Measurement of blood pressure using a digital sphygmomanometer is gaining in popularity because it is considered more practical. However, many clinicians doubt the accuracy of this instrument.

Blood pressure is a component of vital signs. The results of blood pressure measurements affect decisions related to management and medical action. Instruments are used to measure blood pressure include:
a. mercury manometers (mercury manometers),
b. aneroid sphygmomanometers, 
c., and digital sphygmomanometers.

The digital sphygmomanometer is often used in various health centers because it is considered easier to use and does not require specialized expertise in its application.

Application of Digital Sphygmomanometer
Application of Digital Sphygmomanometer

Principle of Digital Sphygmomanometer

Digital sphygmomanometers have an air pump driven by a microprocessor. The microprocessor pumps air automatically into the cuff about 20 mmHg above-average systolic pressure (around 120 mmHg). After the microprocessor captures enough pressure, the knob on the tensimeter automatically loosen, and the air pressure inside the cuff drops slowly.

During the pressing process, an oscillometric wave appears, which is being recorded by the instrument. These oscillometric waves are converted automatically by the device as systolic blood pressure, diastolic blood pressure, pulse pressure, and mean arterial pressure (MAP). The point at which oscillometric waves first appear is read as systolic blood pressure. The point at which oscillometric waves begin to disappear is to be read as diastolic blood pressure.

How to use a digital sphygmomanometer

Appropriate measurement methods and according to the procedure are key to obtaining measurement results as accurately as possible. The following are steps of checking blood pressure using a digital sphygmomanometer:

1. Keep the patient calm and rest the patient from all activities for about 15 minutes before measurement.

2. Use a digital sphygmomanometer that has proven its validity.

3. Position the patient in a lying or sitting condition with the legs not crossed and both feet flat on the floor.

3. Instruct the patient to roll up clothing covering the right arm up to about 2 cm above the elbow line.

4. Make sure the patient's arm is not tangled up with the sleeves of clothes that have been rolled-up before.

5. Attach the cuff to the arm slowly by paying attention to the hose's position, which is parallel to the middle finger of the right arm.

6. After the cuff is positioned correctly, glue the cuff at moderate pressure (neither too loose nor too tight).

7. Position the digital sphygmomanometer as much as possible parallel to the left chest (heart position).

8. Instruct the patient to remain calm during the examination and advise the patient not to talk during the blood pressure measurement process. Ensure that the patient's arm is positioned correctly, and the patient's palm is relaxed and not holding. Also, make sure the blood pressure gauge tube is straight, free from pressure or indentation.

9. Press the "START / STOP" button to activate the blood pressure gauge.

10. Let the blood pressure measuring device carry out the blood pressure measurement process until all the parameters to measure (systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse) is read on the monitor.

11. Take measurements with these steps 2 times, giving a gap between measurements for 2-5 minutes, and make sure the patient's arm is free of the cuff when pausing.

12. Make sure the patient remains relaxed until the next measurement process.

13. If the difference between measurements is more than 10 mmHg, then make the third measurement by giving a 10-minute break from completing the second blood pressure measurement process.

14. Record the measurement results with an average value obtained from all measurements

Digital Sphygmomanometer Accuracy Level

Today, the accuracy of blood pressure measurement results using a digital sphygmomanometer is still controversial. Mercury sphygmomanometer is still the gold standard for measuring blood pressure. However, this instrument also has some disadvantages, such as mercury that is not environmentally friendly, and its use requires special skills. Meanwhile, a digital sphygmomanometer is considered more environmentally friendly and easy to use for all people, including the early community.

At the beginning of its discovery, measuring blood pressure with a digital sphygmomanometer did have a low accuracy level. But over time, the accuracy of the digital sphygmomanometer continues to be improved through a series of validity and reliability tests according to international standard test protocols such as the AAMI (Association for the Advancement of Medical Institution) and the BHS (British Health Society).

A study in 2016 compared the results of blood pressure measurements using aneroid sphygmomanometers and digital sphygmomanometers with results obtained from measurements using mercury sphygmomanometers. The study results showed that digital sphygmomanometers' sensitivity and specificity are indeed lower than those of aneroid sphygmomanometers, which were around 86.7% and 98.7% for aneroid sphygmomanometers and around 80% and 67.7% for digital sphygmomanometers.

Another study in 2018 compared 2 digital blood pressure gauges with different brands to find out whether this digital-based blood pressure gauge had accuracy that was commensurate with the results of blood pressure measurements using a mercury sphygmomanometer. The study results showed that one of the instruments studied gave results that were similar to the results of measurements produced by the mercury sphygmomanometer but not for other devices. Therefore the selection of digital devices used in blood pressure measurement also needs special attention.

Although some studies say the accuracy of blood pressure measurement results with a digital sphygmomanometer is not as high as the mercury sphygmomanometer, other studies suggest that blood pressure measurement results  ​​are not much different from those obtained from a digital sphygmomanometer and mercury sphygmomanometer.

In the end, the selection of blood pressure measuring devices does require consideration from all sides, from the intended use to the user's ability. The study results show that digital sphygmomanometer has a lower accuracy than the mercury sphygmomanometer. Still, in conditions where the purpose of blood pressure measurement is to monitor blood pressure conditions at home or in conditions where the user does not have specialized expertise, this instrument can certainly be considered. It should also be remembered that measuring blood pressure with any noninvasive device requires multiple measurements to get the best and most accurate results.

Source picture:

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