >50 

Level of Evidence: 1+ (SR based on small RCTs, conducted prior to ARDSnet – subsequent change in practise)

 Citation/s: Alsaghir AH, et al. Effect of prone positioning in patients with acute  respiratory distress syndrome: a meta-analysis. Crit Care Med. 2008 Feb;36(2):603-9.

Lead author: Abdullah HE-mail-cmartin1@uwo.ca

 Three-part Clinical Question:

1)      Patients: Adults with ARDS.

2)      Intevention: Prone positioning.

3)      Outcome: Primary: Mortality, Secondary: improvement in oxygenation, duration of mechanical ventilation and incidence of ventilator associated pneumonia.


Search Terms: 1. exp Respiratory Distress Syndrome, Adult/ (2626), 2. (acute respiratory distre$ or ARDS).tw. (1861), 3 1 or 2 (3309), 4 exp Prone Position/ (575), 5 prone posit$.tw. (611), 6. 4 or 5 (877), 7. 3 and 6 (117), 8. SR filter (303616), 9. 7 and 8 (50)

 

The Review:
Data Sources: : Cochrane Library, Medline, Embase, hand search, mail shot,
Study Selection: Included only RCT's in human adults
Data Extraction: Trials limited to adult mechanically ventilated ICU patients comparing supine and prone positioning. Prone positioning had to be used for at least 6hrs. Outcome measures were mortality, improvement in oxygenation, duration of mechanical ventilation and incidence of ventilator associated pneumonia.

The studies were multiple independent reviews of individual reports. They were tested for heterogeneity.

 

The Evidence:

 

 

Outcome

Time to Outcome

Typical CER

Typical OR

RRR

NNT

p Value

Mortality

ICU mortality

0.32

0.79

15%

∞

 

95% Confidence Intervals:

0.45 to 1.39

 

 

 

 

Sub-group Analysis

 

Sub-group

CER

OR

RRR

NNT

mortality SAPS >50

0.50

0.29

55%

4

95% Confidence Intervals:

0.12 to 0.7

 

3 to 11

It was not apparent whether this sub-group analysis was data-dependent or an a priori hypothesis. The analysis was clinically significant, made biological sense, was one of many SGAs, and was consistent in more than one RCT.

 There was no difference in the number of ventilator days or on the incidence of ventilator acquired pneumonia between the two groups (prone and supine positioning)

 There was a significant improvement in both early and late oxygenation in the prone positioning groups, with a WMD (weighted mean difference) in PaO2/FiO2 ratio of 43.87 (95% CI 13.86-73.88) and 24.89 (95% CI 15.3-34.48) respectively.

 Comments:
(i) In the patients with SAPS >50, the two studies which demonstrated an improvement in mortality had different time scales. (ii) Most of the studies had relatively short duration of prone positioning. (iii) Two of the studies (including the largest and one which reported improvement in mortality in higher severity of illness subgroup) used larger Vt than recommended as they were done pre-ARDSnet. (iii) The groups were very heterogeneous

 EBM Comments: 

1)      Do the methods allow accurate testing of the hypothesis? Yes, it was a thorough meta-analysis of the available evidence. 

2)      Do the statistical tests correctly test the results to allow differentiation of statistically significant results? Yes. 

3)      Are the calculations valid in the light of the results? Yes 

4)      Did results get omitted and why? No. 

5)      Did they suggest other areas of research? Yes, suggested a RCT in high illness severity patients to refute/confirm the subgroup analysis. 

6)      Did they make any recommendations based on the results and were they appropriate? Yes, recommended considering early proning in high illness severity patients based on little harm and low expense-this was not unreasonable although the evidence of mortality benefit is not strong. 

7)      Is the study relevant to my clinical practice?  Yes-proning is common 

8)      What level of evidence does the study represent?  1+ 

9)      What grade of recommendation can I make on this result alone? B 

10)  What grade of recommendation can I make when this study is considered along with other available evidence? B 

11)  Should I change my practice because of these results? Probably not.  Showed neither harm nor any firm benefit of proning but one could consider earlier in the most severely ill patients in whom oxygenation is difficult. 

12)  Should I audit my current practice because of these results? No-there is still no gold standard to compare against

 

Appraised by: Alex Puxty Department of Anaesthesia Glasgow Royal Infirmary, Glasgow
Email: apuxty@doctors.org.uk



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