1.7: Blood Pressure Measurement

Blood pressure is a vital sign obtained routinely in hospital and outpatient settings. The term blood pressure describes the lateral pressure produced by blood upon vessel walls. One of the most important applications of blood pressure measurement is the checking for increased blood pressure, a condition termed hypertension.

This video will illustrate the principles behind traditional blood pressure measurement technique and then it will review the critical steps to be followed during this procedure.

The equipment needed for traditional, indirect measurement of blood pressure includes a stethoscope and a sphygmomanometer. The sphygmomanometer consists of a blood pressure cuff containing a distensible bladder, a rubber bulb with an adjustable valve, which, when closed, helps in cuff inflation and, when open, releases the built-up pressure. It also consists of tubing - connecting the cuff to the bulb, and to the manometer, which displays the cuff's pressure in mmHg.

In order to record the blood pressure reading, the examiner wraps the cuffs around the brachial artery, places a stethoscope over this artery, inflates the cuff above the expected systolic pressure and then deflates it while auscultating and observing the manometer simultaneously.

Initially, when the cuff is fully inflated, the artery is squeezed and the blood flow is halted. Thus, there is no sound upon auscultation. Upon deflation, the first appearance of the Korotkoff sounds signifies the systolic pressure, which is audible due to the turbulent blood flow in the partially squeezed artery. Further deflation causes a continual decrease in cuff pressure, and the Korotkoff sounds remain audible throughout, up until the point when the cuff pressure is below the minimal arterial pressure. This reading denotes the diastolic pressure. The fraction of systolic over diastolic is recorded as the final blood pressure reading.

With this knowledge, now let's go through the step-by-step procedure of obtaining accurate blood pressure readings. If necessary, provide the patient with a gown and ensure that he or she is rested for at least 5 minutes prior to obtaining the measurement. To guarantee an accurate reading, ensure that the patient is sitting comfortably with their feet uncrossed and resting on the floor. The cuff should be placed about 2.5 cm above the antecubital fossa. Confirm proper sizing by looking at the index line on the cuff when wrapped around the arm; it should fall within the marked arm circumference range limits. This is critical, as a smaller cuff may falsely elevate the readings and potentially lead to misdiagnosis. Also, make sure that the patient's arm is resting with the brachial artery at the level of the heart. This is also important because if the arm is below the heart level, it may lead to an overestimation, and if it is above, it might result in an underestimation of systolic and diastolic pressures.

Next, find the radial pulse with your index finger. Once the pulse is identified, close the valve on the pressure bulb by turning it clockwise. Then, inflate the cuff by squeezing the pressure bulb rapidly. Continue doing this until the radial pulse cannot be felt anymore, and note the pressure reading on the manometer. Inflate further until the pressure increases by an additional 30 mmHg. Try not to go beyond this mark as it might lead to unnecessary overinflation, which is uncomfortable for a patient. Then, open the valve slowly by rotating it counterclockwise and deflate the cuff at the rate of approximately 2 mmHg per second until the radial pulse returns. Note the manometer reading when the radial pulse reappears and record it on the vital signs flow sheet as the pulse-obliterating pressure.

After this, proceed to obtaining blood pressure with auscultation. Place the chest piece over the brachial artery in the medial aspect of the antecubital fossa. Inflate the cuff again to a level above the pulse-obliterating pressure and confirm that no sound is present. Now, slowly deflate the cuff at a rate of 2 mmHg per second. Listen carefully and note the value on the manometer when the Korotkoff sound can be heard. The manometer reading at that moment corresponds to the systolic blood pressure. Continue slowly deflating the cuff while listening for the sounds to completely disappear. This signifies the diastolic blood pressure. Make sure to deflate the cuff entirely. Record the systolic and diastolic measurements on the vital signs flow sheet.

Normally, the systolic blood pressure on inspiration tends to be lower than that one during expiration due to decreased intrathoracic pressure. However, an abnormally large fall-more than 10 mmHg-in systolic blood pressure on inspiration is defined as pulsus paradoxus, which is most commonly associated with cardiac tamponade or severe chronic obstructive pulmonary disease. To check for pulsus paradoxus, first inflate the cuff to approximately 30 mmHg higher than the previously determined systolic pressure. Deflate at the rate of about 2 mmHg per second. If pulsus paradoxus is present, the first Korotkoff sound is intermittent and occurs just during expiration. Note the reading, which corresponds to higher systolic blood pressure on expiration. Continue to deflate at the same rate until the Korotkoff sounds are audible on both expiration and inspiration-that is, with every heartbeat. Note this reading as well, which corresponds to lower systolic blood pressure on inspiration. Calculate the difference between systolic blood pressure on expiration and inspiration to determine if pulsus paradoxus is present or absent.

Lastly, check for orthostatic hypotension. Place the patient in a supine position and wait for a minimum of 5 minutes before obtaining the reading. Obtain a blood pressure measurement in this position following the method described previously. Record the measurement on the vital signs sheet and make sure to note the position of the patient. Next, request the patient to stand and repeat the blood pressure measurement after 3 minutes of standing. Calculate the difference in pressures. If there is a decrease of 20 mmHg or greater in the systolic pressure or 10 mmHg or greater in the diastolic pressure, then the patient suffers from orthostatic hypotension.

You've just watched JoVE's video on how to accurately measure blood pressure. Despite being a simple and non-invasive measurement, obtaining an accurate blood pressure reading is a skill that requires practice. In addition, correct interpretation of the findings requires good understanding of the physiology and the principles behind this procedure. As always, thanks for watching!