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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 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.
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 arm’s 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 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 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.6 Palpation of BP in the patient’s leg has limited reliability.
Rationale: The urge to void can significantly increase BP.5
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 cuffs can cause an artificially high reading.
Rationale: BP is generally higher in the supine position than in the sitting position.5
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.5
Rationale: Leg crossing can falsely increase systolic and diastolic BP.
Rationale: Leg crossing can artificially increase 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: A loose-fitting cuff can cause an artificially high reading.
Rationale: Looking up or down at the scale can result in distorted, incorrect readings.
If unable to palpate the artery because of a weakened pulse, use an ultrasonic stethoscope.
Rationale: Too rapid or too slow a decline in the mercury level can cause an inaccurate measurement.
Rationale: The estimate of systolic BP determines the maximal inflation point for accurate reading by palpation. Completely deflating the cuff prevents venous congestion and an artificially high reading.
Rationale: Continuous cuff inflation causes arterial occlusion, resulting in numbness and tingling of the arm.
Rationale: Comparison of BP in both arms helps detect cardiovascular, neurologic, and musculoskeletal abnormalities. A difference of more than 10 mm Hg may be clinically significant.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)*
*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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