Method of blood pressure measurement
The indirect arterial blood pressure measurement (“NIBP”, non-invasive bloog pressure), is a procedure which is used daily in the medical routine. A blood pressure cuff is applied to one limb, usually the arm, and then the blood pressure is measured using a monitor or stethoscope. Although the measurement in this way is not as accurate as the direct method, the method is harmless, faster and does not involve any risks.
With indirect measurement, a distinction is made between manual and automatic blood pressure measurement. Manual blood pressure measurement can be performed auscultatorily, palpatorily and oscillatorily. In the auscultatory method, the blood pressure cuff is placed around the upper arm and inflated by hand.
A stethoscope is then placed on the crook of the arm and the pressure in the cuff is slowly reduced. As soon as the arterial pressure in the vessel exceeds the pressure of the cuff, a flow noise can be heard during auscultation. This is called the Korotkow sound and represents the value of the systolic pressure.
The pressure in the cuff is released further until the cuff pressure falls below the pressure in the vascular system. At this moment the flow noise stops, this value corresponds to the diastolic blood pressure. Also with the palpatory method, a blood pressure cuff is applied to the upper arm.
By releasing the pressure and simultaneously palpating the radial pulse on the wrist, the systolic pressure can be determined. This pressure is generated when the pressure in the vascular system exceeds the pressure of the cuff and the pulse can be felt on the wrist for the first time. The diastolic value cannot be determined in this way.
For this reason, the palpatory method is the method of choice for orienting measurement in noisy environments, for example in rescue services. Oscillatory blood pressure measurement is performed in the same way as the other two measurement methods, but the blood pressure values are estimated on the basis of a pulse-synchronous pointer deflection on the measuring device. The manual method of this procedure is very inaccurate.
However, automatic blood pressure machines, for example in the recovery room, also measure the pressure using this method. As an alternative to the invasive method, the pressure is measured continuously at intervals of a few minutes. Long-term blood pressure measurement is also carried out using the same principle.
Here, the patient wears a blood pressure cuff for 24 hours, which inflates itself at certain intervals, measures the blood pressure automatically and stores the values in a recording device. In this way, the blood pressure course of a whole day can be evaluated later and any high blood pressure can be detected and assessed. With all these procedures, the measurement must be taken at heart level.
This must be taken into account especially with measuring devices on the wrist. Furthermore, the blood pressure cuff must be the right size for the upper arm, otherwise false high or false low values can be measured. Direct blood pressure measurement (“IBP”, “invasive blood pressure”), is an invasive method for measuring arterial pressure.
A peripheral artery, usually the arteria radialis or femoralis, is punctured from the outside. Then a small catheter is inserted into the artery, which is equipped with a pressure sensor. This sensor registers the arterial blood pressure curve and displays it on a monitor.
The advantage of this method is a continuous monitoring of the blood pressure as well as a simultaneous measurement of the heart rate and the mean arterial pressure. Since the method is invasive, it is associated with the risk of bleeding, infection and nerve injury. For this reason, direct blood pressure measurement is not a routine procedure, but is mainly performed by anaesthetists in an intensive care unit or during operations.
Indications for this invasive method are patients at vital risk and major surgical interventions on the heart, vascular system, liver, brain or thorax. Just as in the arterial system, blood pressure can also be measured directly in the venous system. The upper vena cava (superior vena cava) is punctured and the central venous pressure is measured there. Since a right-heart catheter examination is performed as part of this measurement, the pressure in the pulmonary circulation and other areas of the right heart can then be measured simultaneously.
