What is noninvasive blood pressure (NIBP)？

author: Myra

2023-09-28

The measurement method of NIBP

The NIBP measurement method of multi-parameter monitor is generally the oscillation method, and its principle is as follows: The cuff tied to the arm is used to inflate the cuff with an air pump to block the propagation of the pulse in the blood vessel. When the pressure reaches a certain level (generally 124~316kPa), the blood flow can pass through the blood vessel, and there are certain oscillating waves, which gradually deflate and the oscillating waves become larger and larger. As the contact between the cuff and the arm becomes looser and looser, the pressure and fluctuations detected by the pressure sensor become smaller and smaller, and the pressure sensor can detect the pressure and fluctuations in the cuff in real time. We assume that the moment of maximum fluctuation is selected as the reference point, and based on this point, the fluctuation point of peak 0.45 is found forward. This point is the high pressure (i.e., the systolic pressure), looking back is the fluctuation point of the peak 0.75, which corresponds to the low pressure (i.e., the diastolic pressure), and the point with the highest fluctuation corresponds to the average pressure.

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Advantages and disadvantages of NIBP

1.Advantages

Non-invasive, good repeatability；
Easy to operate, easy to master；
Wide adaptability, suitable for all ages, sizes of surgery, hypertension patients；
Automatic blood pressure monitoring, timed pressure measurement on demand, saving time and effort.

2.Disadvantages

It cannot be continuously monitored, it cannot reflect the blood pressure of each cardiac cycle, and it cannot display the arterial waveform;
Peripheral vascular constriction at low temperature, hypovolemia, and hypotension affected the measurement results;
The interval time of pressure measurement is too short, the time of pressure measurement is too long, and the upper limb nerve ischemia and numbness occur.

Factors affecting the correct measurement of NIBP

1.Arm clothing thickness
Studies have shown that the systolic and diastolic blood pressure values measured by every layer of clothing with a thickness of less than 0.5cm are significantly higher than those measured by standard methods, with an average difference of 12.5 mmHg in systolic blood pressure and 8.3mmHg in diastolic blood pressure.

2.The selection standard of the cuff
Cuff width is another important factor affecting the accuracy of non-invasive blood pressure monitoring. Patients with different arm girth should use different armbands to measure blood pressure. This is determined by the principle of non-invasive blood pressure monitoring.

3.Differences in blood pressure measurements of different postures
The study found that there was no statistically significant difference between the blood pressure of the ipsilateral upper limb in the lateral position and that of the horizontal upper limb, while the blood pressure of the opposite upper limb was lower than that of the horizontal position, with statistically significant difference.

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