Palpate the radial or brachial artery pulsation while inflating the cuff to a level of 30 mm Hg above the point at which the brachial or radial artery pulsation disappears. Reinflate the cuff to this pressure and release the pressure (deflate) slowly and steadily at a rate of 2 mmHg/sec. The cuff is deflated fast after the diastolic pressure is recorded. A gap of at least one minute must be given in case the pressure is rerecorded.
What one listens to with the stethoscope are the Korotkoff sounds:
Phase 1 : The first appearance of clear tapping sound. This represents the systolic pressure
Phase 2 : Soft murmurs
Phase 3 : Louder murmurs
Phase 4 : Muffled sounds
Phase 5 : Disappearance of sounds
At what point is the diastolic pressure recorded? Comparative studies with intra arterial measurement shows that it corresponds to Phase 4. However, the diastolic is taken just before disappearance of Phase 5.
What are the conditions where Korotkoff sounds are difficult to hear? In slow rising pulse of aortic stenosis, shock and in heart failure, it might be difficult to hear these sounds. It helps to ask the patient to clench and unclench the fist 5 or 6 times and listen again.
What is the auscultatory gap? This occurs when after the first appearance of the Kortkoff sound, it disappears, then reappears at a lower pressure. For this reason, it is better that the systolic pressure is noted by the palpation of the disappearance of the radial pulse. The cuff pressure must be raised to a point above this before one starts listening to the Korotkoff sounds. When BP is recorded for the first time, it should be done in both arms. A difference of more than 10 mmHg should raise the suspicion of obstructive lesions in the arterial supply to the upper limb.