Blood Pressure: Lower Extremity - CE
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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 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. Systolic BP readings tend to be higher in more distal arteries, whereas diastolic BP readings tend to be lower in more distal arteries.undefined#ref4">4,5 The thigh or lower calf/ankle is used if measurement of the upper arms and forearms is not possible.8 Ankle blood pressure is clinically effective in diagnosing hypertension when the upper arm is not available for proper cuff placement.7
Cuff size should be proportionate to the limb circumference (Table 1). An improperly sized cuff produces 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.4 Most adults require a large adult cuff, particularly when the cuff is used for taking BP in a lower extremity.4 A bariatric cuff may be needed for larger adults. The correct cuff size is especially important for obtaining accurate readings in pediatric patients and patients with obesity.5
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Rationale: A full bladder increases pressure on the kidneys and can increase blood pressure.
Rationale: Exposure to cold can increase systolic BP.4
Rationale: An improperly sized cuff produces inaccurate BP measurements.
Rationale: The prone position provides the best access to the popliteal artery. Leg crossing can 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 an incorrect reading.
Rationale: Proper stethoscope placement ensures the best sound reception. An improperly positioned stethoscope causes muffled sounds that often result in an artificially low systolic and an artificially high diastolic reading.
Rationale: Closing the valve prevents air leak during inflation. Rapid cuff inflation ensures accurate measurement of systolic pressure.
Rationale: Too rapid or slow a decline in the mercury level can cause inaccurate measurements.
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.4
Rationale: Continuous cuff inflation causes arterial occlusion, resulting in numbness and tingling of the patient’s leg.
Rationale: Comparing BP in both legs helps detect circulatory problems.
Rationale: The prone position provides the best access to the popliteal artery. Leg crossing can increase BP.
Rationale: Pressing the cancel button immediately deflates the cuff.
Patients with abnormal bleeding tendencies are at risk for microvascular rupture from repeated inflations.
*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. and others (Eds.). (2022). Clinical nursing skills and techniques (10th ed.). St. Louis: Elsevier.
Clinical Review: Martha Beck, MA, BSN, RN, CNOR
Published: August 2023
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