Sunday, October 23, 2011

EMS Blood Pressures Aren't Unreliable

Ever since a trauma patient billed as normotensive with stable vital signs rolled off the elevator with CPR in progress having "just lost pulses", I've been somewhat skeptical of my prehospital report, including vital signs.  This study, at least, supports a position that, barring untruthfulness, EMS providers vital signs are usually not clinically significantly different than vital signs obtained on arrival to the Emergency Department - even if observed techniques for EMS providers weren't perfect.

The first phase study looked at 100 patients arriving in the Emergency Department.  BP measurements were obtained within 5 minutes of arrival, and compared to the reported measurement from EMS.  There was approximately a 17mmHg +/- spread to the systolic pressures measured by EMS compared to the first BP in the Emergency Department.

The second phase of the study had observers riding with EMS and documenting the technique at which they used to find vital signs - and then having the research assistants performing the same measurement in the field as well.    In this phase, EMS providers systolic pressure was only a 10.1mmgHg +/- spread away from the research assistant - despite having ideal technique deficiencies and a terminal digit preference for numbers ending in zero.

The article concludes that EMS providers measurements had poor agreement with subsequent measurements, and that the differences were clinically significant.  However, based on the distribution of error in their Bland-Altman plots, I disagree that assessment, as most of the variability occurred throughout a range of inconsequential systolic pressures between 120 and 170.  They unfortunately had very few patients with clinically important hypo- or hypertension, so the question really remains unanswered whether EMS measurements at the clinically important extremes are reliable.

I do find it rather entertaining that their methods included a "specially trained research assistant" to measure blood pressure, referred to in the title as an "expert".  You can be an "expert" in anything nowadays, apparently.

"Agreement between emergency medical services and expert blood pressure measurements."
www.ncbi.nlm.nih.gov/pubmed/21982624

7 comments:

  1. It's not surprising, accurately hearing BPs over the diesel is sometimes an exercise in futility. Also, many providers I precept auscultate far too quickly to hear anything more accurate than a number ending in 0. Lazy plays a large roll in the other inaccuracies I see (not to mention inappropriate cuff sizes).

    We've gone to auto-cuffs for repeat vitals while transporting, but they are awfully inaccurate when the truck is bouncing/swaying. I like them when I have a stable patient, otherwise I'm not a fan.

    Stronger medical direction could help in terms of provider quality/education, but ultimately you may have to live with it...

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  2. What an unusual study. My first reaction is...how did they get so many medics NOT to use their automated blood pressure cuff? :) And my second...what was the agreement with the researcher's blood pressure reading with the Emergency Department staff?!

    "AHA criteria for BP measurement" is a little amusing because if you read the actual paper - from 1988 I might add - they provide instructions on how to use mercury sphygs. How vintage! A glaring technique difference that the researchers SHOULD have asked/observed in either part of the study is whether or not the arm was at the level of the heart.

    This study could have been modified to have the researchers listen through a dual-headed stethoscope to see if there was agreement in number accuracy during systolic/diastolic between researcher and medic...

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  3. There are lots of ways the study could have been done slightly differently, but I think the end result would probably be about the same conclusions - EMS blood pressures could be better, but they're generally not off in a clinically significant way. And, considering the operating constraints, that's pretty good.

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  4. First I wonder why we’re always getting picked on. When was the last time anyone tried to measure the accuracy of an emergency department BP? Second I wonder when the last time an emergency department relied on anything but a machine to take a blood pressure for most patients? Sure, there’s the rare instance of someone breaking out a Doppler, but that’s RARE, I haven’t seen it in years. How many times have you brought a patient in that you KNOW is hypotensive just to see the ED machine say otherwise, and everyone in the room buys it? Nobody bothers to reach over to the wall and actually take it for real. We all know that OUR machine acquired BP isn’t accurate all the time, why should we expect the ED’s to be? Then I wonder how the research assistants were trained. How much experience did they have outside the sterile atmosphere of the hospital? Take a hospital worker out of the confines of their institution, no matter what the training, tech, RN, MD and put them in the field and they’re generally like a fish out of water. It’s a completely different dynamic. We need to start standing up for ourselves. Maybe we should go in set up a study, and evaluate the accuracy of hospital blood pressures; but I’m betting that wouldn’t be allowed!

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  5. I love any efforts to research EMS skills and interventions, but this study doesn't really answer the "So what?" response. That is to say, Does it really matter if the BP is reported in deciles?

    As the guy answering the radio, I want to hear if the BP is low, sky-high, or somewhere in the middle. Is the SBP 150 or 180? I don't care! It's more than 90, less than 290...

    Now, under 90 mmHg, I start caring, but I assume that the medics are also getting a lot more careful with their technique when they start getting pressures in that area. Otherwise, I want them spending their attention and care doing stuff that actually matters, like serial ECGs!

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  6. Hey, I just dug up the Singer and Hollander paper from '96, where they took simultaneous upper arm BPs in the ED.

    http://www.ncbi.nlm.nih.gov/pubmed/8823153

    About 20% of patients had a difference of 20 points in either the SBP or DBP.

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