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Avoid food intake, strenuous exercise, smoking, and the ingestion of caffeine 30 minutes prior to evaluation.
Cuff size — Use of a properly sized cuff is essential [38,39]. If too small a cuff is used, the pressure generated by inflating the cuff may not be fully transmitted to the brachial artery; in this setting, the pressure in the cuff may be considerably higher than the intra-arterial pressure, which can lead to overestimation of the systolic pressure by as much as 10 to 50 mmHg. Conversely, if too large a cuff is used, systolic blood pressure readings may be underestimated.
The length of the BP cuff bladder should be 80 percent, and the width at least 40 percent (and some use 46 percent), of the circumference of the upper arm [37,40].
We agree with the American Heart Association regarding the appropriate cuff size for a designated arm circumference [41]:
●Arm circumference 22 to 26 cm, "small adult" cuff, 12 x 22 cm
●Arm circumference 27 to 34 cm, "adult" cuff, 16 x 30 cm
●Arm circumference 35 to 44 cm, "large adult" cuff, 16 x 36 cm
●Arm circumference 45 to 52 cm, "adult thigh" cuff, 16 x 42 cm
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Patient position — The BP should be taken with the patient in a seated position with the back supported and legs uncrossed [32]. The diastolic pressure may be higher by 6 mmHg if the back is unsupported, and the systolic pressure may be raised by 5 to 8 mmHg if the legs are crossed [37].
For some patients, particularly older adults and diabetic patients, supine, sitting, and standing BPs are useful to detect orthostatic hypotension [43]. (See "Mechanisms, causes, and evaluation of orthostatic hypotension".)
The arm should be supported at the level of the heart [44]. If the arm is allowed to hang down unsupported, the measured BP will be elevated by 10 to 12 mmHg due to the added hydrostatic pressure induced by gravity [45]. The patient should sit quietly for five minutes before the BP is measured [46]. Bladder distension, talking, and background noise can all affect the measured BP [37].
Even under optimal conditions, many patients are apprehensive when seeing the clinician, resulting in an acute rise in BP. Twenty to 30 percent of patients with hypertension in the clinician's office are normotensive outside of the office [47]. This phenomenon, called "white coat" or isolated office hypertension, should be suspected in any patient with markedly elevated office BP in the absence of end-organ damage or with normal ambulatory BPs taken at work or at home (table 3 and figure 1). The presence of white coat hypertension can be confirmed by 24-hour ABPM or self-recorded readings at home. This white coat effect can usually be minimized by having a nurse measure the BP (figure 2) [48] and by using automated BP devices which record multiple readings with the patient alone in the examination room. This white coat effect can persist for years (figure 3). (See "Out-of-office blood pressure measurement: Ambulatory and self-measured blood pressure monitoring".)
Cuff placement — The BP cuff should be placed with the bladder midline over the brachial artery pulsation [37]. The lower end of the BP cuff should be 2 to 3 centimeters above the antecubital fossa to minimize artifactual noise related to the stethoscope touching the cuff.
Ideally, the cuff should be placed on the bare arm or over a thin sleeve. The patient's sleeve should not be rolled up, as this may act as a tourniquet, nor should the measurement be taken over a thick sleeve, as this may lead to an overestimate of the patient's BP [49].
Technique of measurement — Once the cuff is adequately placed, neither the patient nor the observer should talk during the measurement. The BP should be taken with the patient's arm supported at the level of the heart.
Auscultatory method of measurement — Auscultatory methods depend upon the skill and experience of the operator. The cuff should be inflated to a pressure approximately 30 mmHg greater than systolic, as estimated from the disappearance of the pulse in the brachial artery by palpation [38]. Initial estimation of the systolic pressure by palpation avoids potential problems with an auscultatory gap, wherein the Korotkoff sounds transiently disappear as the cuff is deflated. As an example, the Korotkoff sounds in a patient with a systolic pressure of 180 mmHg may be first heard at 180 mmHg, disappear at 165 mmHg, and then be reheard at 140 mmHg. If the cuff is only inflated to a pressure of 160 mmHg, no sounds will be heard until 140 mmHg; as a result, the latter value will be mistakenly considered to be the systolic pressure.
With the auscultatory method, the stethoscope should be placed lightly over the brachial artery since the use of excessive pressure can increase turbulence and delay the disappearance of sound. The net effect is that the diastolic pressure reading may be artifactually reduced by up to 10 to 15 mmHg.
The cuff should be deflated slowly at a rate of 2 to 3 mmHg per second [50]. The systolic pressure is the pressure at which the pulse is first heard by auscultation (Korotkoff phase I).
As the cuff is deflated below the systolic pressure, the pulse continues to be heard until there is abrupt muffling (phase IV) and, approximately 8 to 10 mmHg later, disappearance of sound (phase V). There is general consensus that phase V should be used to determine diastolic BP in adults [37].
Oscillometric method of measurement — Oscillometric devices have an electronic pressure sensor to record the pressure oscillations of the arteries and automatically inflate and deflate the cuff. Proprietary algorithms are used by these devices to calculate systolic and diastolic BPs.
The BP should be measured initially in both arms. If there is a large disparity due to a unilateral arterial lesion (usually a subclavian stenosis [51]), the arm with higher pressure should be used [52].
A disparity in BP between the arms predicts not only the presence of subclavian stenosis but also a higher risk of cardiovascular disease. In a meta-analysis that included 20 studies, patients who had a BP disparity of 10 mmHg or more between the arms were significantly more likely to have peripheral arterial disease (42 versus 12 percent) [53]. A disparity of 15 mmHg or more was significantly associated with a higher prevalence of cerebrovascular disease (11 versus 4 percent) and a significantly greater relative risk (RR) of cardiovascular death (RR 1.63, 95% CI 1.10-2.41).
The BP should be taken at least twice during each office visit, with the measurements separated by one to two minutes to allow the release of trapped blood. If the second value is more than 5 mmHg different from the first, continued measurements should be made until a stable value is attained. The recorded value on the patient's chart should be the average of the last two measurements.
Need for multiple measurements — In the absence of end-organ damage, the diagnosis of hypertension should not be made until the BP has been measured on at least three visits, spaced over a period of one week or more [54].
Sequential studies have shown that the BP drops by an average of 10 to 15 mmHg between the first and third visits in newly diagnosed patients, with a stable value not being achieved in some patients until more than six visits [55]. Thus, many patients considered to be hypertensive at the initial visit are in fact normal. (See "Out-of-office blood pressure measurement: Ambulatory and self-measured blood pressure monitoring".)
In addition, multiple measurements are necessary when monitoring patients who are already on treatment for hypertension. A study of 444 men with longstanding, poorly controlled hypertension found that a single clinic or home systolic BP of 120 to 157 mmHg had less than an 80 percent chance of correctly classifying the patient as being in or out of control [33]. Correct classification was maximized at five to six measurements, with most of the benefit occurring with the second measurement.
If the BP is taken at home to establish the diagnosis of hypertension or to assess BP control, at least 12 to 14 measurements should be obtained, with both morning and evening measurements taken over one week. Home BP monitoring is discussed in detail elsewhere. (See "Out-of-office blood pressure measurement: Ambulatory and self-measured blood pressure monitoring".)
Alternative sites for measurement — BP can be measured in the leg or wrist.
Leg blood pressure — There are occasional patients in whom the BP needs to be measured in the legs. The classic example is with suspected coarctation of the aorta in which there is an arm-to-leg gradient, but it is more commonly required in patients who cannot have BP measured in the arms (eg, due to surgery, indwelling catheters, vascular fistulae, or grafts). (See "Clinical manifestations and diagnosis of coarctation of the aorta", section on 'Blood pressure and pulses'.)
The principles of BP measurement in the leg are similar to those described above in the arm, with use of an appropriately sized cuff. (See 'Cuff size' above.)
In normal subjects, the systolic pressure in the lower extremity is usually higher than that in the brachial artery [56]. In a systematic review of 44 studies comparing arm and leg BP readings performed in the supine position, mean systolic BP was higher in both the calf (by 10 mmHg, 95% CI 4 to 16 mmHg) and the ankle (17 mmHg, 95% CI 15 to 21 mmHg) than in the arm [57]. However, the high variability in arm-leg BP difference in these studies can make it difficult to reliably translate leg pressures into arm pressures. In addition, no oscillometric BP monitors have been validated for lower-extremity BP measurements.
In patients with vascular disease, systolic BP at the ankle is often lower than the BP in the arm [57,58]. (See "Noninvasive diagnosis of upper and lower extremity arterial disease", section on 'Lower extremity segmental pressures'.)
Wrist blood pressure — Measurement of BP at the radial artery (wrist) may sometimes be necessary in people with obesity (when a sufficiently large cuff cannot be obtained, such as when measurement devices are purchased for home monitoring) and in patients with breast cancer who have had axillary lymph node resection [29]. However, given questions about accuracy, BP measurement at the wrist should not be used routinely if brachial BP measurement is feasible.
Technical considerations may make accurate measurement of BP at the wrist more challenging than measurements taken at the brachial artery [37]. At the wrist, the hydrostatic pressure related to the lower position of the wrist relative to the heart can result in a further false elevation of BP. This can be minimized by taking the BP with the wrist kept at the level of the heart. In addition, an automatic device's sensor must remain directly over the radial artery for an accurate reading, and wrist flexion may interfere with appropriate sensor positioning.
Automated office blood pressure measurement — AOBP devices utilize oscillometric methodology and take multiple consecutive BP readings in the office with the patient sitting and resting, preferably alone (ie, unattended). Compared with conventional manual office measurements, unattended AOBP decreases the white coat response, avoids talking during the rest and measurement periods, and avoids observer error and bias [7,13,59]. Available AOBP devices differ in the number of readings taken and the number of minutes before the first BP measurement is recorded [34,60]. Evaluation of machine accuracy should be performed at periodic intervals. BP monitors that have been validated in accordance with the standards published by the Association for the Advancement of Medical Instrumentation, the ANSI/AAMI/ISO, or British Hypertension Society protocols should be used. Useful information about the various AOBP devices that are marketed can be found here and here.
Proper patient positioning, cuff size, and placement are still necessary; the same principles that apply to routine office BP also apply to AOBP. (See 'Patient position' above and 'Cuff size' above and 'Cuff placement' above.)
However, several aspects of performing AOBP differ from those of routine office BP:
●Patients do not necessarily need to rest for five minutes prior to having AOBP measured [61]. Several studies have shown that systolic pressure may be as much as 7 mmHg lower with AOBP following an enforced rest period compared with daytime average ambulatory BP [61,62].
●AOBP does not need to be performed more than one time during an office visit. The fact that these devices can be programmed to automatically obtain and average three or more readings satisfies the criteria for multiple consecutive measurements. Three readings are likely sufficient, no matter which AOBP device is used.