As a student nurse on placement in a busy ED, I recall taking a blood pressure measurement on a patient and rushing off to the primary care nurse – “the patient is really hypotensive!”. The experienced RN glanced at the patient and merely said, “you have to do it again on the lower arm”. Bewildered, I returned to the patient and obediently shifted the cuff down the patient’s arm towards the wrist…. resulting in some odd looks from other staff. Now I know – of course – that he meant I should take the BP on the arm that was level with the patient’s heart.
Meanwhile, I have blithely performed lying and standing BP measurements on patients with suspected orthostatic hypotension – you know, the (usually elderly) patients who present with pre-syncope, light-headedness, or increased falls. I usually try to do the standing blood pressure quickly, while the patient sways on their feet and I stretch to reach the “start” button on the BP machine without letting them slip through my grasp. My goal? To get them back into bed as quickly and safely as possible.
However, I recently noticed that one of the RNs at work was doing the standing BP after letting the patient stand for a minute. No-one had ever told me to do that, so I went searching and sure enough… an accurate standing BP should be taken after the patient has been standing for 2-5 minutes. Not satisfied with this, I continued my search, because when I change my practice I like to know why.
Usually, when you stand up, about 500-1000mL of blood pools in your lower legs. The body responds by increasing venous return to the heart, resulting in a small fall in systolic blood pressure (5 to 10 mmHg). When autonomic reflexes are impaired, blood pressure falls progressively after standing because the pooling of blood in the legs cannot be compensated by sympathetic vasoconstriction. Orthostatic hypotension is diagnosed when, within two to five minutes of quiet standing (after a five minute period of supine rest), one or more of the following is present:
- at least a 20 mmHg fall in systolic pressure
- at least a 10 mmHg fall in diastolic pressure
- symptoms of cerebral hypoperfusion.
So there you have it. A personal practice-changer. Lots more fascinating information can be found in the article “Mechanisms, causes, and evaluation of orthostatic and postprandial hypotension” by Kaufmann, H, Mann, NM, and Freeman, R. (Last updated August 1, 2012).