How do you measure blood pressure (BP) from the leg?

How to Measure Blood Pressure from the Leg

To measure blood pressure from the leg, use a thigh cuff or an appropriately sized larger cuff placed on the thigh, with auscultation over the popliteal fossa to detect Korotkoff sounds. 1

Proper Technique for Leg BP Measurement

Equipment and Positioning

• Cuff selection: Use a thigh cuff or an appropriately sized larger cuff that is suitable for the circumference of the thigh 1
• Patient position: The patient should be in a comfortable position, typically supine
• Placement: Position the cuff on the thigh with the bladder centered over the posterior surface
• Auscultation site: Place the stethoscope over the popliteal fossa (behind the knee) 1

Measurement Procedure

1. Allow the patient to rest for 3-5 minutes before measurement
2. Initially inflate the cuff while palpating the popliteal pulse to estimate systolic pressure
3. Inflate the cuff to 30 mmHg above the estimated systolic pressure
4. Deflate the cuff at a rate of 2-3 mmHg per second
5. Record systolic pressure at the first Korotkoff sound and diastolic pressure at the fifth Korotkoff sound
6. Take at least two measurements and average the results 1

Clinical Significance and Interpretation

Normal Values and Interpretation

• In the general population, ankle systolic BP is typically 17 mmHg higher than arm systolic BP 2
• For diastolic BP, there is generally no significant difference between arm and ankle measurements (-0.3 mmHg) 2
• Important: In patients with vascular disease, ankle systolic BP may be significantly lower than arm BP (by approximately 33 mmHg) 2

Clinical Applications

• Screening for coarctation of the aorta: Children with elevated BP on repeated arm measurements should have BP measured in the leg; if leg systolic BP is >10 mmHg lower than arm systolic BP, additional studies for coarctation should be performed 1
• Assessment in patients with peripheral arterial disease: When ABI (ankle-brachial index) is >1.40 but PAD is clinically suspected, toe-brachial index or other imaging should be used 1
• Alternative measurement site: When BP cannot be measured in the arms due to bilateral injuries, surgeries, or vascular access devices

Common Pitfalls and Considerations

• Cuff size errors: Using a cuff that is too small will significantly overestimate blood pressure; ensure proper cuff size for the thigh circumference 1
• Positioning errors: Ensure the patient is properly positioned with adequate support and the leg at heart level when possible
• Interpretation errors: Remember that normal leg BP values differ from arm values; do not apply the same diagnostic thresholds 2
• Vascular disease: In patients with peripheral arterial disease, leg BP measurements may be falsely low 1
• Measurement sequence: When measuring both arm and leg BP, follow a systematic sequence: first arm, first PT artery, first DP artery, other PT artery, other DP artery, and other arm 1

Special Populations

Children

• In children, use an appropriately sized cuff based on the child's thigh circumference
• For older children, a 9×18 cm cuff may be appropriate; for larger children, use a standard adult cuff, large adult cuff, or thigh cuff as needed 1
• Ensure the child is comfortable and relaxed during measurement to minimize anxiety-related BP elevation

Patients with Vascular Disease

• In patients with suspected peripheral arterial disease, ankle BP may be significantly lower than arm BP 2
• When ABI is abnormal (either <0.90 or >1.40), additional testing is warranted 1
• For patients with occlusive arterial disease in all four limbs, alternative methods for BP assessment may be necessary 1

By following these guidelines, clinicians can obtain accurate leg blood pressure measurements that contribute to proper diagnosis and management of various cardiovascular conditions, particularly in situations where arm measurements are not feasible or when screening for specific vascular disorders.