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The use of a small tidal volume regime compared to a traditional tidal volume regime in all-comers with ARDS

 

 

There was no benefit in mortality but the intervention was shown to be safe when comparing a small tidal volume ventilatory regime over traditional tidal volumes in all comers with ARDS requiring ventilation

Level of Evidence 1-

 

Citation/s:
 Browler RG, et al. Prospective, randomized, controlled clinical trial comparing traditional vesus reduced tidal volume ventilation in acute respiratory distress syndrome patients. Crit Care Med 1999;27:1492-8


Lead author's name and fax: BrowerRG

 

Three-part Clinical Question:

1.      Patients- Patients with ARDS according to the American European Consensus definition requiring mechanical ventilation

2.      The treatment- Small tidal volume ventilation 8ml/kg versus 10-12 ml/kg

3.      The outcome- Time to reversal of respiratory failure

Search Terms: ARDS- therapy Prospective studies/ randomised studies/ random allocation Double blind method

 

The Study:
Non-blinded concealed randomised controlled trial without intention-to-treat.


The Study Patients: ARDS according to the American European Consensus Conference definition requiring mechanical ventilation


Control group (N = 26; 26 analysed): Initial stabilisation period followed by a complex algorithm Initial tidal volume 10-12ml/kg (body weight according to nomogram) Vt remained at this level unless Pplat < 45 -55cmH2O SaO2 target 86-94% using PEEP or FiO2 manipulation according to schemata Acid-base- Resp rate adjusted to get PaCO2 4.0-6.0kPa to max rate of 30/min then bicarbonate infusion Continued for 28 days or until primary end point achieved


Experimental group (N = 26; 26 analysed): Initial stabilisation followed by algorithm Initial tidal volume 8ml/kg (body weight according to nomogram) VT then reduced incrementally in increments of 0.5ml/kg in intervals of 3-6 hours until Pplat < 30cmH2O. Further reduction if P plat again > 30cmH2O SaO2, Acid base, PaCO2 duration of treatment targets as for control group

 

The Evidence:

Outcome

Time to Outcome

CER

EER

RRR

ARR

NNT

Time to reversal of respiratory failure

ICU

0.58

0.58

0%

0.000

INF

95% Confidence Intervals:

-46% to 46%

-0.268 to 0.268

NNT = 4 to INF; NNH = 4 to INF

Mortality

Hospital

0.462

0.500

-8%

-0.038

-26

95% Confidence Intervals:

-67% to 51%

-0.309 to 0.233

NNT = 4 to INF; NNH = 3 to INF

 

Comments:
This study failed to exclude bias by not blinding or carrying out an intention to treat analysis. They stopped the study early so they could join another study and failed to demonstrate a reduction in their primary outcome measure of reversal of respiratory failure.

 

EBM summary questions:

  1. Do the methods allow the adequate testing of the hypothesis- No the study was stopped prematurely to join another study and failed to demonstrate a reduction in their primary outcome measure of reversal of respiratory failure.

  2. Do the statistical tests correctly test the results to allow differentiation of statistically significant result- No, again the lack of power means that they did not reach the calculated power calculation number and thus failed to demonstrate the primary outcome

  3. Are conclusions valid in light of results- They have stated that they found the STV was safe due to lack of difference in PEEP, FiO2, sedation requirements, circulatory requirements and had a similar outcome but had no benefits. They also concluded that a positive outcome in terms of their primary outcome measure was unlikely to be obtained. This could be because a greater difference between trial groups may help differentiate a clinical significant outcome and this was built into the ARDSnet study; there was insufficient power; there was no treatment effect. 

  4. Did results get omitted, and why- They seemed to analyse all patients and present all relevant results.

  5. Did they suggest areas of further research- As above they suggested to reduce Vt and  Pplat more aggressively in further studies

  6. Did they make recommendations based on results and were they appropriate- They recommended further research and did not recommend adoption of this strategy.

  7. Is this study relevant to my clinical practice- Yes, it seems to be relevant group of patients but as it lacks an important outcome benefit it would not be applied.

  8. What level of evidence does this study represent- Level 1 negative

  9. What grade of recommendation can I make on this result alone- No recommendation

  10. What grade of recommendation can I make when this study is considered along with other available evidence- Grade A recommendation

  11. Should I change my practice because of these results- No, not from this result.

  12. Should I audit my current practice because of these results- No, not from these results but in terms of future results in this area.

 

 

Appraised by: Brian H Cuthbertson, Intensive Therapy Unit, Aberdeen Royal Infirmary ; Monday, November 04, 2002
Email: b.h.cuthbertson@abdn.ac.uk
Kill or Update By: 3rd November 2005

 

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