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Blood pressure (BP) measurements with an electronic BP device may be affected by excessive movement, such as with seizures, tremors, or shivering, and by irregular heart rates.
BP is the force exerted by blood against the vessel walls. During a normal cardiac cycle, BP reaches a peak, which is 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 at which the BP can sustain the column of mercury.
The most common techniques for measuring BP are auscultation using a sphygmomanometer and stethoscope. 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 1). BP is recorded with the first Korotkoff sound (systolic pressure reading) and 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 (Table 1). 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 underestimate of BP.undefined#ref1">1 Most adults require a large adult cuff, particularly when the cuff is used for a lower extremity BP.1 A bariatric cuff may be needed for larger adults. The thigh BP is not interchangeable with an ankle or upper extremity BP.
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 thigh. Narrow cuffs cause false-high readings.
Rationale: Placing the cuff over clothing may affect the BP measurement.
Rationale: The prone position provides the best access to the popliteal artery. Leg crossing can falsely increase systolic and diastolic BP.
Rationale: Positioning the cuff bladder directly over the popliteal artery ensures that proper pressure is applied during inflation.
Rationale: A loose-fitting cuff causes false-high readings.
Rationale: Looking up or down at the scale can result in incorrect readings.
Rationale: Using the bell of the stethoscope may cause inaccurate reading.
Rationale: Proper stethoscope placement ensures the best sound reception. An improperly positioned stethoscope causes muffled sounds that often result in false-low systolic and false-high diastolic readings. Use of the bell and excessive pressure on the diaphragm of the stethoscope can lead to inaccurate BP measurements.
Rationale: Closing the valve prevents air leak during inflation. Rapid cuff inflation ensures accurate measurement of systolic pressure.
Rationale: Too rapid a decline in the mercury level causes inaccurate readings. Too slow a decline in the mercury level causes discomfort.
Rationale: The first Korotkoff sound is a snapping sound. This sound for at least two consecutive heartbeats reflects the systolic BP.
Rationale: The fifth Korotkoff sound falls silent as the cuff pressure drops below the diastolic pressure. Thus, the beginning of the fifth Korotkoff sound indicates diastolic pressure in adults.
Rationale: Extended cuff inflation causes arterial occlusion, resulting in numbness and tingling in the patient’s leg.
Rationale: Comparing BP in both legs helps detect circulatory problems.
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)
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