Blood Pressure: Measurement Techniques, Cuff Sizes & Normal Values

Basic Principle: Occluding the artery of an extremity (arm/leg) with an inflatable cuff to measure pressure either oscillometrically or by detection of Korotkoff sounds.

Prerequisites

1. Appropriate Cuff Size

• Bladder should cover the circumference without overlapping.
• Width: Should cover 2/3rds the distance between axilla and cubital fossa.

Age Group	Cuff Width (approx)
Neonate	3 cm
Infant	5 cm
Young Children	7 cm
Older Child/Adolescent	12.5 cm

2. Subject Preparation

• Relaxation: 5 mins rest before first reading. No talking.
• Position: Comfortably seated, legs uncrossed.
• Level: Mid-point of cuff on upper arm at level of Right Atrium (mid-sternum).
• Clothing: Remove all clothing from the area.
• Bias Control: Take at least 2 readings, 2 mins apart. Same observer if possible.

Measurement Techniques

1. Auscultatory Method (Gold Standard)

1. Fit cuff snugly. Place stethoscope just under the edge (cubital fossa).
2. Inflate while palpating radial artery until pulse disappears, then go 20-30 mmHg higher.
3. Deflate slowly.
4. Systolic BP: First "blrrpp" or tapping sound (Korotkoff Phase I).
5. Diastolic BP: Disappearance of sound.

2. Palpatory Method

• Palpate pulse while deflating.
• Level where pulse returns = Systolic BP.
• Note: Cannot measure Diastolic BP.

3. Flush Method

• Useful in infants/young children.
• Step A: Raise limb vertically, wrap cuff, hold till palm becomes pale.
• Step B: Inflate cuff, lower arm, deflate slowly.
• Reading: The point where the palm turns PINK again = Systolic BP.

4. Automated (Oscillometric)

• Detects oscillations in cuff pressure.
• Displays Systolic, Diastolic, Mean BP, and Heart Rate.

Normal Values

Neonate Age	Systolic (Mean)	Diastolic
Term Neonate	~ Gestational Age	-
1 month - 1 year	80 mmHg	55 mmHg
1 year - 5 years	85 mmHg	60 mmHg

Note: A child is hypertensive if BP exceeds the 95th centile for age/sex. Boys generally > Girls.