Blood Pressure Measurement - Complete Guide for MBBS Interns

Fig. 288-2 from Harrison's Principles of Internal Medicine 22E (2025) - Key elements for accurate office BP measurement

Equipment Required

• Sphygmomanometer - cuff with inflatable bladder, inflating bulb, controlled exhaust valve, and manometer (mercury, aneroid, or digital)
• Stethoscope (bell end preferred)
• Properly sized cuff

• Bladder width = at least 40-50% of arm circumference at midpoint
• Bladder length = 80% of midarm circumference (or twice the width)
• Using too small a cuff gives falsely HIGH readings; too large gives falsely LOW readings

STEP-BY-STEP PROCEDURE

STEP 1 - Patient Preparation (30 minutes before)

• Ask patient to avoid caffeine, smoking, alcohol, and exercise for 30 min
• Ensure the patient has an empty bladder (full bladder raises BP by ~10-15 mmHg)
• Bring the patient into a quiet room with comfortable ambient temperature
• Let the patient rest for 3-5 minutes before the first reading
• No talking or cell phone use during the rest period or measurements

STEP 2 - Positioning the Patient

• Patient seated in a chair with upright back support
• Feet flat on the floor (crossing legs raises BP)
• The measurement arm bare and comfortably supported on a surface
• Mid-arm (cuff) must be at the level of the heart (right atrium)
• If the arm hangs freely parallel to the body, readings will be 9-14 mmHg higher than true value

STEP 3 - Applying the Cuff

• Expose the bare upper arm (no clothing bunched underneath)
• Place the cuff 2-3 cm (approximately 2.5 cm) above the antecubital fossa (elbow crease)
• The center of the inflatable bladder should be placed directly over the brachial artery
• The artery marker on the cuff (if present) should align with the brachial artery
• Wrap the cuff snugly - you should be able to fit 2 fingers underneath, not more

STEP 4 - Estimate Systolic BP by Palpation First (Riva-Rocci technique)

• Palpate the radial pulse with 2 fingers
• Inflate the cuff while palpating the radial artery
• Note the pressure at which the radial pulse disappears - this is the estimated systolic BP
• Inflate 30 mmHg above this level for the auscultatory measurement
• Deflate fully and wait 30-60 seconds before re-inflating for auscultation

STEP 5 - Auscultatory Measurement (Standard Method)

• Place the bell of the stethoscope (or diaphragm) lightly over the brachial artery in the cubital fossa - do NOT tuck it under the cuff
• Reinflate the cuff to 30 mmHg above the estimated systolic (from Step 4)
• Open the deflation valve and deflate slowly at 2-3 mmHg per second (or per beat)
• Listen carefully for Korotkoff sounds

Korotkoff Sounds - What to Listen For

Korotkoff phases - Roberts and Hedges' Clinical Procedures in Emergency Medicine

In adults: Record Korotkoff Phase I as systolic, Phase V as diastolic. In children and pregnant women: Use Phase IV as diastolic.

STEP 6 - Recording and Reporting

• Record the exact mmHg readings - do not round up or down excessively
• Report as systolic/diastolic (e.g., 120/80 mmHg)
• Note which arm was used, patient position (sitting/lying/standing), and time
• Inform the patient of the result

STEP 7 - Repeat Measurements

• Take at least 2 readings separated by at least 1-2 minutes in the same sitting
• Use the average of the two readings
• If readings differ by >5 mmHg, take a third and average all three
• On the first visit, measure BP in both arms - use the arm with the higher reading subsequently
• An inter-arm difference of >15 mmHg systolic is clinically significant (consider subclavian stenosis)

BP Classification (ACC/AHA 2017)

Common Errors to Avoid

Special Situations You May Encounter in Internship