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Blood pressure measurement in primary care Frank Lefevre MD Associate Professor of Medicine Division of General Internal Medicine, Northwestern Feinberg.

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Presentation on theme: "Blood pressure measurement in primary care Frank Lefevre MD Associate Professor of Medicine Division of General Internal Medicine, Northwestern Feinberg."— Presentation transcript:

1 Blood pressure measurement in primary care Frank Lefevre MD Associate Professor of Medicine Division of General Internal Medicine, Northwestern Feinberg School of Medicine

2 Rationale Achieving optimal outcomes in the treatment of HTN requires accurate BP assessment Achieving optimal outcomes in the treatment of HTN requires accurate BP assessment Current practice patterns for measuring BP are suboptimal Current practice patterns for measuring BP are suboptimal

3 Overview How accurate are various methods of BP measurement? How accurate are various methods of BP measurement? Office BP measurement Office BP measurement Out of office BP measurement Out of office BP measurement Patient self-measurement Patient self-measurement Ambulatory BP monitoring Ambulatory BP monitoring Can the use of out of office BP measurements improve outcomes? Can the use of out of office BP measurements improve outcomes? Diagnosing HTN Diagnosing HTN Monitoring treatment Monitoring treatment How can BP measurement be improved? How can BP measurement be improved?

4 Sources of error in BP measurement Measurement error Measurement error Random variability Random variability White coat effect White coat effect

5 Standardized BP measurement (AHA guidelines, Circulation, 1993;88:2460) Patient should be: seated in relaxed environment for 5min seated in relaxed environment for 5min Legs resting on floor Legs resting on floor Back supported Back supported No conversation No conversation Bare arm supported on table, midpoint of upper arm at level of heart Bare arm supported on table, midpoint of upper arm at level of heart Examiner technique: Place cuff 1-2cm above antecubital fossa, Inflate cuff, palpate to estimate SBP Place bell of stethoscope over brachial artery, do not wedge under cuff Inflate cuff 20-30mm above estimated SBP Deflate at 2mm/sec, listen for Karatkov sounds Allow subject to rest for at least 30sec Repeat measurement and take average of both measurements

6 Do MDs follow standardized approach? (McKay et al, J Hum Hyper, 1990;4:639) Observation of 114 primary care physicians Observation of 114 primary care physicians Assessed potential for measurement error Assessed potential for measurement error Accuracy of sphygmomanometers Accuracy of sphygmomanometers 40% off by 4mm; 30% off by 10mm 40% off by 4mm; 30% off by 10mm Physician technique Physician technique

7 Impact of errors in technique (McAlister et al, BMJ, 2001;322:908) Factor Systolic BP Diastolic BP Talking 17mm Hg 17mm Hg 13mm Hg 13mm Hg Exposure to cold 11mm Hg 11mm Hg 8mm Hg 8mm Hg Ingestion of alcohol 8mm Hg 8mm Hg Supine No effect 2-5mm Hg 2-5mm Hg Arm position above heart 8mm Hg/10cm 8mm Hg/10cm Arm position below heart 8mm Hg/10cm 8mm Hg/10cm Arm not supported 2mm Hg 2mm Hg Cuff too small 3 mm Hg 3 mm Hg 8mm Hg 8mm Hg

8 Effect of random variability on the diagnosis of HTN (Mar et al, J Med Dec Mak, 1998) Modeling study Modeling study Simulated predictive value of diagnosing mild HTN with 3 measurements (office BP measure), as compared to 24 measurements (ambulatory BP measure), accounting for random variability Simulated predictive value of diagnosing mild HTN with 3 measurements (office BP measure), as compared to 24 measurements (ambulatory BP measure), accounting for random variability Did not consider white coat effect or measurement error Did not consider white coat effect or measurement errorPPV 3 BP measurements: BP measurements: BP measurements: BP measurements:0.84

9 The white coat effect (WCE) Generally defined as: (office BP - out of office BP) Generally defined as: (office BP - out of office BP) Alerting response causing acutely elevated BP Alerting response causing acutely elevated BP May be large; up to 40% of pts have WCE > 20/10mm Hg May be large; up to 40% of pts have WCE > 20/10mm Hg Magnitude dependent on number of office readings Magnitude dependent on number of office readings Larger magnitude: Larger magnitude: Taken by physician Taken by physician Older patients Older patients Higher baseline pressure Higher baseline pressure

10 Difference in SBP readings between clinic BP and ABPM

11 Comparative accuracy of different methods of BP measurement Lack of true gold standard Lack of true gold standard Accuracy estimated by: Accuracy estimated by: Predictive ability for future CV events (prospective studies) Predictive ability for future CV events (prospective studies) degree of correlation with hypertensive end- organ damage (cross-sectional studies) degree of correlation with hypertensive end- organ damage (cross-sectional studies)

12 Prospective cohort studies (Perloff et al 1989: 1,079 patients with essential HTN followed for 5.5 years. 1,079 patients with essential HTN followed for 5.5 years. Classified patients as ABP higher than predicted by office BP, same, or lower than predicted: Classified patients as ABP higher than predicted by office BP, same, or lower than predicted: Patients with ABP lower than predicted had more favorable prognosis Patients with ABP lower than predicted had more favorable prognosis Major limitations: Major limitations: Did not specifically evaluate patients with WC HTN Did not specifically evaluate patients with WC HTN Confounding by treatment of patients with WC HTN Confounding by treatment of patients with WC HTN Failed to consider covariates contributing to cardiac events Failed to consider covariates contributing to cardiac events

13 Prospective cohort studies (Verdecchia et al 1989) 1,187 patients with essential HTN followed for mean of 3.2 years. 1,187 patients with essential HTN followed for mean of 3.2 years. WC HTN defined as office BP >140/90 and ABP 140/90 and ABP<136/87 (men) or 131/86 (women); n=228. Compared with 205 healthy normotensive patients Compared with 205 healthy normotensive patients ACE/100 pt-yrs True HTN: 1.79 True HTN: 1.79 WC HTN: 0.49 WC HTN: 0.49 Normotensive: 0.47 Normotensive: 0.47 Major limitation - confounding by treatment in WC HTN group. Major limitation - confounding by treatment in WC HTN group.

14 Prospective cohort studies (Khattar 1998) : Longest cohort study: : Longest cohort study: 479 patients followed for over 9 years from one center in UK; 126 patients with WC HTN 479 patients followed for over 9 years from one center in UK; 126 patients with WC HTN rate of adverse cardiovascular events for WC HTN compared with sustained HTN rate of adverse cardiovascular events for WC HTN compared with sustained HTN ACEs/100 pt-yrs WC HTN1.32 WC HTN1.32 Sustained HTN2.56 Sustained HTN2.56 Major limitations: Major limitations: no comparison with normotensive group no comparison with normotensive group confounding by treatment (82% WC pts treated) confounding by treatment (82% WC pts treated)

15 Cross-sectional studies Numerous studies comparing accuracy of ABP and office BP by comparing correlation with end- organ damage (LVM) Meta-analysis of 21 studies (Fagard et al 1995): Correlation with LVM Ambulatory BP: r = 0.50 Office BP:r = 0.35

16 Ambulatory BP monitoring – de facto gold standard?

17 Limitations of ABP monitoring No good epidemiologic benchmarks for determining treatment threshold No good epidemiologic benchmarks for determining treatment threshold Virtually all studies of treatment and prognosis have used office BP readings Virtually all studies of treatment and prognosis have used office BP readings One epidemiologic study of ABP/prognosis (Okhubo et al 1998): One epidemiologic study of ABP/prognosis (Okhubo et al 1998): Population based study of ABP and prognosis Population based study of ABP and prognosis 1542 patients from one city in Japan followed for 6.2 years 1542 patients from one city in Japan followed for 6.2 years Ambulatory BP associated with best prognosis: Ambulatory BP associated with best prognosis: mmHg systolic mmHg systolic 65-78mmHg diastolic65-78mmHg diastolic

18 Interpretation of ABPM results (Adapted from Okhubo et al, Hyperten, 1998;32:255) Probably normalBorderlineProbably abnormal Mean SBP Awake< >140 Asleep< > hour< >135 Mean DBP Awake< >90 Asleep< >80 24 hour< >85

19 Patient self-monitoring Accuracy approaches that of ABPM in groups of patients in research studies Accuracy approaches that of ABPM in groups of patients in research studies Accuracy/validity of measurements in individual patient less certain Accuracy/validity of measurements in individual patient less certain Validity may vary by whether used for diagnosis of HTN vs management of known HTN Validity may vary by whether used for diagnosis of HTN vs management of known HTN

20 Comparison of office, home and ambulatory BPs StudyN Mean Systolic BP Office Self ABP monitor Office Self ABP monitor Kleinert Flapan Kenny Marolf Bialy James Obrien Mengden Mancia Weighted Avg

21 Difference between clinic and self- measured blood pressure (Adapted from

22 Difference between ABPM and self- measurement of BP (Adapted from

23 How often do individual patients get inaccurate self-readings? (Merrick et al, South Med J, 1997;90:1110 Methods: Methods: 91 volunteer patients self- measured BP in the presence of trained technician 91 volunteer patients self- measured BP in the presence of trained technician Accuracy defined as systolic and diastolic BP within 10mm of values recorded by technician Accuracy defined as systolic and diastolic BP within 10mm of values recorded by technician Results: 66% accurate 34% inacurrate Clinical and demographic factors not predictive of accuracy

24 Performance characteristics for SBP measurement in diagnosing HTN (Little et al, BMJ, 2002;325:254) Measure Sensitivity (%) Specificity (%) LR + LR - Doctor Nurse Self – Hospital Self- Home

25 RCTs comparing ABPM with office BP for monitoring HTN

26 Outcomes of monitoring BP with ABPM vs office measurement Staessen et al 419 patients with office DBP >95 randomized to follow-up with either ABPM or office BP 419 patients with office DBP >95 randomized to follow-up with either ABPM or office BP Medication adjusted in a stepwise fashion according to BP measurements Medication adjusted in a stepwise fashion according to BP measurements

27 Improving BP measurement HTN clinic approach HTN clinic approach Out of office approach Out of office approach Individualized approach Individualized approach

28 Improving BP measurement HTN clinic approach HTN clinic approach Dedicated personnel Dedicated personnel Specific training in HTN Specific training in HTN Standardized BP measurement Standardized BP measurement Patient education Patient education

29 Improving BP measurement Out of office approach Out of office approach Use out of office measurements to guide decision-making Use out of office measurements to guide decision-making Use self-measurement in patients with demonstrated accuracy Use self-measurement in patients with demonstrated accuracy Use ABPM in others, or when validity is uncertain Use ABPM in others, or when validity is uncertain

30 Improving BP measurement Individualized approach in managing BP Individualized approach in managing BP Assess absolute risk for ACEs Assess absolute risk for ACEs Treat based on expected benefit Treat based on expected benefit Absolute risk may vary markedly at any level of BP Absolute risk may vary markedly at any level of BP Expected benefit closely related to absolute risk Expected benefit closely related to absolute risk RRR of treatment will be same regardless of whether BP measure is precise RRR of treatment will be same regardless of whether BP measure is precise

31 Conclusions Measurement of BP in the primary care office is highly prone to error Measurement of BP in the primary care office is highly prone to error Out of office BP measurements can be more accurate than office BPs Out of office BP measurements can be more accurate than office BPs Lack of strong evidence demonstrating an improvement in outcomes associated with OOO- BP readings Lack of strong evidence demonstrating an improvement in outcomes associated with OOO- BP readings Multiple potential areas for improvement in BP assessment Multiple potential areas for improvement in BP assessment


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