In ARDS, women and short people get higher, potentially deadly tidal volumes - PulmCCM
Dec 312012

In most areas of life, it helps to be tall, and needing treatment for ARDS further proves the rule. Tall people are less likely to get harmful lung-distending tidal volumes during mechanical ventilation, simply by virtue of having bigger lungs. It's bad enough that we intensivists might discriminate against the under-six-feet crowd (of which I am a proud member), but it turns out we aren't very chivalrous, either. In fact, you might say we can be sexist, height-ist brutes.

Seung-Hye Han, Greg Martin, Jonathan Sevransky, et al took a look at mechanical ventilation practices at multiple hospitals over 6 years, and found that intensivists -- who never fail to hold doors for their lady colleagues, or to buy their wives flowers on their anniversaries -- had no qualms at all about dangerously stretching the lungs of women they didn't even know ... and all for the lack of a disposable tape measure.

What They Did

Authors prospectively followed 421 patients with ARDS (about 60% men, 40% women) caused by severe sepsis at 7 academic hospitals, including those at Univ. of Colorado and Johns Hopkins. They checked whether the patients got lung-protective ventilation according to ARDSNet criteria. Notably, patients were on average 40 pounds overweight, as compared to their predicted body weight (using the ARDSNet calculation to determine the proper low tidal volume for mechanical ventilation).

What They Found

Patients only received proper, guideline-compliant low tidal volume mechanical ventilation 53% of the time in the first 2 days after their diagnosis of ARDS.

Women were much less likely to receive lung protective ventilation (46% vs. 59%, p<0.001). It looked as if physicians were probably using actual body weight rather than predicted body weight to calculate tidal volumes, because both men and women received tidal volumes "appropriate" for their actual body weights about 75% of the time.

Most or all the gender difference could be explained by height differences: regressing the data for height, both men and women were 20% more likely to receive appropriate low tidal volumes/lung protective ventilation if they were one inch taller.

What It Means

It's shocking and a little embarrassing that we are only using low tidal volumes -- the one strategy we know improves survival in ARDS --  about half the time. This finding is by no means unusual; in fact, it's been replicated in multiple studies at top academic centers, as we reviewed a couple of weeks ago ("ARDS protocols adherence low at top centers"). Those authors, also from Johns Hopkins, found strong circumstantial evidence that poor adherence by doctors with lung-protective ventilation protocols reduces patients' 2-year survival.

Now it looks like our simple failure to check our patients' heights and use the ARDS predicted body weight calculator probably results in disproportionate harm to our women patients, whose smaller lungs are more vulnerable to our clumsy calculations.

I've got a question. There's a "ventilator setup kit" in every ICU in the developed world. Whether it's a pre-packaged collection of items in a plastic bag, or just a checklist in a respiratory therapist's head, it includes ventilator tubing, humidification, sterile water/saline ampules, bronchodilators, etc., etc.

Why doesn't it include a tape measure???

They cost 17 cents. And you can even get free shipping, if you buy from Dumririch04, online proprietor of Cheap Price Disposable Medical Tape Measures Store, who would also be happy to sell you some Discount Baseball Uniforms Youth.

Kidding aside, I think this is a terribly under-noticed study that just might be giving us a life-saving signal by telling us exactly where we don't "measure up" in treating ARDS, especially for our female patients. Please check it out (it's full free text), and if you agree, spread the word.

Han S, Martin GS, et al. Short Women With Severe Sepsis-Related Acute Lung Injury Receive Lung Protective Ventilation Less Frequently: An Observational Cohort Study. Crit Care; 2011;15 (November 1): R262.

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  5 Responses to “In ARDS, women and short people get higher, potentially deadly tidal volumes”

  1. So is the encouragement to use ARDsNet protocol with ALL patients, or only those in ARDS? I know several physician’s who use it with absolutely everyone and appear to have much better results then those only using it with someone already in ARDS. Any thoughts?

    • Lisa — thanks for writing. There is some good observational evidence that treating all critically ill patients with low tidal volumes is associated with better outcomes. I don’t have the citations handy but hopefully someone will review this topic at some point in the journals. You could ask, is that a real effect or just a marker for having a physician who is more attentive and more current on the guidelines, etc. I would say, what’s the difference? I’d take the low tidal volumes myself. A randomized trial testing this would have to be pretty big to prove anything so don’t expect it soon. Cheers — Matt

  2. Dr. Hoffman,

    I truly like your idea about putting measuring tape with every ventilator setup bag.
    At some institutions we have made a laminated IDBW conversion chart and attached these to every ventilator.
    This has helped with Vt settings for our ALI/ARDS patients, additionally helpful when using ASV.
    Maybe you could trademark the “Hoffman Tape” a tape measure that provides IDBW and lung protective Vt, similar to the “Broselow tape” used in pediatrics?
    Wait, let me take that back maybe I should trademark it.

    • Ha — great idea Scott! I’ll race you to it. Although someone out there has probably already beaten us to it. See you at the patent office…

  3. Tape measures w/ vent setup: DONE.
    In the community hospital where I used to work and at VCU Medical Center where I work now, disposable paper tape measures are with each adult vent setup. We also have a laminated IBW chart hanging on each vent. The challenge: measuring a pt accurately who is in semi-Fowler’s position. We do have discrepencies between resp therapists – working on that now!
    Lois Rowland, MS, RRT-NPS, RPFT, FAARC
    Respiratory Care Education Coordinator
    VCU Medical Center’
    Richmond, VA