Source: Meghan Fashjian, ACNP-BC, Beth Israel Deaconess Medical Center, Boston MA
The term blood pressure (BP) describes lateral pressures produced by blood upon the vessel walls. BP is a vital sign obtained routinely in hospital and outpatient settings, and is one of the most common medical assessments performed around the world. It can be determined directly with the intra-arterial catheter or by indirect method, which is a non-invasive, safe, easily reproducible, and thus most used technique. One of the most important applications of BP measurements is the screening, diagnosis, and monitoring of hypertension, a condition that affects almost one third of the U.S. adult population and is one of the leading causes of the cardiovascular disease.
BP can be measured automatically by oscillometry or manually by auscultation utilizing a sphygmomanometer, a device with an inflatable cuff to collapse the artery and a manometer to measure the pressure. Determination of the pulse-obliterating pressure by palpation is done prior to auscultation to give a rough estimate of the target systolic pressure. Next, the examiner places a stethoscope over the brachial artery of the patient, inflates the cuff above the expected systolic pressure, and then auscultates while deflating the cuff and observing the manometer readings. When the pressure in the cuff falls below the pressure in the brachial artery, the turbulent blood flow in a partially squeezed artery produces the Korotkoff audible sounds. The first audible Korotkoff sound signifies the maximum arterial pressure during systole. When the pressure in the cuff is reduced further and falls below the minimal arterial pressure (during diastole), the Korotkoff sounds become no longer audible. The reading at this point signifies the diastolic blood pressure. The blood pressure is measured in mmHg and recorded as a fraction (systolic BP/ diastolic BP).
In most instances, the vital signs are initially measured by a health care assistant or registered nurse (RN). The physician may choose to repeat the vital signs and blood pressure measurement after completion of the patient interview. Repeated measurement of blood pressure is especially important given the potential measurement errors and blood pressure variations.
- Assess for any contraindications to BP measurement in the upper arm including arteriovenous fistula, history of axillary lymph node dissection, or evident lymphedema.
- Make sure the patient has changed into a gown and rested for at least 5 min prior to obtaining blood pressure and other vital signs.
- Ask the patient to sit comfortably with their feet uncrossed and resting on the floor.
- Have the stethoscope and sphygmomanometer ready.
- Confirm proper sizing of the BP cuff (when wrapped around the limb the index line on the cuff should fall within the marked arm circumference range limits). A small cuff may falsely elevate the readings and potentially lead to misdiagnosis.
2. Determination of pulse-obliterating pressure by palpation
Obtaining the pulse-obliterating pressure prior to measurement of blood pressure by auscultation allows avoiding measurement error due to the auscultatory gap. An auscultatory gap is an intermittent disappearance of Korotkoff sounds after their initial appearance before the true diastole, which may seriously underestimate the systolic pressure or overestimate the diastolic pressure.
- Place the cuff on the patient's arm about 2.5 cm above the antecubital fossa.
- Make sure the patient's arm is free of clothing and resting at their side with the brachial artery at the level of the heart.
- Identify the radial pulse with your index and middle fingers.
- Close the valve on the pressure bulb (by turning it clockwise with your thumb) and inflate the cuff by squeezing the pressure bulb rapidly.
- Inflate until the radial pulse cannot be felt anymore and note the measurement on the manometer.
- Continue to inflate until the pressure increases for an additional 30 mmHg. This is done to avoid over-inflation of the cuff on subsequent readings.
- Open the valve slowly by rotating it counterclockwise with your thumb.
- Deflate the cuff at 2 mmHg/sec until the radial pulse returns.
- Record the manometer reading when the radial pulse reappears (obliterating pressure) on the vital signs flow sheet.
3. Obtaining blood pressure with auscultation
- Place the stethoscope over the brachial artery (medial aspect of antecubital fossa).
- Inflate the cuff again at a level of 30 mmHg above pulse-obliterating pressure and make sure no sounds are present.
- Slowly deflate the cuff at a rate of 2 mmHg/sec.
- Note the value on the manometer when the Korotkoff sound, indicated by the first two consecutive beats, 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, which signifies the diastolic blood pressure.
- Make sure to deflate the cuff entirely so as not to miss the diastolic pressure.
- Record the systolic and diastolic blood pressure measurements on the vital signs sheet.
- Repeat the process in both arms (unless contraindicated).
4. Testing for pulsus paradoxus
Normally, the systolic blood pressure is lower on inspiration due to decreased intrathoracic pressure. An abnormally large fall (more than 10 mmHg) in systolic blood pressure on inspiration is defined as pulsus paradoxus and is most commonly associated with cardiac tamponade or severe chronic obstructive pulmonary disease .
- Inflate the cuff to 30 mmHg higher than the systolic pressure determined during blood pressure measurement.
- Deflate at 2 mmHg/sec until the first Korotkoff sound is audible on expiration (sound should be intermittent rather than every heartbeat, corresponding to higher blood pressure on expiration). Note the measurement.
- Continue to deflate the cuff at 2 mmHg/sec until the Korotkoff sounds are audible on both expiration and inspiration (every heartbeat). Lower blood pressure on inspiration is due to a decrease in intrathoracic pressure.
- Calculate the difference between systolic blood pressure on expiration and inspiration.
5. Orthostatic or Postural blood pressure measuring
An orthostatic hypotension is an abnormal decrease in systolic blood pressure of 20 mmHg or a decrease in diastolic blood pressure of 10 mmHg within 3 min of standing compared with blood pressure in supine or sitting position. This can result from compromised venous return and subsequent decrease in cardiac output. Orthostatic hypotension can happen transiently in people of all ages, but occurs most commonly in elderly patients. Some potential causes include blood loss, medications, and disease of the autonomic nervous system.
- Place the patient in a supine position. Wait for a minimum of 5 min before obtaining the reading.
- Obtain a blood pressure measurement as described.
- Record the measurement on the vital signs sheet. Make sure to note the position of the patient.
- Have the patient stand and repeat the BP measurement after 3 min 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, the patient has orthostatic hypotension.
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. One in every three adults in the United States suffers from hypertension and it is one of the leading causes of cardiovascular diseases.
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 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-wise 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 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 mercury level on the manometer. Inflate further until the pressure increases for an additional 30 mmHg. Try not to go beyond this mark as it might lead to unnecessary over inflation, 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 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 the 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!
Applications and Summary
An accurate measurement of BP is essential for timely diagnosis and treatment of the underlying condition. Although patients can sustain higher blood pressure (hypertension) for a longer period of time, which is a key factor in developing cardiovascular disease or stroke, a drastically low (hypotensive) or decreasing blood pressure can be fatal if not treated in time. Despite being a simple and non-invasive measurement, obtaining accurate BP is a skill that requires practice, and correct interpretation of the findings requires good understanding of physiology and pathophysiology behind the principle of this procedure.