Blood pressure measurement in primary care

Frank Lefevre MDFrank Lefevre MDAssociate Professor of MedicineAssociate Professor of Medicine

Division of General Internal Medicine, Division of General Internal Medicine,

Northwestern Feinberg School of Medicine Northwestern Feinberg School of Medicine

Rationale

Achieving optimal outcomes in the Achieving optimal outcomes in the treatment of HTN requires accurate BP treatment of HTN requires accurate BP assessmentassessment

Current practice patterns for measuring Current practice patterns for measuring BP are suboptimalBP are suboptimal

Overview

How accurate are various methods of BP measurement?How accurate are various methods of BP measurement? Office BP measurementOffice BP measurement Out of office BP measurementOut of office BP measurement

Patient self-measurementPatient self-measurement Ambulatory BP monitoringAmbulatory BP monitoring

Can the use of out of office BP measurements improve Can the use of out of office BP measurements improve outcomes?outcomes? Diagnosing HTNDiagnosing HTN Monitoring treatmentMonitoring treatment

How can BP measurement be improved?How can BP measurement be improved?

Sources of error in BP measurement

Measurement errorMeasurement error Random variabilityRandom variability White coat effectWhite coat effect

Standardized BP measurement(AHA guidelines, Circulation, 1993;88:2460)

Patient should be:Patient should be: seated in relaxed seated in relaxed

environment forenvironment for 5min 5min Legs resting on floorLegs resting on floor Back supportedBack supported No conversation No conversation Bare arm supported on table, Bare arm supported on table,

midpoint of upper arm at midpoint of upper arm at level of heartlevel of heart

Examiner technique:Examiner technique: Place cuff 1-2cm above antecubital Place cuff 1-2cm above antecubital

fossa, fossa, Inflate cuff, palpate to estimate SBPInflate cuff, palpate to estimate SBP Place bell of stethoscope over brachial Place bell of stethoscope over brachial

artery, do not wedge under cuffartery, do not wedge under cuff Inflate cuff 20-30mm above estimated Inflate cuff 20-30mm above estimated

SBPSBP Deflate at 2mm/sec, listen for Karatkov Deflate at 2mm/sec, listen for Karatkov

soundssounds Allow subject to rest for at least 30secAllow subject to rest for at least 30sec Repeat measurement and take average Repeat measurement and take average

of both measurementsof both measurements

Do MD’s 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 errorAssessed potential for measurement error

Accuracy of sphygmomanometersAccuracy of sphygmomanometers 40% off by 40% off by 4mm; 30% off by 4mm; 30% off by 10mm10mm

Physician techniquePhysician technique

Technique % following recommendations Supported arm at heart level 90% Palpation to initially assess systolic BP 38% Measurement in both arms 23% Appropriate rate of cuff deflation 18% Patient seated in recommended position 10% At least 30sec rest between BP measurements 4% Checked appropriateness of cuff size 3%

Impact of errors in technique(McAlister et al, BMJ, 2001;322:908)

FactorFactor Systolic BPSystolic BP Diastolic BPDiastolic BP

TalkingTalking 17mm Hg17mm Hg 13mm Hg13mm Hg

Exposure to coldExposure to cold 11mm Hg11mm Hg 8mm Hg8mm Hg

Ingestion of alcoholIngestion of alcohol 8mm Hg8mm Hg 8mm Hg8mm Hg

SupineSupine No effectNo effect 2-5mm Hg2-5mm Hg

Arm position above heartArm position above heart 8mm Hg/10cm 8mm Hg/10cm 8mm Hg/10cm 8mm Hg/10cm

Arm position below heartArm position below heart 8mm Hg/10cm 8mm Hg/10cm 8mm Hg/10cm 8mm Hg/10cm

Arm not supportedArm not supported 2mm Hg2mm Hg 2mm Hg2mm Hg

Cuff too smallCuff too small 3 mm Hg3 mm Hg 8mm Hg8mm Hg

Effect of random variability on the diagnosis of HTN(Mar et al, J Med Dec Mak, 1998)

Modeling studyModeling study Simulated predictive value of diagnosing mild HTN with 3 Simulated predictive value of diagnosing mild HTN with 3

measurements (office BP measure), as compared to 24 measurements (office BP measure), as compared to 24 measurements (ambulatory BP measure), accounting for measurements (ambulatory BP measure), accounting for random variabilityrandom variability

Did not consider white coat effect or measurement errorDid not consider white coat effect or measurement error

PPVPPV 3 BP measurements:3 BP measurements: 0.640.64 24 BP measurements:24 BP measurements: 0.840.84

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 BPAlerting response causing acutely elevated BP May be large; up to 40% of pts have WCE > 20/10mm HgMay be large; up to 40% of pts have WCE > 20/10mm Hg Magnitude dependent on number of office readingsMagnitude dependent on number of office readings Larger magnitude:Larger magnitude:

Taken by physicianTaken by physician Older patientsOlder patients Higher baseline pressureHigher baseline pressure

Difference in SBP readings between clinic BP and ABPM

Difference (SD) from clinic

Study

N

Daytime

Nighttime

24hr

Ironson, 1989

119

5

Jula, 1999

233

-3.8

19

2.8 Khoury, 1992

131

17

Modesti, 1994

139

9

22

12 Myers, 1995b

147

14

Narkiewicz, 1995

411

11.2

Staessen, 1999

808

21.9

Stergiou, 1998b

189

6.9

23.9

13.1 Thijs, 1996

477

21

Zachariah, 1991

126

-7

Zachariah, 1988

168

4

8

Zawadzka, 1998

410

11.5

Comparative accuracy of different methods of BP measurement

Lack of true gold standardLack of true gold standard Accuracy estimated by:Accuracy estimated by:

Predictive ability for future CV events Predictive ability for future CV events (prospective studies)(prospective studies)

degree of correlation with hypertensive end-degree of correlation with hypertensive end-organ damage (cross-sectional studies)organ damage (cross-sectional studies)

Prospective cohort studies(Perloff et al 1989:

1,079 patients with essential HTN followed for 5.5 1,079 patients with essential HTN followed for 5.5 years.years. Classified patients as ABP higher than predicted by Classified patients as ABP higher than predicted by

office BP, same, or lower than predicted:office BP, same, or lower than predicted: Patients with ABP lower than predicted had more Patients with ABP lower than predicted had more

favorable prognosisfavorable prognosis Major limitations:Major limitations:

Did not specifically evaluate patients with WC HTNDid 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 eventsFailed to consider covariates contributing to cardiac events

Prospective cohort studies (Verdecchia et al 1989)

1,187 patients with essential HTN followed for mean 1,187 patients with essential HTN followed for mean of 3.2 years.of 3.2 years. WC HTN defined as office BP >140/90 and ABP<136/87 WC HTN defined as office BP >140/90 and ABP<136/87

(men) or 131/86 (women); n=228.(men) or 131/86 (women); n=228. Compared with 205 healthy normotensive patientsCompared with 205 healthy normotensive patients

ACE/100 pt-yrsACE/100 pt-yrs True HTN:True HTN: 1.79 1.79 WC HTN:WC HTN: 0.49 0.49 Normotensive: Normotensive: 0.47 0.47

Major limitation - confounding by treatment in WC HTN Major limitation - confounding by treatment in WC HTN group.group.

Prospective cohort studies (Khattar 1998)

: Longest cohort study:: Longest cohort study: 479 patients followed for over 9 years from one center in 479 patients followed for over 9 years from one center in

UK; 126 patients with WC HTNUK; 126 patients with WC HTN rate of adverse cardiovascular events for WC HTN rate of adverse cardiovascular events for WC HTN

compared with sustained HTNcompared with sustained HTN

ACE’s/100 pt-yrsACE’s/100 pt-yrs WC HTNWC HTN 1.321.32 Sustained HTNSustained HTN 2.562.56

Major limitations:Major limitations: no comparison with normotensive groupno comparison with normotensive group confounding by treatment (82% WC pts treated)confounding by treatment (82% WC pts treated)

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

Ambulatory BP monitoring – de facto gold standard?

Limitations of ABP monitoring

No good epidemiologic benchmarks for determining No good epidemiologic benchmarks for determining treatment thresholdtreatment threshold Virtually all studies of treatment and prognosis have used Virtually all studies of treatment and prognosis have used

office BP readingsoffice BP readings One epidemiologic study of ABP/prognosis (Okhubo et al One epidemiologic study of ABP/prognosis (Okhubo et al

1998): 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 years1542 patients from one city in Japan followed for 6.2 years Ambulatory BP associated with best prognosis:Ambulatory BP associated with best prognosis:

• 120-133mmHg systolic120-133mmHg systolic• 65-78mmHg diastolic65-78mmHg diastolic

Interpretation of ABPM results(Adapted from Okhubo et al, Hyperten, 1998;32:255)

Probably normal Borderline Probably abnormal

Mean SBP

Awake <135 135-140 >140

Asleep <120 120-125 >125

24 hour <130 130-135 >135

Mean DBP

Awake <85 85-90 >90

Asleep <75 75-80 >80

24 hour <80 80-85 >85

Patient self-monitoring

Accuracy approaches that of ABPM in Accuracy approaches that of ABPM in groups of patients in research studiesgroups of patients in research studies

Accuracy/validity of measurements in Accuracy/validity of measurements in individual patient less certainindividual patient less certain

Validity may vary by whether used for Validity may vary by whether used for diagnosis of HTN vs management of known diagnosis of HTN vs management of known HTNHTN

Comparison of office, home and ambulatory BP’s

StudyStudy NN

Mean Systolic BPMean Systolic BP

Office Self ABP monitorOffice Self ABP monitor

Kleinert 1984Kleinert 1984 9393 148148 138138 131131

Flapan 1987Flapan 1987 2424 167167 151151 126126

Kenny 1987Kenny 1987 1919 156156 147147 139139

Marolf 1987Marolf 1987 3131 147147 134134 130130

Bialy 1988Bialy 1988 1515 129129 131131 130130

James 1988James 1988 1313 155155 141141 133133

O’brien 1988O’brien 1988 1818 160160 153153 148148

Mengden 1992Mengden 1992 5151 153153 147147 149149

Mancia 1995Mancia 1995 14381438 128128 119119 118118

Weighted AvgWeighted Avg 17021702 131.6131.6 122.5122.5 120.7120.7

Difference between clinic and self- measured blood pressure

(Adapted from

Mean (SD) Systolic BP

Systolic Difference

Study

N

Clinic

SMBP

Mean (SD)

P-value

Abe, 1987

100

165.5

147.8

17.7

<0.001

Jula, 1999

233

144.5

138.9

5.6

<0.001

Mengden, 1991

127

131.3

125.9

5.4

<0.01

Nielsen, 1986

122

13.0

>0.05

Stergiou, 1998b

189

142.9

137.5

5.4

<0.001

Weisser, 1994

503

130

123.1

6.9

<0.01

Difference between ABPM and self- measurement of BP

(Adapted from

ABPM

Study

N

Self-

measurement

Daytime

Nighttime

24hr Sega, 1994

1651

119

118 Stergiou, 1998b

189

137.5

136

119

129.8

Stergiou, 2000

133

138.7

139.3

How often do individual patients get inaccurate self-readings?

(Merrick et al, South Med J, 1997;90:1110

Methods:Methods: 91 volunteer patients self-91 volunteer patients self-

measured BP in the presence of measured BP in the presence of trained techniciantrained technician

Accuracy defined as systolic Accuracy defined as systolic and diastolic BP within 10mm and diastolic BP within 10mm of values recorded by of values recorded by techniciantechnician

Results:Results: 66% accurate66% accurate 34% inacurrate34% inacurrate Clinical and demographic Clinical and demographic

factors not predictive of factors not predictive of accuracyaccuracy

Performance characteristics for SBP measurement in diagnosing HTN

(Little et al, BMJ, 2002;325:254)

MeasureMeasure Sensitivity Sensitivity (%)(%)

Specificity Specificity (%)(%)

LR +LR + LR -LR -

DoctorDoctor 91.291.2 25.825.8 1.21.2 0.330.33

NurseNurse 83.383.3 41.241.2 1.41.4 0.410.41

Self – HospitalSelf – Hospital 92.792.7 50.050.0 1.91.9 0.150.15

Self- HomeSelf- Home 87.087.0 59.759.7 2.22.2 0.220.22

RCT’s comparing ABPM with office BP for monitoring HTN

Systolic Blood Pressure (mmHg)

Diastolic Blood Pressure

(mmHg)

Change from Baseline in

intervention group, net of control

Change from Baseline in

intervention group, net of control

Study

Group

Baseline

Mean (SD)

Change

P-value

Baseline Mean (SD)

Change

P-value

Control

167.6

99.5

Schrader, 2000

ABP 165.9

1

NS

100

0

NS

Control

164.4

104

Staessen, 1997

ABP 164.9

3.3

0.06

102.9

1.4

0.16

Outcomes of monitoring BP with ABPM vs office measurement

Staessen et al

419 patients with office DBP >95 randomized to follow-up 419 patients with office DBP >95 randomized to follow-up with either ABPM or office BPwith either ABPM or office BP

Medication adjusted in a stepwise fashion according to BP Medication adjusted in a stepwise fashion according to BP measurementsmeasurements

Treatment group Outcome Office BP ABPM

p-value

Final clinic BP 140/90 144/90

Final ABP 128/79 129/80

% stopping meds 7.3% 26.3% <0.001

LVM by echo 203gm 196gm 0.33

Improving BP measurement

““HTN clinic” approachHTN clinic” approach ““Out of office” approachOut of office” approach ““Individualized” approachIndividualized” approach

Improving BP measurement

““HTN clinic” approachHTN clinic” approach Dedicated personnelDedicated personnel Specific training in HTNSpecific training in HTN Standardized BP measurementStandardized BP measurement Patient educationPatient education

Improving BP measurement

““Out of office” approachOut of office” approach Use out of office measurements to guide Use out of office measurements to guide

decision-makingdecision-making Use self-measurement in patients with Use self-measurement in patients with

demonstrated accuracydemonstrated accuracy Use ABPM in others, or when validity is Use ABPM in others, or when validity is

uncertainuncertain

Improving BP measurement

Individualized approach in managing BP Individualized approach in managing BP Assess absolute risk for ACE’sAssess absolute risk for ACE’s Treat based on expected benefitTreat based on expected benefit

Absolute risk may vary markedly at any level of BPAbsolute risk may vary markedly at any level of BP Expected benefit closely related to absolute riskExpected benefit closely related to absolute risk RRR of treatment will be same regardless of RRR of treatment will be same regardless of

whether BP measure is precisewhether BP measure is precise

Conclusions

Measurement of BP in the primary care office is Measurement of BP in the primary care office is highly prone to errorhighly prone to error

Out of office BP measurements can be more Out of office BP measurements can be more accurate than office BP’saccurate than office BP’s

Lack of strong evidence demonstrating an Lack of strong evidence demonstrating an improvement in outcomes associated with OOO-improvement in outcomes associated with OOO-BP readingsBP readings

Multiple potential areas for improvement in BP Multiple potential areas for improvement in BP assessmentassessment