Office Blood Pressure Measurement

Why should I read this chapter in great detail?

“The most important skill you will learn in your medical career is to measure blood pressure. Do it correctly and you will help more patients to better health than with any other skill you learn. Do it wrong and you will harm more patients than with any other medical errors you make over your career.” CE Grim MD 1991: UCLA Preventive Medicine Curriculum, Blood Pressure Measurement Training and Certification Program, First year.

The goal of this chapter is to update your BP skills so you always obtain or are given the most accurate blood pressure. In our 40 years’ experience in assessing and updating practicing physician’s (and their staff’s) skills in BP measurement, it is very likely that you did not receive the detailed training and guided practice needed to master this skill nor has your ability to measure BP accurately been assessed since your initial training. The delegation of this measurement skill to others is acceptable and perhaps preferred but you must have mastered the knowledge and skills to assure that those doing BP for you are doing it correctly. The continual assessment and updating of your and their skills is critical to the delivery of the highest quality cardiovascular care.

We recommend that you do this quick self-assessment because it will provide a guide to areas of knowledge and practice that you need to update. All of these issues will then be covered in detail.

• 1.

  The 2015 SPRINT study tested the hypothesis that lowering systolic BP to less than 120 mm Hg was better than to a goal of 120 to less than 140 mm Hg. The study was stopped early because the lower group had markedly lower rates of death, stroke and congestive heart failure. What was unique about the BP measurement protocol used to diagnose and treat these patients? (BP was measured by the Omron 907 device after resting for 5 minutes with no one else in the room. Three measurements were taken and averaged).

• 2.

  You measure the BP with your patient seated on the edge of the examining table. How much and in which direction will this change the BP reading compared with measuring the BP with the patient properly seated in a chair?

• 3.

  On the average, what percent of patients who have BP measured by an AAMI (Association for the Advancement of Medical Instrumentation)-approved automatic BP device will the BP recorded be off by more than 5 mm Hg? That is in your patients with a true diastolic pressure of 90 mm Hg, in how many will the automated reading the device records off by more than 5 mm Hg? 5%, 12%, 25% 50%?

• 4.

  The recommended gold standard for office blood pressure measurement by the latest AHA is: (1) The auscultatory method using a mercury manometer? (2) Any electronic device that has been validated as accurate by the AAMI?

• 5.

  Why should BP be measured in both arms at the first visit?

• 6.

  Which head of your stethoscope has been shown to be most accurate in detecting the BP sounds?

• 7.

  How accurately do you want your staff to measure your patient’s BP? Within 2, 4, 6, 8 or 10 mm Hg?

• 8.

  How accurate do you want the device used by your staff to measure BP? Within 2, 4, 6, 8 or 10 mm Hg?

• 9.

  Once an office BP above 140/90 mm Hg is recorded in a previously normotensive patient what is the next step recommended to confirm the diagnosis before starting treatment? More office readings, home self BP readings, 24-hour ambulatory BP readings.

• 10.

  If your staff positions the center of the BP cuff on your patient’s arm correctly at heart level but this is two inches lower than used by your referring doctor’s office staff, will the BP measured in your office (all other things being equal) be higher or lower? By about how much?

• 11.

  How does your staff validate that the automatic BP device used in your office or by your patient is “accurate enough” for your guidelines on each patient?

The role of a physician measured BP has diminished with the introduction of automated devices and time crunches on physician time. Yet most practitioners do not realize that the auscultatory method is still the gold standard because no automatic device has been shown to be as accurate and reliable. Nor do they understand that all automatic devices must be validated as accurate in each patient using the gold standard auscultatory method. This can only be done by auscultation. Either you or someone on your team must be designated as the gold standard to assure that your patients receive the best of cardiovascular care. This chapter will enable you to update your knowledge and skills in BP measurement as well as to assure that your staff is up to date.

Blood pressure (BP) ranks third (after age and tobacco use) as predictors of mortality and percent of life spent suffering from the cardiovascular complication of an unhealthy BP (duration of suffering from cardiovascular disease [CVD]). The reason to measure a patient’s blood pressure is to identify if it is unhealthy (which we call hypertension or HTN) as proven by studies showing lowering that level of BP decreases the risk of the CVD because of HTN and increases length of life and decreases disability because of HTN complications. An accurate measurement of BP is essential to assure your patients are not denied the proven benefits of detecting and treating HTN. Unfortunately, BP measurement is almost never performed according to recognized guidelines, published by the AHA periodically since 1938. The World Hypertension League recently issued guidelines for manufacturers to develop an accurate and reliable BP-measuring device for use in low resource settings, because high BP is now the leading cause of death and disability in every country in the world. We argue that such a device currently exists: a trained health care worker using an accurate manometer and a stethoscope. These recommendations stress that every clinic must have a trained BP observer who can validate accuracy of all automatic devices as well as anyone who does auscultatory measurements.

A Brief History of More than a Century of Blood Pressure Measurement

In the early 1900s, with the advent of standardized methods for measuring BP, it became apparent that elevated BP was an important predictor of premature death and disability in patients who reported feeling ill. In 1904, Theodore C. Janeway, the first full time professor of Medicine at Hopkins, published the first clinical text on how to measure BP by simply palpating the radial artery using an inflatable cuff and a mercury manometer. The point at which the pulse disappeared on inflation and reappeared on deflation was the “palpated systolic pressure.” He then reported eight years later on his observations of morbidity and mortality of 7872 symptomatic patients that he and his father had followed. The 870 hypertensive “well-to-do” patients all had a BP greater than 160 and were followed for nine years. From this analysis, he suggested the term “hypertensive cardiovascular disease.” He noted that 53% of men and 32% of women with symptomatic hypertension died in this 9-year period, and 50% of those who died had done so in the first 5 years after being seen. Cardiac insufficiency and stroke accounted for 50%, and uremia for 30%, of the deaths. Thus even a systolic BP determined only by palpation was a remarkable way to predict further cardiovascular death. By 1914, the life insurance industry had learned that even in asymptomatic men, the measurement of BP was the best way (after age) to predict premature death and disability. The goal of the life insurance industry is to insure people who are going to live the longest and not insure those who are at risk in dying prematurely. BP quickly emerged as the best way to do this. Soon all insurance examiners were required to measure BP before a person could obtain a life insurance policy. In 1913, the Chief Medical Officer of the Northwest Mutual Life Insurance Company stated, “No practitioner of medicine should be without a sphygmomanometer. This is a most valuable aid in diagnosis.” In 1918, the Medical Director of the Metropolitan Life Insurance Company ordered 1000 Baumanometers from the WA Baum Company for their medical examiners to use for screening applicants to assure that they were only insuring those at the lowest risks at standard rates.

Population-based studies to investigate the role of the factors that predict those who will develop CVD began in 1948 with the Framingham Heart Study. A single BP was measured at the first visit by auscultation with a mercury manometer by a trained physician. Within 6 years it was clear that this single BP was the key predictor of future CVD and the risk increased continuously from the lowest to the highest levels of systolic BP. All of the predictive information was contained in the systolic BP. Furthermore, when BPs were averaged over more visits (examinations were every two years) the better the systolic BP predicted outcomes. At least 91% of those who developed heart failure (HF) had high BP before they developed overt HF. A recent report from Minnesota suggests that the 10-year trajectory of BP may be an even better predictor of years of life lost from CVD. The impact of BP is even more devastating in African Americans in Evans County, Georgia, where 40% of all deaths in African American women were attributed to high BP. Before the advent of effective BP medications, only severe sodium restriction had been demonstrated as an effective way to reduce BP to normal levels and rapidly reverse advanced CHF. However the discovery of drugs in the 1950s that lowered BP, led to the implementation of large-scale trials in the 1960s to determine the level of BP at which the risks of lowering it outweighed the risks of not lowering it. These early trials attempting to modify the natural history of hypertension (see Chapter 18 ) required design and implementation of mechanisms to ensure that all personnel at the many study centers would measure BP with the highest accuracy and reliability over 5 years. Methods of training developed for these and other trials, as well as for the population-based National Health And Nutrition Examination Surveys (NHANES), evolved into a standardized training, certification, and quality assurance program. The lessons learned from these training programs have yet to be transferred to the basic training of those who take BP in the practice of medicine today. A video and CD–based training and certification program has been based on their experiences. Implementation of these training and certification programs for personnel working in NHANES has improved the quality of BP measurements in this important program. The States of Michigan and Arkansas have adapted the program to an online venue, to improve the quality of BP measurement in clinical practice (see www.michigan.gov/hbpu for more details; the program is also available online at http://sharedcare.trainingcampus.net ). In Arkansas public health nurses’ knowledge and ability to read auscultatory BP was markedly improved by this 1-hour online program. One nurse noted that she had been measuring BP incorrectly for over 30 years!

In most large-scale hypertension trials, the difference in BP between the treated and untreated groups over 5 years has been less than 10/5 mm Hg. Thus errors of this magnitude, if falsely low, will deny the proven benefits of treatment to millions of people who truly have high BP but who will be incorrectly told that their BPs are not high enough to warrant treatment. See Fig. 9.1 and later discussion.

Automated indirect BP by the oscillometric method (see Chapter 10 ) was first described in 1979 by Ramsey in which the pulse wave oscillations transmitted from the artery under the cuff were converted into estimates of systolic and diastolic BP. Unfortunately the algorithm used by automated devices differs by manufacture and different devices often do not get the same reading on the same person and are often inaccurate in practice. To assure that such devices were “accurate enough” for clinical use the AAMI established that devices that pass their validation be unlikely to read off by more than 10 mm Hg too high or too low. The gold standard used by AAMI and recommended by the AHA continues to be auscultatory technique.

The Importance of Careful Blood Pressure Measurement for the Health Care System

Fig. 9.1 illustrates the effect of a “small” (5 mm Hg) systematic BP measurement error on the prevalence of hypertension in the largest nationwide screening program for hypertension ever performed, which is still reflective of the U.S. health care system. The horizontal axis is diastolic blood pressure (DBP) in 5 mm Hg intervals. The vertical axis is the percentage of the U.S. population (in 1983) who had a DBP in each 5 mm Hg interval. The vertical yellow line at 90 mm Hg divides the population into those with a DBP 90 mm Hg or higher, who are diagnosed as hypertensive. In this sample, 25% of adults (∼50 million persons) had a DBP of 90 mm Hg or higher. If the BP was measured “only” 5 mm Hg too high, then those with a DBP of 85 to 90 mm Hg would have been told they had hypertension. This would have increased the number of Americans diagnosed with HTN by 54% (∼27 million) who should have their BP lowered. In other words, the American hypertensive population would have been (erroneously) increased by 54%. This would add a tremendous burden (in time, cost, and effort) to the health care system. If the error was such that DBP was measured systematically “only” 5 mm Hg too low, then those with a DBP from 90 to 95 mm Hg would have been labeled as being not hypertensive, and 42% of all truly hypertensive people would be denied the proven benefits of BP lowering. Because a trained human using a mercury manometer is still the gold standard for BP measurement, and the overwhelming majority of our clinical trial database has been based on this method, true disciples of evidence-based medicine should insist on using this technique to measure BP, rather than accept other methods of BP measurement. The recent SPRINT trial may have changed this as only an automated device was used to enroll and adjust medications during the trial.

Environmental Concerns About Elemental Mercury in the Medical Workplace

Since the early 1990s, regulatory authorities (including the U.S. Occupational Health and Safety Administration) have urged reduction/removal of mercury and other known toxic substances from all workplaces. In some jurisdictions (e.g., Sweden, Minnesota) and health care systems (e.g., U.S. Department of Veterans Affairs Medical Centers), mercury sphygmomanometers have been prohibited and are being replaced. The contribution of mercury manometers to the global mercury burden must be extremely small, and much smaller than the contribution of the widely recommended mercury-containing, low-energy light bulbs. Nevertheless, the state of Washington forbids the purchase of a new mercury manometer unless it is replacing one already in service. On the other hand, Michigan permits every physician’s office to have one mercury device for calibration. This presents both challenges and opportunities.

The obvious benefit of removal of the known toxin, elemental mercury, is that health care workers will no longer be exposed to even low levels of mercury vapor. Chronic inhalation of mercury vapor has been linked to decreased mental acuity, renal impairment, peripheral neuropathy, and death. Problems have not been reported with mercury exposure from BP devices, except among individuals who repaired them many years ago in unventilated facilities. The clear concern is that the mercury sphygmomanometer will be difficult to replace. This traditional, very accurate, highly reproducible, and simple method of measuring BP has been the standard technique for measurement of office BP for more than 100 years. In fact, the design of the mercury sphygmomanometer is essentially unchanged today from what was used 100 years ago, except that today’s instruments are less likely to discharge liquid mercury, particularly if dropped. Because of the constant density of mercury at all altitudes and inhabitable environments, and its universal function as “the standard” in all pressure measurements in every branch of science, there is little difference in accuracy across brands, which is certainly not the case with other types of sphygmomanometers. Despite the simplicity of the mercury sphygmomanometer, it must be properly maintained and cleaned occasionally. A survey of mercury sphygmomanometers in Brazilian hospitals found 21% of the devices with technical problems that could reduce their accuracy, a similar study in England found more than 50% of mercury columns that were defective. However the majority of the problems with these devices were related to the bladders, cuffs, and valves, and not the mercury manometers themselves. Thus even when mercury devices are replaced, the office/health system must implement quality control measures for all parts of BP devices that most commonly malfunction.

Unfortunately, there is currently no generally accepted replacement for mercury manometers, and the most recent set of guidelines from both Europe and the AHA continue to recommend the use of mercury, if available. Although the most recent report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC 7) has not fully endorsed the use of alternatives to the mercury sphygmomanometer, newer BP measurement devices (that do not contain mercury) are being adopted in many centers. Unfortunately, very few “professional” BP measurement devices have been thoroughly tested or proved as reliable, accurate, and long-lived as the mercury column. Few automated sphygmomanometers have been validated as accurate in children using Korotkoff phase IV or phase 4 (muffling), as required by the newest AAMI standards. Most of the inexpensive devices currently on the market are meant for home use, where they may be activated perhaps once daily. These are probably neither accurate nor durable enough to be recommended for a busy health care facility, at which BP is measured hundreds of times a day. Nevertheless, such home devices are widely used in offices, especially in geriatric facilities. Because there is no gold standard home electronic device, seven different home BP devices have been tested on a single subject over several weeks, to determine if the average home BPs measured by the devices were similar. Unfortunately, the average 2-week home BP estimated by these devices varied by 31 mm Hg for systolic bool pressure (SBP) and 19 mm Hg for diastolic blood pressure (DBP). Thus the practitioner must validate, in each patient, every automatic device used to make medical judgments. One electronic device that looks like a large aneroid manometer has been validated. The long-term accuracy, durability, drift, and hysteresis problems have not been reported in this or any other electronic BP monitor. Inexpensive aneroid sphygmomanometers are susceptible to damage (particularly after being dropped to the floor), resulting in inaccurate measurements that are not easily recognized. These devices are most commonly used by home health care professionals, such as visiting nurses. Rubber guards and regular calibration have been recommended for these devices. Even validated oscillometric devices will make large errors (>10 mm Hg) in many individual patients. The term Unreliable Oscillometric Blood Pressure Measurement (UOBPM) was coined by Sterigou in 2006 when they made the observation that one of the most widely used devices, the BPTru, made errors in which the average of three readings made by the device (compared with the gold standard simultaneous auscultated BP) exceeded 10 mm Hg in at least 40% of subjects. In a detailed analysis of the AAMI validation protocol it was pointed out that up to 50% of readings can be expected to be off by at least 5 mm Hg. It is thus necessary to assess the accuracy of any automatic device on every patient to be certain it is accurate enough to be used to diagnose and treat BP in them. The new revisions of both the European Society of Hypertension (ESH) and the AAMI protocols will increase the number of home devices that will not be able to pass standards. An analysis of the new ESH protocol standard increased the failure rate of published devices on the market from 17% to 42%. The major reason for failure was the requirement that, when tested on 33 subjects, only three could have all three readings by the device that differ by more than 5 mm Hg from sequential human readings that bracket each device reading. The new and more stringent AAMI validation protocol tests the probability (at the 15% level) that a device will have an error greater than 10 mm Hg. The statistical testing protocol is based on the historical definition of a “clinically significant” error in BP measurement of more than 10 mm Hg when AAMI first set their standards. This should now probably be lowered to a minimum of a 5 mm Hg tolerable error, to minimize the likelihood that automatic devices will not overestimate or underestimate BP by more than 5 mm Hg in most patients. Current recommendations from both the AHA and European Expert Committees recommend that whenever a sphygmomanometer that does not contain mercury is to be used, it should be checked regularly against a standard mercury column to ensure accuracy. Even electronic calibrators must be regularly calibrated against mercury to assess and correct for electronic drift over time. There is currently no recommended standard to use in the clinic to calibrate a manometer other than a mercury device.

How Can the Measurement of Blood Pressure be Improved in Clinical Practice?

The most recent AHA guidelines include these important conclusions :

In view of the consequences of inaccurate measurement, including both the over-treatment and under-treatment, it is the opinion of this committee that regulatory agencies should establish standards to ensure the use of validated devices, routine calibration of equipment, and the training and retraining of manual observers. Because the use of automated devices does not eliminate all major sources of human error, the training of observers should be required even when automated devices are used.

Although BP measurement is taught in all schools for health care professionals, from office assistant to medical school, correct measurement techniques, according to the AHA’s Guidelines, are almost never taught and therefore never practiced. This may be the result of failure to initially master the knowledge, skills, and techniques needed to obtain an accurate BP measurement, and the lack of periodic retraining and reevaluation thereafter, which the AHA recommends on a semi-annual basis. Neither beginning medical students who claim to have learned proper BP measurement technique, nor practicing nurses in Australia or Taiwan, nor physicians in India, nor general practitioners in Newfoundland, nor practicing public health nurses in Arkansas had sufficient knowledge to pass a standardized test regarding correct technique in BP measurement. Instruction in BP measurement should be provided in a standardized fashion, in compliance with current AHA guidelines.

The importance of retraining and retesting was illustrated in the British Regional Heart Study, in which simultaneous BP readings were taken by trained nurses and a triple-headed stethoscope during training. Immediately after the initial training, the interindividual variability in the field ( Fig. 9.2 ) was very small, but it increased progressively during the next 6 months. After the preplanned retraining session at 6 months (see Fig. 9.2 ), interindividual variability decreased again, nearly to baseline levels. However, because the nurses considered the training tedious and unnecessary, the second retraining session, scheduled for 12 months, was not held. At 14 months into the study, however, the SBPs recorded by observer 1 and 2 differed by an average of 21 mm Hg. After retraining at 18 months, the interindividual variability returned to 0 mm Hg. The authors suggested that retraining and retesting should be done every few months for research studies, but this might not be feasible in routine medical practice. We disagree because their data was used only for epidemiologic research whereas the office and home BP is used to diagnose and guide treatment in the most common chronic disease in the office. This led to the development, testing, and publication of a video-tutored program that teaches the AHA guidelines and tests mastery of the knowledge, skills, and techniques required to obtain accurate and reliable BP readings. The program requires 6 to 8 hours of contact time, but few curricula in medical, nursing, or health aide professions devote sufficient time to practice and then test a student’s mastery of this critical skill. Once trained, few if any curricula retest this skill before graduation, and few health care systems require any retesting or update in knowledge once entering the health care delivery system. Periodic equipment maintenance and observer quality assurance programs should both be part of the curriculum.

Blood Pressure Measurement: Proper Technique for Quality Assurance and Improvement

This section summarizes our published curriculum that reviews, reinforces, and tests the knowledge, skills, and technique needed to obtain an accurate BP. It is based on the AHA recommendations for BP measurement and many years of experience teaching these skills and certifying practitioners around the world in practice or for research studies funded by the National Institutes of Health, the pharmaceutical industry, and public and private health care delivery systems.

Many assume that using an automatic BP measurement device eliminates human error. However, except for those principles and skills needed to perform the auscultatory BP measurement, all of the steps required to get an accurate BP by auscultation must also be followed when an automated device is used. Indeed, unless the guidelines are followed, using an automatic device will give unreliable data as well.

Critical Skills for Any Blood Pressure Observer

Any person who measures BP or interprets the readings made by others must possess the skills, knowledge, and mastery of techniques summarized in Fig. 9.3 . Proper measurement of BP involves coordination of hands, eyes, ears, and mind, and deficits in any one of these areas can lead to imprecise and erroneous measurements. In testing of “experienced” observers, some persons were identified who could not hear well enough to recognize Korotkoff sounds. Other individuals could not remember the SBP without writing it down during cuff deflation. Staff in every practice setting can be screened initially and annually for these problems by testing with standard videotapes and multiearpiece stethoscope BP measurements (described later) and direct observation of the individual’s technique. An online update is also available.

Manometers and their Calibration

A mercury manometer, two aneroid gauges (one intact and one with the face removed), and an electronic BP measuring device are shown in Figs. 9.4 and 9.5 . The mercury manometer is the primary (reference) standard for all pressure measurements in science, industry, and medicine. The pressure is read at the top of the liquid mercury meniscus to the nearest 2 mm Hg. Practitioners who measure BP with nonmercury devices should have at least one reference mercury device available to check other devices regularly, or have an electronic calibration device that can be traceable directly to the mercury standard. The tube containing the mercury should be large enough to allow rapid increases and decreases in pressure. The 2-mm graduated markings should be on the tube itself. The standard glass tube, which can break, should be replaced with either a Mylar-wrapped glass tube or a plastic tube. The inside view of the aneroid device (see Fig. 9.4 ) shows a delicate system of gears and bellows that can easily be damaged by rough handling. Such devices also develop metal fatigue with time, which leads to inaccuracy. In a recent survey in German hospitals, 60% of aneroid devices were out of calibration and the error was almost always reading too low. To detect an inaccurate aneroid device, inspect the face for cracks and be sure the needle is at zero. If it is cracked or does not read zero, it will nearly always be inaccurate and should be recalibrated before reuse. Once an aneroid device is out of calibration, it is difficult to detect the direction of the variance without calibrating it against a mercury or other reference standard. This process is uncommon in both the United States and Europe. It has been alleged that, “clinicians using equipment which has not been maintained and calibrated may be medically negligent,” but this has not been legally tested.