China’s annual death from cardiovascular disease is as high as 17 million people. The awareness rate, treatment rate and control rate of hypertension are all very low, and the control rate in areas with better living conditions is only 30%. In view of this situation, the World Health Organization has called for the introduction of blood pressure monitors into all homes and encouraged patients to self-test their blood pressure. However, the proportion of hypertensive patients in China who self-measure their blood pressure is still very low, taking Shanghai as an example, only 18.7% of hypertensive patients in Shanghai self-measured their blood pressure in 2005. Even for those patients who regularly self-measure their blood pressure, there are many misconceptions. During clinic visits, I often hear hypertensive patients ask many questions, such as “How many times a day is it good to take my blood pressure?” For example, “How many times a day should I take my blood pressure?”, “Which arm should I take?”, “Which arm should I take? What is the best blood pressure monitor to choose? How to take blood pressure accurately? .
Here is a brief overview of how to measure blood pressure correctly and accurately, and its precautions, in the hope that it will be helpful to those who need it.
Assessing blood pressure
Blood pressure measurement is the main tool for diagnosing and evaluating the severity of hypertension. There are direct and indirect methods of measurement.
Direct BP measurement: A catheter is delivered via percutaneous puncture from the peripheral artery to the aorta, and the end of the catheter is connected to a monitoring pressure measurement system that automatically displays the BP value. Although this method is accurate, real-time and not affected by peripheral artery constriction, it is invasive and only suitable for critical and difficult cases.
Indirect measurement method: This is the cuff pressurization method, which is measured by a sphygmomanometer. Sphygmomanometers are available in mercury column, spring type and electronic sphygmomanometers. Mercury column sphygmomanometers or electronic sphygmomanometers tested to international standards (BHS, ESH and AAMI) are commonly used in clinics or hospitals for measurement. Indirect measurement has the advantage of being simple and easy to perform, but is susceptible to a variety of factors, especially changes in peripheral arterial diastole.
Palpation: The subject exposes the upper arm, unfolds the cuff, aligns the middle with the brachial artery, and ties it to the upper arm with a distance of 2 to 3 cm between the lower edge of the cuff and the elbow fossa, with appropriate tightness. One hand palpates the radial artery at the wrist, and the other hand squeezes the leather ball to inflate it rapidly until the radial artery at the wrist cannot be palpated, and then deflates slowly, at which time the pressure decreases, and when the radial artery is palpated for the first time, it is the systolic pressure; however, it should be noted that this method cannot measure diastolic pressure.
The indirect method usually used in clinical practice is the auscultation method, in which the blood pressure value is measured in the brachial artery area of the upper arm. If blood pressure is measured at other sites, this needs to be noted. Because blood pressure is characterized by marked fluctuations, multiple repeated measurements on non-same days are required to determine if the elevation is persistent.
Clinic episodic blood pressure measurement is the current standard method for clinical diagnosis and classification of hypertension and is performed by health care professionals under standard conditions and according to uniform specifications. The specific requirements are as follows.
(1) The person to be measured rests quietly for at least 5 minutes, and smoking and coffee are prohibited for 30 minutes before the measurement, and the bladder is emptied.
(2) The patient should be seated, preferably in a reclining chair, with the right upper arm exposed and the elbow at the same level as the heart. If peripheral vascular disease is suspected, blood pressure should be measured on both arms at the first visit. In special cases, blood pressure can be measured in a lying or standing position. The elderly, diabetic patients and those with frequent postural hypotension should have their blood pressure measured in the standing position. The standing blood pressure should be measured 2 minutes after the prone position is changed to the standing position. The sphygmomanometer should be kept at the same level as the heart regardless of the position of the person being measured.
(3) Use an appropriately sized cuff, with the air bag inside the cuff wrapping at least 80% of the upper arm. Obese people or people with large arm circumference should use a large size cuff, and children should use a smaller cuff.
(4) Tie the cuff to the upper arm of the subject and tighten it so that 1 finger can be inserted. The lower edge of the cuff should be 3 cm above the elbow bend. Place the stethoscope probe in the elbow fossa where the brachial artery pulsates (medial to the transverse elbow), rather than tucking it under the cuff.
(5) It is best to choose a mercury column sphygmomanometer that meets measurement standards for measurement. If you use a mechanical sphygmomanometer or an electronic sphygmomanometer that conforms to international standards, you need to calibrate the value with the mercury column sphygmomanometer at the same time.
(6) When measuring, inflate quickly, the pressure in the balloon should reach the disappearance of the radial artery pulsation and then rise 30 mm Hg (4.0 kPa), then slowly deflate at a constant rate (mercury column decreases 2-3 mm Hg per second. The rate of deflation is slower when the heart rate is slower. Obtain a diastolic blood pressure reading and then deflate quickly to zero.
(7) Listen carefully to the Koch sound during deflation (modified by the Russian Nikolai Kolotkov in 1905? Kolotkov) and observe the vertical height of the convex surface of the mercury column when the first sound is heard, this is the systolic pressure reading; the diastolic pressure reading is taken as the height of the convex surface of the mercury column at the disappearance of the Koch sound (the last sound).
(8) The unit of blood pressure is millimeters of mercury (mmHg). Some official publications will indicate the conversion relationship between mmHg and kilopascal (kPa), 1 mmHg = 0.133 kPa; 1 kPa = 7.5 mmHg.
(9) Measurements should be repeated 2 minutes apart, and the average of the two readings should be recorded. If the difference between the two measured systolic or diastolic readings is >5 mmHg, the measurements should be repeated 2 minutes apart and then the average of the three readings should be taken.
Precautions for measuring blood pressure with a mercury column sphygmomanometer
(1) Regular testing and calibration of the sphygmomanometer is required, and the sphygmomanometer should be inspected before measurement, including whether the glass tube is cracked, whether the mercury is leaking out, whether the pressurized balloon and rubber tube are aging and leaking, and whether the stethoscope is intact.
(2) For those who need to observe blood pressure closely, four determinations should be made: fixed time, fixed location, fixed position, and fixed sphygmomanometer. It helps to determine the accuracy and comparability of the control.
(3) The “0” point of the sphygmomanometer and the arm position (brachial artery) should be at the same level as the heart, i.e., the fourth intercostal space in the sitting position and the mid-axillary line in the lying position. If the brachial artery is higher than the level of the heart, due to the effect of gravity of blood, the measured blood pressure value can be low, the brachial artery is lower than the level of the heart, the measured value is high.
(4) Exclude cuff interference
Air cuff width: The size of the air cuff should fit the patient’s upper arm arm circumference and should wrap at least 80% of the upper arm. If the arm is too large or if the blood pressure is measured in the thigh, the value measured with a standard air cuff will be too high, and conversely, if the arm is too thin or if a child has to take pressure, the result will be low with a standard air cuff. Therefore, in order to ensure accurate measurements in these special cases, an appropriately sized cuff should be used.
If the cuff is too wide, the large blood vessels will be compressed, increasing the resistance to blood flow and causing the beat to disappear before it reaches the lower edge of the cuff, resulting in low values. If the cuff is too narrow, a higher inflation pressure is needed to block the arterial flow, resulting in a high value.
The tightness of the b-wrap cuff should also be appropriate, too tight so that the blood vessels have been pressurized before the injection, so that the measured value is low, too loose so that the rubber bag is spherical, and the effective measurement area is narrowed, so that the measured value is high.
(5) Inflation should not be too violent, too high, so as not to overflow the mercury, affecting the measurement results and patient comfort. If the mercury column bubbles, should be timely adjustment, repair. Deflation should not be too fast, so as not to read the value of the error.
(6) found that the blood pressure inaudible or abnormal, excluding external factors, should be retested. When retesting, drive out the gas in the gas bag, wait for the mercury column to drop to the “0” point, wait a moment (1 ~ 2min) and then measure, avoid continuous pressure, so that the limb circulation is blocked, affecting the measurement value. If necessary, do bilateral control measurements.
(7) When measuring blood pressure for a hemiplegic patient or a patient with trauma to the limb, the healthy limb should be measured to prevent the dynamic changes in the patient’s blood pressure from not being truly reflected due to the obstruction of blood circulation on the affected side.
According to the Korotkoff 5-stage method, the first loud tapping sound (stage 1) represents systolic blood pressure, followed by a weakening of the tapping sound and a soft wind-like murmur as stage 2, and in stage 3 when the pressure is further reduced and the arterial blood flow increases, the tapping sound increases and the murmur disappears. The tone then suddenly becomes dull in phase 4, and finally the sound disappears in phase 5. The blood pressure value in phase 5 is the diastolic blood pressure. In women with pregnancy, severe anemia, hyperthyroidism, aortic valve insufficiency, and Korotkoff sounds that do not disappear, stage 4 can be used as the diastolic blood pressure reading, or diastolic blood pressure can be recorded as both values, e.g., blood pressure 160/80-50 mmHg.