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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. 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 minimum pressure exerted against the arterial wall.
Patients at risk for alterations in BP measurement include those who have:
The standard unit for measuring BP is millimeters of mercury (mm Hg). The measurement indicates the height to which 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, or if unable to obtain a BP by auscultation.
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 1). BP is recorded with the first Korotkoff sound (systolic pressure reading) at the beginning of the fifth Korotkoff sound (diastolic pressure reading). 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 can produce an inaccurate BP measurement. Using a cuff that is too narrow results in an overestimation of BP, whereas using a cuff that is too wide results in an underestimation of BP.undefined#ref1">1,6
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 proper-size BP cuff must be used for the forearm, which typically has a smaller circumference than the upper arm. BP measurements in the forearm and upper arm are not interchangeable. Systolic BP readings tend to be higher in more distal arteries, such as those in the forearm, whereas diastolic BP readings tend to be lower in the more distal arteries.5 The thigh or calf can be used if measurement of the upper arms and forearms is not possible.5 A bariatric cuff may be needed for larger adults. Thigh BP is not interchangeable with an ankle or upper extremity BP.
Rationale: Exposure to cold can significantly increase systolic BP.5
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 cuff can cause an artificially high reading.
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 the heart level.5 Leg crossing can 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.
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 can cause an artificially high reading.
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 a decline in the mercury level causes an inaccurate measurement. Too slow a decline in the mercury level causes discomfort.
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.
Rationale: Continuous cuff inflation can cause 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.6
American Heart Association (AHA). (2016). What is high blood pressure? Retrieved June 6, 2022, from https://www.heart.org/en/health-topics/high-blood-pressure/the-facts-about-high-blood-pressure/what-is-high-blood-pressure (classic reference)*
Shimbo, D. and others. (2020). Self-measured blood pressure monitoring at home: A joint policy statement from the American Heart Association and the American Medical Association. Circulation, 142(4), e42-e63. doi:10.1161/CIR.0000000000000803 Retrieved June 6, 2022, from https://www.ahajournals.org/doi/10.1161/CIR.0000000000000803
*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.
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