Blood Pressure Measurement


Article Author:
Saad Rehman


Article Editor:
Vivian Nelson


Editors In Chief:
Patricia Maani-Fogelman
Julianne Oates


Managing Editors:
Frank Smeeks
Scott Dulebohn
Erin Hughes
Pritesh Sheth
Mark Pellegrini
James Hughes
Richard Ciresi
Phillip Hynes


Updated:
10/27/2018 12:31:25 PM

Introduction

Blood pressure is a cardinal vital sign that guides both acute and long-term clinical decision-making. Given its importance in directing care, it is essential to measure blood pressure accurately and consistently.

In general, 2 values are recorded during the measurement of blood pressure. The first, systolic pressure, represents the peak arterial pressure during systole. The second, diastolic pressure, represents the minimum arterial pressure during diastole. A third value, mean arterial pressure, can be calculated from the systolic and diastolic pressures.

Equipment

Manual Auscultation

The original method of determining blood pressure via the auscultation of Korotkoff sounds continues to be a mainstay in blood pressure measurement. This method utilizes a sphygmomanometer, a device comprised of an inflatable cuff that is connected to a pressure gauge (generally a column of mercury). To measure an individual’s blood pressure, the deflated cuff is placed around the arm and inflated sufficiently to occlude arterial flow. At this point, the pressure of the cuff exceeds the systolic pressure, and auscultation over the brachial artery reveals no sound due to complete obstruction of flow. The cuff is then gradually deflated while continuing to auscultate over the brachial artery. When the pressure in the cuff falls to the level of the systolic pressure, pulsatile blood flow begins to re-establish. The resulting turbulence produces characteristic tapping sounds known as Korotkoff sounds. As the cuff continues to deflate to the level of the diastolic pressure, pulsatile blood flow occurs smoothly, and Korotkoff sounds disappear. Thus, the systolic pressure is indicated by the origination of Korotkoff sounds, and the diastolic pressure is indicated by their disappearance.

Of note, medical professionals should be aware of the auscultatory gap, a phenomenon which can result in the premature recording of the diastolic pressure. In some patients, particularly those with wide pulse pressure, Korotkoff sounds can temporarily fade but then reappear as the cuff continues to deflate. Medical professionals should thus continue to auscultate over the brachial artery even when Korotkoff sounds disappear to eliminate the possibility of an auscultatory gap. Only the final disappearance of Korotkoff sounds should be used for recording of the diastolic pressure.

Automated Devices

Automated devices can also be used to measure blood pressure. Rather than auscultate for Korotkoff sounds, these devices measure oscillations in blood flow as the cuff is deflated. 

Device-specific algorithms are then used to calculate blood pressure indirectly. An advantage of automated measurements is that they require little user-knowledge and are thus suitable for use by laypersons in non-medical environments.

Invasive Monitoring

The most accurate method of obtaining blood pressure measurements is with the use of an invasive probe that is inserted directly into the lumen of an artery. An advantage of invasive monitoring is the ability to display blood pressure variations with each heartbeat. However, given the invasive nature of this method and the associated risks, its use is limited to critical care or operative settings. As such, the remainder of this review will focus on the previously mentioned methods of blood pressure measurement.

Technique

Blood pressure is remarkably labile. The most insignificant activities can result in substantial changes in blood pressure readings. As such, regardless of whether a manual or automated method is being used to measure blood pressure, medical professionals should always prepare the patient and environment properly before cuff inflation.

First, the patient should be questioned regarding recent caffeine consumption, exercise, or smoking. If any of these activities have occurred within the last 30 minutes, blood pressure measurement should be postponed until this period has passed. Next, the patient should be encouraged to empty his/her bladder. Upon return, the patient should be seated in a quiet room on a chair with back support. Both feet should be flat on the floor with the legs uncrossed, and this seated position should be maintained for at least 5 minutes.

At this time, a properly-sized cuff should be placed directly over the patient’s arm, no clothing should be underneath the cuff, and sleeves should not be rolled above the cuff. Once the cuff is in position, the patient’s arm should be supported so that the middle of the cuff is at the level of the right atrium. Initiation of blood pressure measurement can now occur. The patient should not speak or be spoken to while measurements are being taken.

There is significant variation among automated devices, and users should refer to instruction guides on how to initiate cuff inflation and blood pressure measurement. If a manual measurement is being performed, the bell or diaphragm of a stethoscope should be placed over the medial antecubital fossa over the approximate location of the brachial artery. The blood pressure cuff should be inflated 30 mm Hg beyond the point at which the radial pulse is no longer palpable. Deflation of the cuff should occur in a slow and controlled manner – a rate of 2 to 3 mm Hg per second is recommended. As mentioned previously, the appearance of Korotkoff sounds signifies the systolic pressure, while the cessation of these sounds indicates the diastolic pressure.

Complications

The most common source of error in blood pressure measurement is a failure to adhere to proper technique. Multiple studies have attempted to quantify the impact of common mistakes. Smoking within 30 minutes of measurement can raise the systolic blood pressure up to 20 mm Hg, while a distended bladder can raise both systolic and diastolic measurements by 10 to 15 mm Hg. Sitting in a chair lacking back support can raise systolic blood pressure up to 10 mm Hg, and a similar increase is observed when both legs are crossed. Cuff placement over clothing can affect measurements by an astonishing 50 mm Hg. Talking/listening during measurements can increase both systolic and diastolic measurements by 10 mm Hg. The use of an improperly sized cuff can affect blood pressure in either direction; a larger cuff results in falsely low measurements, while a smaller cuff results in falsely elevated measurements. Similarly, incorrect positioning of the arm also results in a bidirectional error; placing the arm below the level of the right atrium results in higher values, whereas placing the arm above the level of the right atrium generates lower values. The vast ranges of these errors highlight the importance of adhering to appropriate technique when measuring blood pressure.

In addition to the modifiable source of error above, there are also unavoidable sources of error. Multiple studies have found differences between measurements obtained in clinical settings and those taken in ambulatory settings. Hypertension can be inaccurately diagnosed in patients prone to “white-coat hypertension,” a phenomenon in which the apprehension of being in the presence of a medical professional results in a transient rise in blood pressure. These patients are normotensive in ordinary settings and are hypertensive only in clinical settings. Similarly, hypertension can be inadvertently overlooked in patients who appear to be normotensive in the clinic but are hypertensive throughout other points of the day. This “masked hypertension” may be due to lifestyle changes made before medical appointments.

Clinical Significance

Hypertension

When clinically feasible, 2 or more measurements taken at different visits should be used to make a diagnosis of hypertension. The threshold at which high blood pressure is diagnosed is constantly evolving in response to new evidence. Previous guidelines had defined hypertension beginning at a blood pressure of 140/90 mm Hg, but the most recent updates have lowered this level based on the benefits of early intervention. Current thresholds are listed in the table below:

Undiagnosed hypertension places patients at increased risk of developing coronary artery disease, stroke, and end-stage renal disease, among other complications. In the United States, hypertension is the second most preventable cause of death; worldwide, it is the leading cause of death and disability-adjusted life years. Thus, timely and accurate diagnosis of hypertension is essential to initiate treatment that prevents and/or reduces the occurrence of these complications.

Hypotension

Hypotension is less common than hypertension and is generally due to an identifiable cause, such as dehydration, illness, or medication side effect. While there is no formal threshold for the diagnosis of hypotension, a systolic pressure less than 90 mm Hg or a diastolic pressure less than 60 mm Hg is generally used by medical professionals. More commonly, the diagnosis is guided by patient symptoms, including light-headedness, dizziness, blurred vision, nausea, and weakness.

Orthostatic Hypotension

Some patients are normotensive at rest but experience symptoms of hypotension when standing. Such orthostatic hypotension is defined by a decrease in systolic blood pressure of 20 mm Hg or decrease in diastolic blood pressure of 10 mm Hg after three minutes of standing from a sitting or supine position.


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Blood Pressure Measurement - Questions

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Which of the following correctly pairs a Korotkoff sound with its corresponding blood pressure parameter?



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At a follow-up visit, a 7-year-old male has moderately high blood pressure compared to his last visit. What is the next step?



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What is the normal blood pressure for those who are 18 years of age or greater?



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Which of the following goals is important when expanding the cuff of a sphygmomanometer?



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A patient’s blood pressure is being measured during a follow-up appointment using a sphygmomanometer. After preparing the patient appropriately, the cuff is inflated above the systolic blood pressure. As the cuff is deflated, Korotkoff sounds are auscultated at a cuff pressure of 132 mmHg. The Korotkoff sounds cease at 90 mmHg but reappear at 80 mmHg before again disappearing at 70 mmHg. Which of the following should be recorded as the patient’s blood pressure?



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A normotensive patient's blood pressure is measured in the supine and erect positions. The expected change in blood pressure in the erect position is a slight:



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An arterial blood pressure determination of 80/60 could result from:



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Which is the correct statement concerning the sphygmomanometer bladder size?



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Which of the following is the most accurate method for measuring blood pressure?



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Which is inappropriate for blood pressure screening?



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The first rotation of a practitioner's medical rotation is on the cardiology service where the chief resident asks for a blood pressure measurement of a patient. Which of the following is used to determine the size of the cuff?



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At which point in the arm is the cuff size measured?



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In an adult, which of the following is correct regarding the Korotkoff sounds when taking the blood pressure measurement manually?



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A patient has had repeatedly elevated blood pressure measurements during her previous three clinic visits. She checks her blood pressure at home daily with an automated device, but the device log confirms consistently normal blood pressure measurements. The patient brings her automated measurement device to the clinic and demonstrates proper use. However, the device shows an elevated blood pressure when used in the clinic, identical to that measured using the office sphygmomanometer. Which of the following is the correct course of action?



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Blood Pressure Measurement - References

References

2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines., Whelton PK,Carey RM,Aronow WS,Casey DE Jr,Collins KJ,Dennison Himmelfarb C,DePalma SM,Gidding S,Jamerson KA,Jones DW,MacLaughlin EJ,Muntner P,Ovbiagele B,Smith SC Jr,Spencer CC,Stafford RS,Taler SJ,Thomas RJ,Williams KA Sr,Williamson JD,Wright JT Jr,, Journal of the American College of Cardiology, 2017 Nov 7     [PubMed]
Recommendations for blood pressure measurement in humans and experimental animals: part 1: blood pressure measurement in humans: a statement for professionals from the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research., Pickering TG,Hall JE,Appel LJ,Falkner BE,Graves J,Hill MN,Jones DW,Kurtz T,Sheps SG,Roccella EJ,, Circulation, 2005 Feb 8     [PubMed]
The importance of accurate blood pressure measurement., Handler J,, The Permanente journal, 2009 Summer     [PubMed]
Blood pressure measurement--an overview., Dieterle T,, Swiss medical weekly, 2012 Jan 27     [PubMed]

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