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Blood pressure measurement in primary care

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Presentation on theme: "Blood pressure measurement in primary care"— 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 Current practice patterns for measuring BP are suboptimal

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

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

5 Standardized BP measurement (AHA guidelines, Circulation, 1993;88:2460)
Patient should be: seated in relaxed environment for 5min Legs resting on floor Back supported No conversation 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 MD’s follow standardized approach
Do MD’s follow standardized approach? (McKay et al, J Hum Hyper, 1990;4:639) Observation of 114 primary care physicians Assessed potential for measurement error Accuracy of sphygmomanometers 40% off by  4mm; 30% off by 10mm Physician technique

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

8 Effect of random variability on the diagnosis of HTN (Mar et al, J Med Dec Mak, 1998)
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 Did not consider white coat effect or measurement error PPV 3 BP measurements: 24 BP measurements:

9 The “white coat effect” (WCE)
Generally defined as: (office BP - out of office BP) Alerting response causing acutely elevated BP May be large; up to 40% of pts have WCE > 20/10mm Hg Magnitude dependent on number of office readings Larger magnitude: Taken by physician Older patients 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 Accuracy estimated by: Predictive ability for future CV events (prospective 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. 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 Major limitations: Did not specifically evaluate patients with WC HTN Confounding by treatment of patients with “WC HTN” 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. WC HTN defined as office BP >140/90 and ABP<136/87 (men) or 131/86 (women); n=228. Compared with 205 healthy normotensive patients ACE/100 pt-yrs True HTN: WC HTN: Normotensive: Major limitation - confounding by treatment in WC HTN group.

14 Prospective cohort studies (Khattar 1998)
: Longest cohort study: 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 ACE’s/100 pt-yrs WC HTN Sustained HTN Major limitations: no comparison with normotensive group 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 Virtually all studies of treatment and prognosis have used office BP readings One epidemiologic study of ABP/prognosis (Okhubo et al 1998): Population based study of ABP and prognosis 1542 patients from one city in Japan followed for 6.2 years Ambulatory BP associated with best prognosis: mmHg systolic 65-78mmHg diastolic

18 Interpretation of ABPM results (Adapted from Okhubo et al, Hyperten, 1998;32:255)
Probably normal Borderline Probably abnormal Mean SBP Awake <135 >140 Asleep <120 >125 24 hour <130 >135 Mean DBP <85 85-90 >90 <75 75-80 >80 <80 80-85 >85

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

20 Comparison of office, home and ambulatory BP’s
Study N Mean Systolic BP Office Self ABP monitor Kleinert 1984 93 148 138 131 Flapan 1987 24 167 151 126 Kenny 1987 19 156 147 139 Marolf 1987 31 134 130 Bialy 1988 15 129 James 1988 13 155 141 133 O’brien 1988 18 160 153 Mengden 1992 51 149 Mancia 1995 1438 128 119 118 Weighted Avg 1702 131.6 122.5 120.7

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
How often do individual patients get inaccurate self-readings? (Merrick et al, South Med J, 1997;90:1110 Methods: 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 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)
Sensitivity (%) Specificity (%) LR + LR - Doctor 91.2 25.8 1.2 0.33 Nurse 83.3 41.2 1.4 0.41 Self – Hospital 92.7 50.0 1.9 0.15 Self- Home 87.0 59.7 2.2 0.22

25 RCT’s 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 Medication adjusted in a stepwise fashion according to BP measurements

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

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

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

30 Improving BP measurement
Individualized approach in managing BP Assess absolute risk for ACE’s Treat based on expected benefit Absolute risk may vary markedly at any level of BP Expected benefit closely related to absolute risk 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 Out of office BP measurements can be more accurate than office BP’s Lack of strong evidence demonstrating an improvement in outcomes associated with OOO-BP readings Multiple potential areas for improvement in BP assessment

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