Friday, June 18, 2010

BP Measurement (mercury column sphygmomanometer)


The key to the reservoir should be turned open
The mercury meniscus should be at zero
The calibrated glass tube must be clean – a dirty tube can cause inaccurate readings.


The bladder length should encircle at least 80% of the circumference.
The width should be at least 40% of the circumference of the arm.
Too small a cuff will give a falsely higher reading and vice versa.


The following may indicate malfunction of the device:
# Failure to achieve a pressure of 40 mmHg above the estimated SBP or 200 mmHg after 3–5 seconds of rapid inflation.
# The inability of the equipment to deflate smoothly at a rate of 1 mmHg per second or at each pulse beat.


Patients should be adequately rested and seated with their arms supported.

The cuff and the mercury reservoir should be at the level of the heart.

They should not have smoked or ingested caffeine within 30 minutes of measurement.

The SBP should be estimated initially by palpation. While palpating the brachial/ radial artery, the cuff is inflated until the pulse disappears. The cuff should then be inflated to a further 20 mmHg. The cuff is then slowly deflated and the pressure at which the pulse is palpable is the estimated SBP.

The bladder is again inflated to 20 mmHg above the previously estimated SBP and the pressure reduced at 1-2 mmHg per second whilst auscultating with the bell of the stethoscope.
The bell should not be placed under the cuff.

The point at which repetitive, clear tapping sounds first appears (Korotkoff Phase I) gives the SBP.

Phase I sounds sometimes disappear as pressure is reduced and reappears again at a lower reading (the auscultatory gap), resulting in underestimation of the SBP.

The complete disappearance of sound (Korotkoff Phase V) should be taken as the diastolic reading.

In some groups, e.g. anaemic or elderly patients, the sounds may continue until the zero point. In such instances the muffling of the repetitive sounds (Korotkoff Phase IV) is taken as the diastolic pressure. The point of muffling is usually higher than the true arterial diastolic pressure. If Korotkoff Phase IV is used, this should be clearly recorded.

BP should be measured in both arms and the higher reading is taken as the systemic BP.
If the difference in BP between the two arms is >20/10 mmHg, there may be an arterial anomaly which requires further evaluation.


The BP should be taken both lying and at least one minute after standing to detect any postural drop, especially in the elderly and in diabetics. On rising, the BP will transiently rise and then fall. A systolic drop of >20 mmHg is considered a significant postural drop.

source : Ministry Of Health Malaysia

learning issue : what is Korotkoff Phase?



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