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Low tidal volume in ARDS (ARDS net)

 

Treating 432 ARDS patients with low tidal volume ventilation (6ml/kg) reduced hospital mortality for all comers for ARDS from 39.8% to 31% (NNT 11) compared to high tidal volume (12ml/kg) ventilation

Level of Evidence 1++

 

Citation/s:
ARDSnet. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and acute respiratory distress syndrome. N Engl J Med 2000;342:1301-8


Lead author's name and fax: Anon (ARDS net)

 

Three-part Clinical Question:

 

1.      What patients- All comers with ARDS (American European Definition)

2.      What treatment- tidal volume limitation to 6ml/kg

3.      30 day mortality

 

Search Terms: ARDS; Ventilation; Mortality; Tidal volume limitation.

 

The Study:
Single-blinded concealed randomised controlled trial with intention-to-treat.


The Study Patients: ARDS according to American European Consensus definition with 10 Centres for 3 years


Control group (N = 429; 429 analysed): Vt set at 12ml/kg If Plateau pressure > 50cmH2O then reduced stepwise until plateau airway pressure < 50cmH2O. If plateau pressure < 45cmH2O then Vt increased by 1ml/kg until plateau pressure > 45cmH2O to maximum of 12ml/kg


Experimental group (N = 432; 432 analysed): Vt set at 6ml/kg. If plateau pressure > 30cmH2O then VT reduced by 1ml/kg until Plateau pressure < 30cmH2O to minimum Vt of 4ml/kg If plateau pressure < 25cmH2O the VT increased by 1ml/kg initial plateau pressure > 25cmH2O.

All other maneuvers same

The Evidence:

 

Outcome

Time to Outcome

CER

EER

RRR

ARR

NNT

Death

Hospital

0.399

0.308

23%

0.091

11

95% Confidence Intervals:

7% to 39%

0.027 to 0.155

6 to 36

Breathing without assistance

28 day

0.657

0.546

17%

0.111

9

95% Confidence Intervals:

7% to 27%

0.046 to 0.176

6 to 22

Ventilator free days

28 day

0.100

0.12

-20%

-0.020

-50

95% Confidence Intervals:

-62% to 22%

-0.062 to 0.022

NNT = 46 to INF; NNH = 16 to INF

 

Comments:


An well conducted well powered randomised controlled study demonstrating a clear reduction in mortality in all comers with ARDS. This study looks at similar patients with regard to age, sex, severity of illness and severity of lung injury but not racial mix to patients cared for in Scottish ICU's. It is applicable to our practice and should be adopted in its current form without requirement for further study. There is an ideal opportunity for retrospective comparison the SICS ARDS outcome data from 1999.

 

EBM summary questions:

 

  1. Do the methods allow the adequate testing of the hypothesis- Yes

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

  3. Are conclusions valid in light of results- Yes

  4. Did results get omitted, and why.- No

  5. Did they suggest areas of further research- No

  6. Did they make recommendations based on results and were they appropriate- Yes- that high priority should be given to preventing excessive lung stretch during adjustments to mechanical ventilation in ALI and ARDS.

  7. Is this study relevant to my clinical practice- Yes- this study looks at similar patients with regard to age, sex, severity of illness and severity of lung injury but not racial mix to patients cared for in Scottish ICU's.

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

  9. What grade of recommendation can I make on this result alone- A

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

  11. Should I change my practice because of these results- Yes

  12. Should I audit my current practice because of these results- Yes- There is an ideal opportunity for retrospective comparison the SICS ARDS outcome data from 1999.

 

Conclusions:

A well conducted, well-powered, randomised controlled study demonstrating a clear reduction in mortality in all comers with ALI and ARDS. It is applicable to our practice and should be adopted in its current form without requirement for further study.

 

Appraised by: Brian H Cuthbertson, Intensive Therapy Unit, Aberdeen Royal Infirmary; Aberdeen; Monday, September 17, 2001
Email: b.h.cuthbertson@abdn.ac.uk
Kill or Update By: September 2004

 

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