There are many ways to measure a blood pressure. The most simple and common way to measure a blood pressure is the brachial artery occlusion method, commonly known as ‘the Cuff.’
This is accurate, but the accuracy depends on correct cuff sizing and operator use. It can be done automatically, but once again, training is required for automatic use.
Blood can only be heard through a stethoscope if it is turbulent. As the cuff is inflated, the artery is compressed, making the blood flow through the artery turbulent. When the artery is completely closed, there is no blood flow and no sound. As pressure in the cuff is reduced, the point at which the artery is open just enough to let the blood pass, is the systolic blood pressure.
This is detected by turbulent blood flow heard through the stethoscope. As pressure in the cuff is further reduced, the vessel will once again be completely open and non-turbulent. At this point, no more sound is heard and diastolic blood pressure has been reached.
The arm should be raised slightly, so that it is level with the heart.
It is important to allow the client to rest for a few minutes before measurement of the blood pressure. Any activity will raise the blood pressure slightly, and pain, exertion, stress or heavy exercise may raise it quite a bit.
In regard to the preferred site for measurement, blood pressure may be obtained from different arteries, sometimes from the forearm or leg, but these are not considered as accurate as the brachial arteries as these are closer to the heart.
If there is a blockage in an artery, this will lower the blood pressure. There’s no way to know for sure at the bedside, but if there is a difference between the left and right arms or legs, this would suggest a blockage or stenosis in an artery. In this situation a higher blood pressure would be more accurate.
In truth, the most accurate way to document a patient’s blood pressure is to log the artery tested (especially if it is not the brachial artery), the position of the patient, and any other factor that may have increased or decreased the blood pressure during the measurement, such as pain.