-33-
methodologies, such as the Korotkoff Sound Method and oscillating method. The Korotkoff Sound
Method is used as a conventional way, whereby stethoscope is used to measure the blood
pressure. By the oscillating method, an inflation pump will fill the air, and release it slowly. A
computer will record change of the cuff pressure when the air is released. With this record, the
blood pressure value will be determined. First of all, make sure the signal quality judgment by
computer meets the requirements of accurate calculation (such as sudden limb movement or cuff
being hit during the measurement). If the answer is negative, give up the calculation. If the answer
is positive, proceed with calculation of the blood pressure value.
As change of the blood pressure is recorded by electric sensor, which sensitivity is much higher
than that of human ears, the oscillating method uses different definitions for measurement of
diastolic pressure, mean arterial pressure and systolic pressure from the Korotkoff Sound Method.
When the oscillating method is used, the circuit in the measuring apparatus will separate the
amplitude of the cuff pressure from its change with pulsation. With the oscillating method, the
blood pressure at the maximum amplitude of cuff pressure is defined as the mean arterial
pressure. The blood pressure at amplitude of cuff pressure forward reduced according to proper
proportion is defined as systolic pressure, while the blood pressure at amplitude of cuff pressure
backward reduced according to proper proportion is defined as diastolic pressure. The maximum
change of pulse pressure occurs at these two points. They are equivalent to the point with pulse
sound and the point without pulse sound respectively in the Korotkoff Sound Method.
When the risk of invasive monitoring method outweighs its advantage of accuracy, non-invasive
monitoring method shall be used.
7.2.1 Points to be noted in NIBP Measurement
Like common non-invasive blood pressure measurement, improper operation may cause
inaccurate or blank result or misunderstanding of the measuring information when the oscillating
method is used to take the measure of blood pressure. This point needs particular attention of the
operators.
1. Requirements of the cuff:
1) Appropriate cuff should be selected according to the age of the subject.
2) Remember to empty the residual air in the cuff before the measurement is commenced.
3) Locate the cuff in such a way that the “” mark is at a location where the clearest pulsation
of brachial artery is observed.
4) The cuff should be tightened to a degree where insertion of one finger is allowed.
5) The lower end of the cuff should be 2cm above the elbow joint.
2. The subject should lie on the back so that the cuff and the heart are in a horizontal position
and the most accurate measure is taken. Other postures may lead to inaccurate
measurement.
3. Do not speak or move before or during the measurement. Care should be taken so that the
cuff will not be hit or touched by other objects.