|Home | About | Journals | Submit | Contact Us | Français|
A woman, age 72 years, has blood pressures of 150/70 mm Hg and 150/80 mm Hg, obtained by a medical assistant (MA), on consecutive office visits and does not have a history of hypertension. The blood pressure cuff is properly sized, the MA is inquiring about the patient's last mammogram while obtaining the blood pressure, and the patient is helping to hold her arm up within the MA's grasp. The mean of a dozen blood pressure readings that the patient has obtained at home is 128/64 mm Hg. Does this patient have white-coat hypertension?
The most important commonly performed office test is blood pressure measurement, yet it is considerably undervalued. In the Kaiser Permanente Southern California (KPSC) Region, more than 2,300,000 blood pressure measurements were obtained by office staff in March 2009 (Ralph S Vogel, PhD, personal communication, 2009 April).a MAs often work in a rushed atmosphere, and physicians want their patients to be roomed promptly. However, populationwide, small inaccuracies in blood pressure measurement can have considerable consequences. Underestimating true blood pressure by 5 mm Hg would mislabel more than 20 million Americans with prehypertension when true hypertension is present. It has been predicted that the consequences of an untreated 5 mm Hg of excessive systolic blood pressure would be a 25% increase over current levels of fatal strokes and fatal myocardial infarctions for these individuals.1 Conversely, overestimating true blood pressure by 5 mm Hg would lead to inappropriate treatment with antihypertension medications in almost 30 million Americans, with attendant exposure to adverse drug effects, the psychological effects of misdiagnosis, and unnecessary cost.2
The trap is that in acknowledging the consequences of small measurement inaccuracies, errors of 5 to 10 mm Hg commonly occur as a result of improper blood pressure technique. Table 1 lists blood pressure aberrancies as a result of common errors. For example, active listening by the patient, when the MA is talking during blood pressure measurement, can increase systolic blood pressure by 10 mm Hg.3 Obtaining a measurement from an unsupported arm can increase the systolic pressure by 10 mm Hg. Lack of back support and crossed legs increase blood pressure. If a patient needs to urinate, a blood pressure measurement taken before bladder emptying can increase the systolic pressure by >10 mm Hg. Measurements taken over clothing or with tight clothing pushed up on the arm, causing a tourniquet effect, also produce significant artifacts.4 However, although many textbooks state that the bell of the stethoscope is more reliable than the diaphragm, studies show that is not the case.5,6 The commonplace use of the diaphragm side of the stethoscope is satisfactory. Figure 1 illustrates the proper technique for obtaining a sitting blood pressure.
… overestimating true blood pressure by 5 mm Hg would lead to inappropriate treatment with antihypertension medications in almost 30 million Americans, with attendant exposure to adverse drug effects, the psychological effects of misdiagnosis, and unnecessary cost.2
Terminal digit preference, a common source of error during manual blood pressure examinations, is the rounding off of numbers to the nearest zero. Usually the result is an inappropriate increase in the diagnosis of hypertension because systolic pressures in the upper 130s are rounded up to 140 mm Hg. In a KPSC blood pressure survey, 22% of recorded blood pressure numbers ended in zero; the expected occurrence would be 10%. Those results are better, however, than those from one literature survey, which reported that 78% of recorded blood pressure numbers terminated in zero.7,8 Although studies have been reported showing that an automated oscillometric device that provides five serial blood pressure measurements reduces the white-coat effect compared with manual determinations,9,10 another study has shown that blood pressure is underestimated by this device, leading to significant misclassification of hypertension.11 The use of an automatic blood pressure monitor does have the advantage of obviating terminal digit preference,12 but the plethora of potential patient preparation errors still remain.
“… if the standing blood pressure is consistently much lower than the sitting blood pressure, the standing blood pressure should be used to titrate drug doses during treatment.”15
What about taking a forearm blood pressure on an obese patient? Nurses often find that it is faster and easier to take a forearm blood pressure than to search for a larger cuff. Studies have shown that forearm blood pressures generally run 3.6/2.1 mm Hg higher than upper arm blood pressures.13,14 The experience in KPSC has been that once clinicians and MAs are taught how to obtain forearm blood pressures, inappropriate usage of forearm pressures becomes commonplace. Therefore, we no longer teach this technique. Instead, the regional mandate is to have both standard and large blood pressure cuffs in every primary care examination room. Using a standard blood pressure arm cuff on an obese patient falsely raises systolic blood pressure by approximately 10 mm Hg. “Miscuffing” should be strongly discouraged.
For which patients is a standing blood pressure measurement most appropriate, and what is the proper technique for obtaining one? Particularly in patients who are ≥70 years old and taking antihypertension medications, obtaining standing blood pressure measurements should be routine practice. Although the sitting blood pressure measurement represents the standard in hypertension treatment trials, standing systolic pressure decreases of ≥20 mm Hg, consistent with a diagnosis of orthostatic hypotension, commonly occur and raise safety and quality-of-life issues in geriatric patients already at risk for dizziness and falling. Therefore, the National High Blood Pressure Working Group report on Hypertension in the Elderly concluded “… if the standing blood pressure is consistently much lower than the sitting blood pressure, the standing blood pressure should be used to titrate drug doses during treatment.”15 An international neurology consensus statement endorsed waiting “within three minutes” in the standing position16 and others have clarified this recommendation as being three minutes,17 but the protocol used in the landmark HYpertension in the Very Elderly Trial (HYVET) waited two minutes.18 Having patients stand for two to three minutes before their upright blood pressure measurement is taken is reasonable for hypertension management. When blood pressure is properly measured in the standing position, the arm should be supported (Figure 2). When measurement is taken on a dangling arm, the systolic pressure may artifactually be 6 to 10 mm Hg higher than in an arm that is properly supported.19,20
Who should be measuring the blood pressure after all, physician or nurse? In all of the hypertension treatment trials, blood pressure has been measured by trained nonphysicians, usually nurses. White-coat effect is common and persistent. In a classic study of nurse and physician blood pressures undertaken in patients with continuous intra-arterial blood pressure monitoring, two concurrent measurement phenomena were observed: observer effect and alerting reaction (Figure 3). After a few minutes, a repeat blood pressure measurement obtained by both a physician and a nurse produced results about 10/5 mm Hg lower than the first determination, owing to mitigation of the alerting reaction. Nonetheless, there was a difference of 10/5 mm Hg between the physician and the nurse with both the first and second determinations, demonstrating the persistence of the observer, or white-coat, effect.21 Patients are more afraid of physicians than of nurses. If an initial blood pressure reading obtained by an MA is elevated and a physician then obtains a follow-up reading, that second reading may be lower because the alerting reaction has subsided, or it may be higher because of doctor-related white-coat effect. Physicians taking blood pressure measurements should be knowledgeable regarding proper technique and the causes of artifacts.
Multiple competent blood pressure measurements by MAs can obviate the white-coat effect. Two studies have shown that several measurements obtained by nurses can approximate mean blood pressure measurements obtained by 24-hour ambulatory blood pressure recordings.22,23 The discrepancy between office blood pressure measurements and 24-hour ambulatory measurements is at least in part because of poor office competence in obtaining accurate readings. When there is concern regarding the possibility of the white-coat effect, having MAs obtain weekly blood pressure measurements for two weeks should be considered. Whenever the first blood pressure reading is elevated, a second reading should be obtained after a one-minute interval.
Patients are increasingly helpful as quality-assurance monitors. Educational materials are available to teach proper home blood pressure measurement technique, and other general patient-education materials demonstrating blood pressure measurement competency have been distributed. On a few occasions, we have received accurate criticism of blood pressure measurement technique performed by our staff from patients in KPSC. Also, peer-validator competency review of blood pressure measurement by
MAs is expanding in our system: MAs receiving peer-validator training offer critiques and instruction to their colleagues in a program that has generated positive feedback from participants. Additionally, a new blood pressure measurement training video is being developed, with “train-the-trainer”8 Webinars planned for later in 2009.
The patient whose case was presented at the beginning of this article does not have hypertension despite the elevated office readings, and she does not need home blood pressure measurements for a diagnosis of white-coat hypertension to be made. White-coat hypertension indicates a dissociation between competently determined office blood pressure elevations and normal blood pressure readings obtained at home. Therefore, findings for this patient do not qualify for a diagnosis of white-coat hypertension, because the office blood pressure readings are inaccurate. Terminal digit preference is a marker of inaccurate office technique: all four office measurements for the patient ended in zero. Active listening by the patient, from whom medical information was requested during blood pressure measurement, and partial patient support of her outstretched arm could easily have accounted for a systolic artifact of >10 mm Hg. This patient was exposed to the possibility of receiving an inaccurate diagnosis of hypertension and taking inappropriate antihypertension medications. Her case illustrates potential patient care problems ensuing from poor office blood pressure measuring technique.
If an initial blood pressure reading obtained by an MA is elevated and a physician then obtains a follow-up reading, that second reading may be lower because the alerting reaction has subsided, or it may be higher because of doctor-related white-coat effect.
Take a minute to examine Figure 4 and list all ten errors in obtaining the sitting blood pressure shown. (Key to answers listed below.)
Figure 4. What is wrong with the blood pressure measurement technique in this picture? Key for errors: 1) Patient's arm is unsupported; 2) Patient's back is unsupported; 3) Patient is talking; 4) Patient is engaged in active listening; 5) Wrong size cuff in use (“miscuffing”); 6) Blood pressure cuff is positioned too low on the upper arm; appears to be over the elbow; the artery marker on the cuff is probably malpositioned as well; 7) Cuff is over clothing; 8) Observer is not at eye level with the monitor; where is the monitor? 9) Patient's legs are crossed; 10) End of stethoscope is in clinician's coat pocket.
a Practice Leader, Data Consulting and Report Production, Southern California Permanente Medical Group Clinical Analysis
The author(s) have no conflicts of interest to disclose.
Katharine O'Moore-Klopf, ELS, of KOK Edit provided editorial assistance.