Third Annual Medical Education Day - Feinberg School of Medicine
Blood pressure measurement in primary care Frank Lefevre MD Associate Professor of Medicine Division...
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Transcript of Blood pressure measurement in primary care Frank Lefevre MD Associate Professor of Medicine Division...
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