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If unable to palpate an artery because of a weakened pulse, use an ultrasonic stethoscope (Figure 1).
Blood pressure (BP) is the force exerted by blood against the vessel walls. During a normal cardiac cycle, BP reaches a peak, followed by a trough. The peak pressure occurs when the heart's ventricular contraction, or systole, forces blood under high pressure into the aorta. When the ventricles relax, the blood remaining in the arteries exerts a trough, or diastolic, pressure against the arterial wall. Diastolic pressure is the minimal pressure exerted against the arterial wall at all times.
The standard unit for measuring BP is millimeters of mercury (mm Hg). The measurement indicates the height to which the BP can sustain the column of mercury.
The most common methods for measuring BP are auscultation using a sphygmomanometer and a stethoscope and measurement using an electronic BP monitor. Palpation may be used to obtain an estimate of systolic BP before using the auscultation method.
During auscultation, as the sphygmomanometer cuff is deflated, five different sounds, called Korotkoff sounds, are heard over the artery. Each sound has a distinct characteristic (Figure 2). BP is recorded with the systolic reading (first Korotkoff sound) before the diastolic reading (beginning of the fifth Korotkoff sound). The difference between systolic pressure and diastolic pressure is the pulse pressure. For a BP of 120/80 mm Hg, the pulse pressure is 40 mm Hg, the difference between 120 mm Hg and 80 mm Hg.
Cuff size should be proportionate to the limb circumference. Most adults require a large adult cuff. An improper-size cuff produces inaccurate BP measurements. Studies show that using a cuff that is too narrow results in an overestimation of BP and using a cuff that is too wide results in an underestimation of BP.undefined#ref1">1
When measuring BP in the upper arm is not possible—for example, when the available BP cuffs do not fit the upper arm properly—BP may be measured in the forearm. To obtain the most accurate reading, the nurse must use the proper size BP cuff for the forearm, which typically has a smaller circumference than the upper arm. BP measurements in the forearm and upper arm are not interchangeable. Forearm measurements tend to be higher than upper-arm measurements with the greater variability in systolic BPs.6 The thigh or calf can be used if measurement of the upper arms and forearms is not possible.1
Rationale: The urge to void can significantly increase BP.
Rationale: Exposure to cold can significantly increase systolic BP.
Rationale: Proper cuff size is necessary for an accurate reading. The cuff must be wide and long enough to allow for the size of the arm or thigh. Narrow cuffs cause false-high readings.
Rationale: BP is generally higher in the supine position than the sitting position.
Rationale: If the patient's arm is not supported at the heart level, a lower BP will be recorded when the arm is above heart level, and a higher BP will be recorded when the arm is below heart level.
1 Leg crossing can falsely increase systolic and diastolic BP.
Rationale: Leg crossing can falsely increase systolic and diastolic BP.
Rationale: The prone position provides the best access to the popliteal artery. Leg crossing can falsely increase systolic and diastolic BP.
Rationale: Leg crossing can result in a false reading of increased systolic and diastolic BP.
Rationale: Placing the cuff over clothing may affect the BP measurement.
Rationale: Positioning the cuff bladder directly over the brachial artery ensures that proper pressure is applied during inflation.
Rationale: A loose-fitting cuff causes false-high readings.
Rationale: Positioning the cuff bladder directly over the radial artery ensures that proper pressure is applied during inflation.
Rationale: Positioning the cuff bladder directly over the popliteal artery ensures that proper pressure is applied during inflation.
Rationale: Looking up or down at the scale can result in distorted incorrect readings.
Rationale: Too rapid or slow a decline in the mercury level causes inaccurate readings.
Rationale: The estimate of systolic BP determines the maximal inflation point for accurate reading by palpation. Completely deflating the cuff prevents venous congestion and false-high readings.
If unable to palpate the artery because of a weakened pulse, use an ultrasonic stethoscope.
Rationale: Continuous cuff inflation causes arterial occlusion, resulting in numbness and tingling of the arm or leg.
Rationale: Comparison of BP in both arms or legs helps detect cardiovascular, neurologic, and musculoskeletal abnormalities. A normal difference of up to 10 mm Hg may exist between arms.
Daskalopoulou, S.S. and others. (2015). The 2015 Canadian hypertension education program recommendations for blood pressure measurement, diagnosis, assessment of risk, prevention, and treatment of hypertension. Canadian Journal of Cardiology, 31(5), 549-568. doi:10.1016/j.cjca.2015.02.016 (Level I)
*In these skills, a “classic” reference is a widely cited, standard work of established excellence that significantly affects current practice and may also represent the foundational research for practice.
Adapted from Perry, A.G., Potter, P.A., Ostendorf, W.R. (Eds.). (2018). Clinical nursing skills & techniques (9th ed.). St. Louis: Elsevier.
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