Back to basics: When a blood pressure isn’t always a blood pressure

The care we deliver leans heavily on vital signs. You have more than a handful of data points making up the umbrella term “vital signs” that contribute to hemodynamic stability, but today I want to talk about blood pressure.

A blood pressure is one of those objective measurements that can reveal so much about the status of a patient’s health. It not only gives a statement of their current status, but can reveal subtle clues about their previous or impending condition.

With all of this in mind, we really should be experts at the actual measurement, but the practice of measuring blood pressure has sadly become a thing of the past. We rely almost completely on the machines to do it, and rarely question their accuracy.

I thought I’d point out just a few things that can alter a blood pressure measurement. Keep all of them in mind when your patient’s blood pressure becomes unstable or abnormal.

Common mistakes:

Position of patient

• The ideal position is the patient sitting upright with their feet supported for at least 15 minutes. Any change in position will affect the blood flow to the extremity.

Position of arm

• It should be relaxed at their side. They should not have their arm extended out in front of their torso, nor should they be clenching or tensing their arm.

Time of day

• Diurnal blood pressure variation means a patient’s blood pressure should be lower in the early morning as well as in the late evening. A 10-20% change in both systolic and diastolic can be normal!

Size of cuff

• For some reason, everyone forgets this one. An improperly sized cuff will give a falsely high or low measurement. Be sure the cuff securely fits around their upper arm while allowing 1-2 finger widths under the cuff.

Location of cuff on arm

• This one aggravates me. Be sure your abnormal cuff reading isn’t due to the cuff being around the patient’s elbow!! It should be above the insertion of the biceps tendon, not over the anticubital area.

Here are a few honorable mentions:

Repeated cuff measurements 

• Frequent vital sign checks will affect a patient’s “normal” blood pressure range. Continual repeated measurements in a short time frame can cause falsely elevated measurements due to muscular and vascular spasming.

Choice of pulse location

• This has more to do with variation. The further away the actual anatomical measurement is from the heart, the lower the blood pressure will be. An ankle BP will be lower than a radial BP which will be lower than an upper arm BP. It’s simple physiology.

Location of stethoscope bell

• If you fancy doing a manual blood pressure measurement, be sure the bell of your stethoscope is not under the BP cuff. Also, keep the pressure of your finger on the back of the bell constant, because it will cause the Korotkoff sound to falsely disappear too quickly.

Body habitus

• Last but not least, subcutaneous fat can give false readings. It may read falsely high due to improper cuff fit, or read falsely low due to inaccurate pulse recognition. Many situations require invasive monitoring for accurate measurement.

One unstable or abnormal blood pressure measurement does not make an unstable patient. Be sure to monitor the trend over a set amount of time before making clinical decisions based on a singular piece of objective data.

Be safe out there.