Dec 312012
(image: Wikipedia)

Anyone with the keys to a ventilator knows, or should, that low tidal volume ventilation (~6 mL/kg ideal body weight) for patients with ARDS can be lifesaving: as many as one in 11 people with ARDS treated by low tidal volume ventilation may have their lives saved or extended while in the hospital.

Low tidal volume ventilation is considered standard care for ARDS, but as with any “standard” care implemented by flawed human beings and our systems, it is not perfectly practiced, 100% of the time. But what about at top academic institutions?

What They Did

Dale Needham, Elizabeth Colantuoni, Peter Pronovost, Roy Brower et al prospectively followed 485 patients with ARDS at Johns Hopkins and University of Maryland hospitals, obtaining their recorded ventilator settings twice daily (a total of 6,240 vent settings or 8 per patient). Investigators followed the patients for two years after diagnosis, comparing their survival according to how consistently they were treated with low tidal volume ventilation. They published their results in the April 5, 2012 BMJ.

What They Found

Only 41% of the observed ventilator settings were compliant with low tidal volume ventilation guidelines for ARDS. And a somewhat surprising 37% of patients were never treated with low tidal volume ventilation (at least according to the collected ventilator settings).

It mattered! The degree to which a patient's physicians and care team adhered to low tidal volume ventilation practice directly correlated with that patient's chances for survival at two years:

  • 311 (64%) of the 485 ARDS patients died at two years overall.
  • Each additional measured ventilator setting adherent with low tidal volume guidelines for ARDS reduced the risk of mortality at two years by a relative 3% (P=0.002).
  • Each additional 1 mL/kg in tidal volume imposed on a patient with ARDS carried an 18% relative increase in mortality risk at 2 years.
  • Compared to ARDS patients treated with a mean 6.5 mL/kg tidal volume, those treated with 6.5 - 8.5 mL/kg had a hazard ratio for death at 2 years of 1.59; those treated with >8.5 mL/kg had a hazard ratio for death of 1.97.

Authors estimated that (compared with no adherence to low tidal volumes) a patient treated with 50% adherence with low tidal volumes for ARDS would experience a 4% absolute risk reduction in mortality at two years; a patient treated with 100% adherence with low tidal volumes would experience an 8% absolute risk reduction in mortality.

What It Means

Why only a 40% adherence with low tidal volume ventilation for ARDS at a top U.S. academic medical center? The exasperated authors simply refer you to their earlier work showing knowledge deficits and culture barriers, prevalent erroneous physician beliefs about supposed contraindications or just failing to diagnose ARDS, and forgetting to do it because no ICU protocol was in place. In fact, these adherence rates represent a significant improvement over the last go-round of examining LTVV adherence soon after the ARDSNet trial (although that was a while ago).

I'll throw in the obligatory this was a single-center observational trial, correlation does not prove causation, etc. But here you have an intervention previously proven to improve survival, now with a robust linear (inverse) relationship between adherence with that intervention and observed mortality ... it's hard to demand more than this from research of this type.

Like other work from these authors, this article is a humbling and compelling reminder of how valuable the discipline of "health services research" might become. Health services research studies real-world care systems, with one of its goals ensuring all patients gain the benefits of therapies proven in randomized trials. They say it like this:

Rigorous knowledge translation research, aimed at improving the implementation of clinical research into practice, is needed to maximise the public’s return on investment from clinical and preclinical research that established the short term efficacy of lung protective ventilation.

In our “don't ask, don't look, don't tell” paranoid medical culture ever-fearful of lawsuits, bad press and the Quality Police, credit is due here for the confidence and courage to self-examine and report on their own practice and performance. Any areas for improvement found at Johns Hopkins are overwhelmingly likely to be present at most other community and academic medical centers. Before saying "We don't have that problem here," I'd ask: How would you know? 

Needham DM et al. Lung protective mechanical ventilation and two year survival in patients with acute lung injury: prospective cohort study. BMJ 2012;344:e2124.

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Adherence with low tidal volumes for ARDS is poor at top centers; reduces survival