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 will 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. To be sure, many patients with ARDS who are not optimally treated with lung protective ventilation will survive. But for how long?
What They Did
Dale Needham, Elizabeth Colantuoni, Peter Pronovost, Roy Brower et al prospectively followed 485 patients with ARDS at Johns Hopkins and U. 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 … if you want more than that, you’re a tough cookie (or just an unrealistic one).
Like other work from these authors, this article is a humbling and compelling reminder of how badly we need their nascent, still-finding-its-way discipline of “health services research,” which means studying and working to improve real-world care to ensure 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.
Let’s give credit to these institutions and their people who are confident and dedicated enough to examine and report on their own processes and performance, in our “don’t ask, don’t look, don’t tell” paranoid medical culture ever-fearful of lawsuits, bad press and the Quality Police. Any “flaws” they find in the care at Johns Hopkins are overwhelmingly likely to be present at many, if not most other community and academic medical centers, I suspect. Before saying “We don’t have that here,” I’d ask: How do you know?
Maybe it’s better for our egos, and the status quo, that they published this one in the British Medical Journal, no?
Clinical Takeaway: Ask not for whom the ventilator alarm bell tolls: it tolls for thee.
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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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
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.