Measuring noninvasive blood pressures is an essential procedure in nursing. Measurements can be taken utilizing either a sphygmomanometer or a digitally automated blood pressure cuff. In either case, it is important to ensure the proper size cuff is used and the proper technique is followed. Inaccurate readings can result from either of these scenarios. Equipment should be appropriately calibrated, per policy.
Manual sphygmomanometers come in two types: mercury and aneroid. Mercury is considered the gold standard, however, has become less common due to the potential for mercury exposure in the event of breakage. Aneroid devices utilize a dial that drops commensurately with pressure in the cuff but are at a disadvantage in that they need to be calibrated more often. Both of these devices require the use of a stethoscope. Digital sphygmomanometers use oscillometric measurements, and do not require a stethoscope.
Cuff size must be appropriate to the patient. If a cuff is too small, a blood pressure reading may be falsely elevated. Likewise, if a blood pressure cuff is too large, a blood pressure reading may be falsely low. The patient should be seated comfortably having rested for at least five minutes prior to measuring the blood pressure. Ensure that the arm used does not have a limb alert, or contraindication for blood pressure measurement, such as for the presence of lymphedema or a dialysis fistula. The blood pressure cuff artery indicator should be centered over the brachial artery. Ensure that the cuff fits snuggly but is not overly tight or loose.
If utilizing a digital sphygmomanometer, press the start button. If using a manual sphygmomanometer, it is important to establish the target pressure for cuff inflation. Palpate the radial artery with the fingers of one hand while rapidly inflating the cuff until the pulse disappears and add 30 mmHg to this number to determine the target pressure. Place a stethoscope diaphragm or bell over the brachial artery and inflate the cuff rapidly to the target pressure. Note the level when you hear faint Korotkoff sounds that increase in intensity for two beats. This measurement is a systolic blood pressure. As the cuff deflates, the sounds will soften and then disappear. This measurement is the diastolic blood pressure.
To better ensure accuracy, the blood pressure should be repeated after a one-minute wait period. The two readings should be averaged and recorded as the blood pressure
- Normal blood pressure is considered a systolic blood pressure less than 120 mmHg and diastolic blood pressure less than 80 mmHg.
- Using the appropriate size cuff is crucial in accurate blood pressure measurement.
- Variability in technique can lead to inaccurate readings.
Bickley, L. S., Szilagyi, P. G., Hoffman, R. M., & Soriano, R. P. (2021). Bate’s Guide to Physical Examination and History Taking (13th ed.). Wolters Kluwer Health: Philadelphia.