Lung-Protective Ventilation Saves Lives, But We Don’t Use It
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, is Editor for Critical Care Alert.
Synopsis: Even at an ARDSNet-participating academic medical center and well after publication of that study’s findings that low-tidal-volume ventilation saved lives, only a minority of patients with acute lung injury were receiving tidal volumes of 7.5 mL/kg predicted body weight or less.
Source: Kalhan R, et al. Underuse of lung protective ventilation: analysis of potential factors to explain physician behavior. Crit Care Med. 2006;34:300-306.
Kalhan and colleagues at the hospital of the University of Pennsylvania (a participating ARDSNet investigation site) performed a prospective observational cohort study of patients with acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS) managed in their ICUs during a 22-month period beginning after publication of the initial ARDSNet study.1 The investigators determined the proportion of patients for whom tidal volume on days 2, 4, and 7 of ALI/ARDS was 7.5 mL/kg predicted body weight (PBW) or less (as used in 95% of the patients in the low-tidal-volume group in the original ARDSNet study). In a sensitivity analysis, they also determined how many patients were receiving not more than 6.5 mL/kg PBW and 8.5 mL/kg PBW at those same times.
Of 175 patients with ALI/ARDS screened during the study period, half were excluded for a priori reasons, so that the study population comprised 88 patients. These 88 patients were ventilated with an assortment of modes, per the managing teams: 25% with volume assist-control, 31% with volume intermittent mandatory ventilation, 33% with pressure support, and 11% with pressure control. However, only 39% of them were on tidal volumes not more than 7.5 mL/kg PBW by the end of the second day after ALI/ARDS diagnostic criteria were met. The proportions on day 4 and day 7 were 49% and 56%, respectively. About half of all patients with ALI/ARDS (49%) were receiving tidal volumes exceeding 8.5 mL/kg PBW on day 2, 30% on day 4, and 24% on day 7. Patients with lower arterial PO2 values and lower values for total respiratory system static compliance tended to be on low tidal volumes more often. Thus, this study demonstrates that, even at a participating ARDSNet study hospital, physicians managing patients with ALI/ARDS used lung-protective ventilation in only a minority of instances.
Commentary
The number needed to treat in the original ARDSNet low-tidal-volume study1 was 11. This means that for every 11 patients managed with tidal volumes of 6 mL/kg instead of 12 mL/kg PBW in that study, one life was saved. There has been a great deal of debate about the design of that study, with some people claiming that 12 mL/kg was a tidal volume no longer used in actual patient management, rendering the findings irrelevant, and others providing evidence that, in fact, tidal volumes in that range are still very commonly used, especially when tied to PBW rather than to actual body weight. The fact is that there are few interventions in critical care that have been demonstrated so convincingly to save lives as simply using lower tidal volumes and end-inspiratory plateau pressures during mechanical ventilation. And yet several studies have shown that even at participating ARDSNet centers, where the staff certainly ought to know how to perform it, lung-protective ventilation is not in fact used in managing most patients with ALI/ARDS. Why not? At these same institutions, therapies whose benefits are supported by far less compelling evidence have been put into wide usage.
This study is not the first to show a low rate of use of lung-protective ventilation. The accompanying editorial by Young2 lists several others, including studies from other ARDSNet centers, that have demonstrated similar findings. Measuring height in order to calculate PBW is still not done in many ICUs, and in the ARDSNet study1 actual body weight was on average 20% greater than PBW. Studies have shown that, despite internationally standardized criteria, ALI/ARDS remains a grossly underdiagnosed condition. A survey of ICU nurses and respiratory therapists by Rubenfeld et al3 found that physicians were often concerned about patient discomfort from low-tidal-volume ventilation, and also frequently felt that this management approach was medically contraindicated for their patients. In addition, lung-protective ventilation is a form of protocolized patient management, a concept still resisted by some despite bountiful evidence that it improves care.
Whether a tidal volume of 6 mL/kg PBW and an end-inspiratory plateau pressure less than 30 cm H2O are optimally lung-protective are unproven to the satisfaction of some, and are likely to remain so for awhile. However, given the findings of the ARDSNet study1 and others4 that low tidal volumes and distending pressures improve outcomes, the onus in 2006 is on any clinician who does not manage ALI/ARDS patients this way to demonstrate otherwise. Unawareness of current standards, and failure to recognize ALI/ARDS when it is present in one’s patients, is hard to defend when lives are at stake.
References
- The Acute Respiratory Distress Syndrome Network: Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342:1301-1308.
- Young M. Tidal volumes used in acute lung injury: Why the persistent gap between intended and actual clinical behavior? Crit Care Med. 2006;34:543-544.
- Rubenfeld GD, et al. Barriers to providing lung-protective ventilation to patients with acute lung injury. Crit Care Med. 2004;32:1289-1293.
- Amato MBP, et al. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med. 1998;338:347-354.
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