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Effects of a Clinical Trial on Mechanical Ventilation Practices in Patients with Acute Lung Injury

¹ Division of Pulmonary and Critical Care, School of Medicine, The Johns Hopkins University, Baltimore, Maryland; and ² Pulmonary and Critical Care Unit, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts

Correspondence and requests for reprints should be addressed to William Checkley, M.D., Ph.D., Division of Pulmonary and Critical Care, The Johns Hopkins University, Baltimore, MD 21205. E-mail: wcheckl1{at}jhmi.edu

Rationale: In a clinical trial by the Acute Respiratory Distress Syndrome Network (ARDSNet), mechanical ventilation with tidal volumes of 6 ml/kg decreased mortality from acute lung injury. However, interpretations of these results generated controversy and it was unclear if this trial would change usual-care practices.

Objectives: First, to determine if clinical practices at ARDSNet hospitals changed after the tidal volume trial. Second, to determine if tidal volume and plateau pressure (Pplat) within 48 hours before randomization affected hospital mortality in patients subsequently managed with 6 ml/kg predicted body weight (PBW).

Methods: We used preenrollment data from 2,451 patients enrolled in six trials (1996–2005) to describe changes in tidal volume over time. We used logistic regression to determine if preenrollment tidal volume or Pplat affected mortality.

Measurements and Main Results: Median preenrollment tidal volume decreased from 10.3 ml/kg PBW (range, 4.3–17.1) during the tidal volume trial (1996–1999) to 7.3 ml/kg PBW (range, 3.9–16.2) after its completion (P < 0.001). Preenrollment tidal volume was not associated with mortality (P = 0.566). The odds of death increased multiplicatively with each cm H₂O of preenrollment Pplat (P < 0.001) (e.g., the odds of death was 1.37 times greater when preenrollment Pplat increased by 10 cm H₂O).

Conclusions: Physicians used lower tidal volumes after publication of the tidal volume trial. Preenrollment Pplat was strongly associated with mortality, and may reflect disease severity independent of tidal volume. Pplat measured early in the course of acute lung injury, after accounting for tidal volume, is a respiratory system–specific value with strong prognostic significance.

Key Words: acute lung injury • mechanical ventilation • clinician practices

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject In an ARDS Network clinical trial, mechanical ventilation with low tidal volumes decreased mortality from acute lung injury. Interpretations of these results generated controversy, and it was unclear if this trial would change clinical practice. What This Study Adds to the Field Substantial reduction in usual-care tidal volumes occurred at ARDS Network hospitals after the trial. Plateau pressure early in the course of acute lung injury, accounting for tidal volume, is a respiratory system–specific value that predicts mortality.