Noninvasive blood pressures

When I am attending, I use non-invasive blood pressure (NIBP) monitoring all the time.  I have my own adult automatic cuff that I bring to work.  I find it to be practical on long transports and on patients where I need serial blood pressures.

Dr Pierre Potain's sphygmomanometer, circa 1870
Credit Wellcome images, via Wikimedia Commons

I find, though, that most other medics despise automated blood pressures.  I am most often told that the blood pressures of NIBP cuffs are unfailingly incorrect.  I have always thought this was both funny and the perfect description of a paramedic’s mindset: "All of the rest of medical practice is wrong, except for how I do it."  Think about it – NIBP readings are used in doctors’ offices, emergency departments, operating rooms, and hospitals all over the world.  Do you think that nobody checked to see if these things worked? 

To me, the biggest benefit to using NIBP is that it frees me up to undertake other tasks.  If there are no other tasks, it frees up my brain to think about the call.  Contemplating the call (what else could be going on, what I may be missing, what else I could be doing, and those types of things) is the most significant task on a call. 

Some of the best overview information comes from two nursing documents.  The first was a 2002 article in the journal Critical Care Nurse.¹ Apparently nurses had the same concerns that medics continue to have: “Despite the widespread use of automated blood pressure monitors, clinicians continue to deliberate over the accuracy and reliability of automated NIBP devices compared to other methods of blood pressure determination.”  The article cites nine studies that support NIBP accuracy, within 5mmHg of direct arterial pressure measurements.  The article states, however, that there can be occasional random NIBP pressures that vary from the arterial pressure by more than 30mmHg and cautions clinicians against making treatment decisions off of a single NIBP reading.

The Emergency Nurses Association wrote a clinical practice guideline regarding noninvasive blood pressure measurement in 2012.² This document works through pertinent research to reach three main recommendations: Compare NIBP readings to auscultated BPs, use the right sized cuff, and follow manufacturers’ guidelines.  More specifically, they find that NIBP measurement is suitable for adult patients, patients with trauma and shock, and children.  Evidence for NIBP use is weaker in the case of patients with chronic hypertension, atrial fibrillation, pregnancy, and alternative cuff sites. 

So if you are finding that the auto cuff is returning readings that are grossly different from your auscultated readings on a consistent basis, the cuff may not be the problem.  But, like any tool, automated BP cuffs have limitations.  They are usually a bit slower than I am.  They can be confused by arm movement or flexing against the inflated cuff.  Reported variations between auscultated blood pressures and automated blood pressures range from +5.4 to -11.2 mmHg in systolic blood pressures.  You need the right cuff for the patient.  They can occasionally fire off a wildly wrong reading.  Finally, I have a suspicion that NIBP readings have more variation at the extremes of systolic pressures. 

Auscultated blood pressures have limitations, as well.  Blood pressures take two hands and one brain.  No studies have established the range of variation between measured arterial pressure and the auscultated pressure reported by the new firefighter who inflated the cuff four times and has a look on his face like he is translating calculus to French in his head.  Like with NIBPs, you need the right cuff to fit the patient.  Finally, auscultated blood pressures have no automatic setting to result in a blood pressure reading every three minutes (or 10 minutes or 30 minutes…).

Thus, like with any tool, procedure, or medication, I need to balance the positives and negatives of NIBP readings against the pros and cons of manual blood pressures.  When I am tending to most patients, I check a manual blood pressure first.  After all, it is pretty quick and simple in most cases.  If I have a patient that is likely to need another blood pressure reading, I use the NIBP cuff.  Because arm movement can screw with the blood pressure reading, the patient needs to be able to hold still and not flex against the cuff.  So they need to be unresponsive or able to follow directions.  The NIBP cuff needs to give a reading that is in the same ballpark as what I got with the manual cuff.  If all that is true, I can set up the cycle time for something appropriate and get back to other work.

Don’t completely ignore the NIBP cuff.  It can be a pretty helpful tool.

1. Dobbin KR. Noninvasive blood pressure monitoring. Crit Care Nurse 2002;22(2): 123-4.

2. Emergency Nurses Association 2012 Resources Development Committee. Clinical Practice Guideline: Non-invasive blood pressure measurement with automated devices. December 2012.  Accessed January 15, 2015 http://www.ena.org/practice-research/research/CPG/Documents/NIBPMCPG.pdf