Expansion
Cuff size, position, rate of deflation and repetition
Expansion
Technique
- Patient seated and rested for 5 minutes, back supported, legs uncrossed, not talking
- Arm supported at heart level; an unsupported or dependent arm raises the reading
- Cuff bladder encircling 80 per cent of the arm circumference and covering two thirds of its length
- Palpate the radial pulse and inflate 20 to 30 mmHg above its disappearance, to avoid missing an auscultatory gap
- Deflate at 2 to 3 mmHg per second
- Korotkoff I is systolic, Korotkoff V (disappearance) is diastolic
- Measure in both arms at first assessment; a difference over 15 mmHg is significant and suggests subclavian stenosis or dissection. Use the higher arm thereafter
- Repeat and take the lower of two readings if they differ by more than 10 mmHg
Sources of error
| Error | Effect |
|---|---|
| Cuff too small | Overestimates |
| Cuff too large | Underestimates |
| Arm below heart level | Overestimates |
| Rapid deflation | Underestimates systolic |
| Auscultatory gap | Underestimates systolic |
| Talking, cold, full bladder, recent caffeine | Overestimates |
Postural blood pressure: measure supine after 5 minutes, then at 1 and 3 minutes standing. A fall of 20 mmHg systolic or 10 mmHg diastolic, or symptoms, defines postural hypotension.
Automated devices are unreliable in atrial fibrillation, in preeclampsia and at the extremes of pressure, where manual auscultation is required.
Confirm hypertension with ambulatory or home monitoring, since white coat hypertension is common and treatment is lifelong.