Therapy Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome
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Summary
Posted By:	Gordon S. Doig
E-Mail:	Gordon.Doig@EvidenceBased.net
Posted Date:	20 July 2001
Title:	Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome
Authors:	The Acute Respiratory Distress Syndrome Network
Reference:	N Engl J Med 2000;342:1301-8
Link:	Click here for a direct link to the paper. A password may be required for access to fulltext.
Abstract:	BACKGROUND: Traditional approaches to mechanical ventilation use tidal volumes of 10 to 15 ml per kilogram of body weight and may cause stretch-induced lung injury in patients with acute lung injury and the acute respiratory distress syndrome. We therefore conducted a trial to determine whether ventilation with lower tidal volumes would improve the clinical outcomes in these patients. METHODS: Patients with acute lung injury and the acute respiratory distress syndrome were enrolled in a multicenter, randomized trial. The trial compared traditional ventilation treatment, which involved an initial tidal volume of 12 ml per kilogram of predicted body weight and an airway pressure measured after a 0.5-second pause at the end of inspiration (plateau pressure) of 50 cm of water or less, with ventilation with a lower tidal volume, which involved an initial tidal volume of 6 ml per kilogram of predicted body weight and a plateau pressure of 30 cm of water or less. The primary outcomes were death before a patient was discharged home and was breathing without assistance and the number of days without ventilator use from day 1 to day 28. RESULTS: The trial was stopped after the enrollment of 861 patients because mortality was lower in the group treated with lower tidal volumes than in the group treated with traditional tidal volumes (31.0 percent vs. 39.8 percent, P=0.007), and the number of days without ventilator use during the first 28 days after randomization was greater in this group (mean [+/-SD], 12+/-11 vs. 10+/-11; P=0.007). The mean tidal volumes on days 1 to 3 were 6.2+/-0.8 and 11.8+/-0.8 ml per kilogram of predicted body weight (P<0.001), respectively, and the mean plateau pressures were 25+/-6 and 33+/-8 cm of water (P<0.001), respectively. CONCLUSIONS: In patients with acute lung injury and the acute respiratory distress syndrome, mechanical ventilation with a lower tidal volume than is traditionally used results in decreased mortality and increases the number of days without ventilator use.
Are the Results Valid?
1. Was the assignment of patients to treatments randomized? ( Was allocation concealment maintained?)
	Yes. A centralized interactive voice system was used for randomization.
2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?
2a. Was followup complete?
	The primary outcome was death before discharge from hospital. All patients were followed-up until hospital discharge.
2b. Were patients analyzed in the groups to which they were randomized?
	The study was analyzed on an intention to treat analysis and all patients were analyzed in the groups to which they were randomized to
3. Were patients, health workers, and study personnel blind to treatment?
	No. Since this was a trial comparing two ventilation protocols, it would be impossible to blind.
4. Were the groups similar at the start of the trial?
	Table 2 demonstrates that both groups were similar with respect to all measured factors except baseline minute ventilation. The baseline minute ventilation was significantly higher (13.4 vs. 12.7 liters/min, p=0.01) in the group treated with lower tidal volume.
5. Aside from the experimental intervention, were the groups treated equally?
	There were no differences with regards to use of neuromuscular blocking agents or sedatives between the two groups. Use of inotropes, PA catheters, antibiotics etc is not explicitly reported.
What are the Results?
1. How large was the treatment effect?
	Mortality was significantly lower in the group treated with lower tidal volumes (31% vs. 39.8%, p=0.007).
2. How precise was the estimate of the treatment effect?
	The absolute mortality reduction was 8.7% with a 95% confidence interval from 2% to 15%. This would suggest that if you were to implement this protocol in your hospital, you would have a 95% chance of observing a benefit anywhere from as small as 2% to as large as 15%.
Will the Results Help Me In Caring For My Patients?
1. Can the results be applied to my patient care?
	Yes. The protocol is explained quite well and can be implemented with any ventilator with assist control.
2. Were all clinically important outcomes considered?
	Mortality, duration of ventilation and ventilator free days are reported. Duration of ICU and hospital stay are not clearly emphasized. Quality of life after hospital discharge (long term follow-up) is not reported.
3. Are the likely treatment benefits worth the potential harms and costs?
	Unless there is a huge increase in duration of stay, which is unlikely since duration of ventilation was similar in both gorups, the benefits of ventilation with the ARDS net protocol far outweigh the costs or potential harms.
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