Adherence with low tidal volumes for ARDS is poor at top centers; reduces survival - PulmCCM
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Dec 312012
 
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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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  5 Responses to “Adherence with low tidal volumes for ARDS is poor at top centers; reduces survival”

  1. This is an Interesting article in which the results were shocking, especially coming from Johns Hopkins.
    Johns Hopkins is well known for their adherence to the low tidal strategy for ARDS.

    I’m glad that the authors mentioned “failing to diagnose ARDS” may attribute to the low compliancy.
    I cannot recall the last time the intensivist during ICU rounds inquired about the patients current PaO2/Fio2 ratio, ask if there have been any acute changes in FiO2 requirements, and coupled this with a chest radiograph reading of bilateral infiltrates consistent with pulmonary edema.

    From my experience this seems to be an issue with the facility. The facility/institution is so focused on ventilator length of stay that we focus primarily on the liberation phase of mechanical ventilation.
    We are very good with wean indices and wean protocols, and should extend these types of assessments to lung protection protocols.

    Daily or BID screening of ventilator patients using systems already in place examples; ARDS/ALS definitions or “Murray Score” [1].
    1. Murray, et al. Am Rev Respir Dis 138 (1988), 720-723

  2. Obviously my response is only theoretical, but my concern is actually with the protocols. At academic centers, too often residents are taught about the theory and evidence for low tidal volume ventilation, but then have the vent management taken out of their hands and put into the hands of the RT’s, using protocols. In clinical trials, where protocols are followed rigorously and compliance with protocols frequently assessed, turning over vent settings to a protocol (like the ARDS PEEP ladder, for example), likely improves outcomes. Outside of studies I wonder whether turning over vent management to RT’s doesn’t cause some harm, in their lack of compliance with the actual protocol and no one ever checking the RT’s work.

    The other issue, which is silly but true, is that I rarely see tape measures in the ICU, and patients who need to be on ventilators cannot tell you their height. Instead, I see people go off of weight (rather than IBW) all the time. Given the average BMI in the US is close to 30, it’s not surprising that people are on too high of volumes.

  3. I would be curious if they also looked at PEEP and FiO2. Adherence to the ARDSnet strategy requires both a Low Tidal Volume lung protective strategy and following their PEEP/FiO2 scale. It seems that many physicians choose to follow the 6 ml/Kg strategy, but choosing to ignore the rest of the protocol.

    • Brian: The PEEP / FiO2 in the rest of the ARDS protocol are much more flexible as I understand them — because higher and lower PEEPs have been compared in subsequent RCTs without detection of a definite benefit / harm from either. That said, a subgroup analysis (reader beware of these in general) did show a benefit of higher PEEP in the sickest (most hypoxemic) patients with ARDS — see the ventilator induced lung injury review December 2013 on this blog. So, sounds like you and I will both be using the “FiO2-PEEP ladder” from the ARDS protocol you describe. Thanks for writing! -matt

  4. […] Adherence with low tidal volumes for ARDS is poor at top centers; reduces survival (BMJ) — 6 mL/kg tidal volumes saves lives. This paper suggests the way we translate life-saving research into clinical practice needs to improve. […]

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