A meta‐analysis that helps clarify the use of automated office blood pressure in clinical practice

Meta-analyses designed to explore clinical issues are intrinsically open to discussion since their conclusions can be affected by the articles which are chosen for inclusion in the analyses. There is often no simple right or wrong, but rather the issues are usually of selection criteria and interpretation of data. An interesting and important example is the recent meta-analysis published in this Journal by Kollias et al,1 which has addressed several aspects of automated office blood pressure (AOBP) measurement. The authors performed a systematic review and meta-analysis of unattended vs attended AOBP, the only difference being the presence or absence of office staff while BP was being recorded. After analyzing data from 10 studies, they concluded, with several provisos, that the 2 techniques provided similar BP readings. Although the ultimate validity of their conclusion remains uncertain, their findings are useful in clarifying several aspects of office BP measurement which may not be widely understood. Automated office blood pressure has been defined in numerous publications as multiple office BP readings recorded using a fully automated oscillometric sphygmomanometer with the patient resting alone in a quiet place, such as an examining room. The rationale underlying AOBP is that having the patient alone will eliminate many of the factors contributing to a white coat effect (WCE) in patients with apparent hypertension. When this rationale was first tested in 19972 using a semi-automated oscillometric sphygmomanometer, the mean systolic BP obtained from duplicate, patient-activated readings was 12 mm Hg higher than the mean awake ambulatory (A) BP, a recognized standard for diagnosing hypertension. It was not until the development of fully automated, oscillometric sphygmomanometers such as the BpTRU and Omron 907, capable of recording multiple readings with a single activation, that it became possible to eliminate most human involvement in the process of recording office BP. The net result, as confirmed in a recent meta-analysis,3 is that mean AOBP in hypertensive patients is similar to the awake ambulatory (A) BP, with no evidence of a WCE. In 4 of the 10 studies4-7 classified by Kollias et al as being AOBP, the attended vs unattended readings were recorded using semi-automated, oscillometric sphygmomanometers, with the mean readings being similar. However, in 35-7 of these studies in which home BP, another out-of-office standard used to diagnose hypertension, was also recorded, the mean patient-activated “AOBP” reading was 6.9/2.9 mm Hg higher than self-measured BP in the home. In contrast, a proper mean AOBP in hypertensive patients recorded with a fully automated sphygmomanometer should have been similar to the out-of-office BP. This aspect of the meta-analysis is important in that it underscores the importance of using fully automated sphygmomanometers which have been specifically designed for professional use in the office to record AOBP in order to eliminate any WCE in patients suspected of being hypertensive. Another feature of the meta-analysis which warrants further attention is the level of mean office BP in the patient population. The authors correctly noted that there was a trend to a higher attended “AOBP” than awake ABP in the studies with a higher mean office BP. This finding is extremely important when it comes to evaluating the relationship between office BP and awake ABP in research studies. Since 1993, it has been apparent that office BP in the normotensive range, such as a systolic BP < 130 mm Hg, is generally lower in research studies than the awake ABP.5 In other words, there is no WCE when office BP in a research study is quite normal. A review8 of studies examining the relationship between awake ABP and a normal office BP, recorded using several different techniques, including AOBP,3 has shown that mean office BP is invariably lower than awake ABP, regardless of how BP is recorded. Thus, the equivalence of attended and unattended AOBP in 3 of the studies9-11 in the present meta-analysis in which subjects had a mean office systolic BP in research settings < 130 mm Hg is likely valid, in that having the patient alone would not be expected to lower mean BP by reducing WCE. However, the relationship between office BP < 130 mm Hg and awake systolic ABP may be somewhat different when it comes to target BP recorded in routine clinical practice. Analysis of data from the Spanish Ambulatory BP Monitoring (ABPM) Registry12 in which office BP was recorded in duplicate by physicians and nurses in primary care using oscillometric sphygmomanometers showed that the mean office BP was still slightly higher than the awake ABP in 1607 treated hypertensive patients, with systolic BP readings in the range of 120-129 mm Hg being 125/78 mm Hg compared to an awake ABP of 123/74 mm Hg. In contrast, there was still a noticeable WCE for systolic BP readings of 130-139 mm Hg, with mean office BP 3421 subjects being 135/83 compared to an awake ABP of 127/76 mm Hg (A. de la Sierra, personal communication). Thus, the WCE seen at higher BP values may be reduced, but not eliminated entirely, at systolic BP readings 120-129 mm Hg when BP is recorded with oscillometric devices in the presence of office staff. However, in the Spanish ABPM Registry, awake ABP did become greater than the office BP in patients with an office systolic BP < 120 mm Hg. There are no similar data available comparing manual office BP with the awake ABP in clinical practice. Finally, the 3 remaining studies analyzed by Kollias et al13-15 addressed the question: “Is a proper AOBP reading performed in the presence of a physician or nurse similar to a BP obtained with the patient alone?” In these studies, which were specifically undertaken to show equivalence between the methods, the overall mean attended systolic AOBP was 4.3 mm Hg higher than the mean unattended AOBP. In comparison, in 9 other studies3 without this specific objective, a more usual research-quality mean systolic BP was 7 mm Hg higher than the AOBP, whereas in 9 studies3 in routine clinical practice, office BP was 14 mm Hg higher than AOBP. The answer to the above question of Kollias et al would seem to be: “It depends on how carefully office BP is measured.” Kollias et al acknowledged this caveat, but still concluded that, even though unattended AOBP may be more accurate, it cannot be implemented “in all primary care settings” because it requires additional space and time to obtain the BP. They recommended “national protocols…for widespread implementation of standardized office BP measurements across primary care settings”, presumably to ensure that an attended oscillometric office BP follows proper measurement guidelines, especially no conversation. But, isn't this what organizations such as the American Heart Association have been promoting for decades—guidelines for proper BP measurement? The reality of current clinical practice is that the mean manual or oscillometric office systolic BP is about 14 mm Hg higher than either the mean awake ABP or AOBP.3 Even when duplicate oscillometric office readings were recorded in 27 211 treated hypertensive (systolic BP ≥ 140 mm Hg) patients in primary care in the Spanish ABPM Registry,12 the mean systolic BP was 25 mm Hg higher than the mean awake BP. There is absolutely no evidence to support the expectation that more “national protocols” will lead to office readings which are as accurate as a proper AOBP in identifying patients with possible hypertension. In contrast, in untreated patients in clinical practice, mean systolic AOBP at 135 and 130 mm Hg was only 0.7 and 2.0 mm Hg, respectively,16 different from the awake ABP, indicating that AOBP is already consistent with the new BP measurement guidelines when it comes to diagnosing hypertension in the office. There may be other, non-scientific, reasons why critics of AOBP maintain that it is not feasible for physicians’ offices, even though it provides superior readings compared to other BP measurement techniques. AOBP requires the purchase of special equipment, a fully automated, oscillometric sphygmomanometer designed for professional use. AOBP also requires a place for the patient to be alone while the readings are obtained, the same place where the patient is supposed to rest for 5 minutes before a conventional BP reading. However, AOBP does NOT require more time than a conventional BP, unless the physician or nurse takes 2-3 readings without the 5 minutes of antecedent rest. In fact, less time is required for AOBP, since office staff can perform other tasks while the BP is being recorded automatically. The feasibility of introducing AOBP into primary care has already been demonstrated in Canada, where more than 50% of family physicians use AOBP in their practice.17 Leaving feasibility aside, I suspect that Kollias et al would agree that AOBP is the best method for hypertension screening, with a diagnosis to be confirmed by ABPM or home BP. Out-of-office BP readings may also be necessary to confirm that target BP has been achieved. AOBP, ABPM and home BP are complementary, although each involves a change from the traditional way of managing patients with hypertension. The new approach is consistent with the Hypertension Canada guidelines18 and has recently been included in an evidence-based Statement on BP Measurement from the American Heart Association19 in which AOBP is the “preferred” method for office BP, with the diagnosis of hypertension to be confirmed using ABPM, or alternatively home BP, if ABPM is not feasible. It is now time to follow the evidence and not to rely on the expectation that the quality of BP readings recorded by office staff will somehow improve with better educational programs. No conflicts of interest to disclose.

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