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If unable to palpate an artery because of a weak pulse, use an ultrasonic stethoscope (Figure 1).
Blood pressure (BP) measurements with an electronic BP device may be affected by excessive movement, such as with seizures, tremors, or shivering and irregular heart rates.
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 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 at which the BP can sustain the column of mercury.
The most common techniques for measuring BP are auscultation, using a sphygmomanometer and 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 extremity circumference (Table 1). Most adults require a large adult cuff. An improper-size cuff produces an inaccurate BP measurement (Table 2). Studies show that 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
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, a proper size BP cuff for the forearm should be used; it typically has a smaller circumference than the upper arm. BP measurements in the forearm and upper arm are not interchangeable. Systolic blood pressure readings tend to be higher in more distal arteries, such as those in the forearm, and diastolic blood pressure readings tend to be lower in the more distal arteries.7,8 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.6
Rationale: Exposure to cold can significantly increase systolic BP.6
Rationale: 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.1
Rationale: The prone position provides the best access to the popliteal artery. Leg crossing can falsely increase systolic and diastolic BP.
Rationale: Placing the cuff over clothing may affect the BP measurement.
Rationale: Positioning the cuff bladder directly over the popliteal artery ensures that proper pressure is applied during inflation.
Rationale: A loose-fitting cuff can cause an artificially high reading.
Rationale: Looking up or down at the scale can result in incorrect readings.
Rationale: Using the bell of the stethoscope may cause an inaccurate measurement.6
Rationale: Proper stethoscope placement ensures the best sound reception. An improperly positioned stethoscope can cause muffled sounds that can result in an artificially low systolic and an artificially high diastolic reading. Use of the bell and excessive pressure on the diaphragm of the stethoscope can lead to inaccurate BP measurements.6
Rationale: Closing the valve prevents air leak during inflation. Rapid cuff inflation ensures accurate measurement of systolic pressure.
Rationale: Too rapid or too slow a decline in the mercury level can cause an inaccurate measurement.
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.6 The fourth Korotkoff sound involves distinct muffling of sounds and indicates diastolic pressure in children.9
Rationale: Continuous cuff inflation causes arterial occlusion, resulting in numbness and tingling of the patient’s leg.
Rationale: Comparison of BP in both legs helps detect cardiovascular, neurologic, and musculoskeletal abnormalities. A normal difference of up to 10 mm Hg may exist between legs.1
Rationale: The prone position provides the best access to the popliteal artery. Leg crossing can artificially increase BP.
Rationale: A loose-fitting cuff causes false-high readings (Table 2).
Rationale: Pressing the cancel button immediately deflates the cuff.
A patient with abnormal bleeding tendencies is at risk for microvascular rupture from repeated inflations.
Rationale: Comparing BP in both legs helps detect circulatory problems.
American Heart Association (AHA). (2017). What is high blood pressure? Retrieved April 8, 2021, from https://www.heart.org/en/health-topics/high-blood-pressure/the-facts-about-high-blood-pressure/what-is-high-blood-pressure (Level VII)
*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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