Accuracy of four indirect methods of blood pressure measurement… · 2017. 8. 26. · IBP and intraarterial blood pressure (ABP) [1-4], and few studies have closely evaluated inter-patient

ACCURACY OF FOUR INDIRECT METHODS OF DLOOD PRESSURE MEASUREMEHT, WiTH HEMODYNAMIC CORRELATIONS Glenn P. Gravlee, MD, and Joni K. Brockschmidt, MS

From the Departments of Anesthesia and Public Health Sciences, Bowman Gray School of Medicine of Wake Forest University, Win- ston-Salem, NC.

Received Dec 9, 1989, and in revised form Dec 28. Accepted for publication Jan 8, 1990.

Address correspondence to Dr Gravlee, Dept of Anesthesia, Bowman Gray School of Medicine, 300 S Hawthorne Rd, Winston-Salem, NC 27103.

Gravlee GP, Brockschmidt JK. Accuracy of four indirect methods of blood pressure measurement, with hemodynamic correlations.

J Clin Monit 1990;6:284-298

AGSTRACT. In 38 adults undergoing cardiac surgery, 4 indirect blood pressure techniques were compared with brachial arterial blood pressure at predetermined intervals before and after cardiopulmonary bypass. Indirect blood pressure measurement techniques included automated osciliometry, manual auscultation, visual onset o f oscillation (flicker) and return-to- flow methods. Hemodynamic measurements or calculations included heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect and intraarterial blood pressure values were compared by simple linear regression by patient and measurement period. Measurement errors (arterial minus indirect blood pressure) were calculated, and stepwise regression assessed the relationship between measurement error and heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect to intraarterial blood pressure correlation coefficients varied over time, with the strongest correlations often occurring at the first and last measurement periods (preinduction and 60 minutes after cardiopulmonary bypass), particularly for systolic blood pressure. Within-patient correlations between indirect and arterial blood pressure varied widely-- they were consistently high or low in some patients. In other patients, correlations were especially weak with a particular indirect blood pressure method for systolic, mean, or diastolic blood pressure; in some cases indirect blood pressure was inadequate for clinical diagnosis o f acute blood pressure changes or trends. The mean correlations between indirect and direct blood pressure values were, for systolic blood pressure: 0.69 for oscillometry, 0.77 for auscultation, 0.73 for flicker, and 0.74 for return-to-flow; for mean blood pressure: 0.70 for oscillometry and 0.73 for auscultation; and for diastolic blood pressure: 0.73 for oscillometry and 0.69 for auscultation. The mean measurement errors (arterial minus indirect values) for the individual indirect blood pressure methods were, for systolic: 0 mm Hg for oscillometry, 9 mm Hg for auscultation, - 5 m m Hg for flicker, 7 m m Hg for return-to-flow; for mean: - 6 mm Hg for oscillometry, and - 3 m m Hg for auscultation; and for diastolic: - 9 m m Hg for oscillometry and - 8 mm Hg for auscultation. Mean measurement error for systolic blood pressure was thus least with automated oscillometry and greatest with manual auscultation, while standard deviations ranging from 9 to 15 m m Hg confirmed the highly variable nature o f single indirect blood pressure measurements. Except for oscillometric diastolic blood pressure, a combination of systemic hemodynamics (heart rate, stroke volume index, systemic vascular resistance index, and cardiac index) correlated with each indirect blood pressure measurement error, which suggests that particular numeric ranges of these variables minimize measurement error. This study demonstrates that striking variability occurs in the relationship between indirect and arterial blood pressure measurements, and that the systemic hemodynamic state influences accuracy of indirect blood pressure measurements. When the reproducibility of repeated indirect blood pressure measurements appears unsatisfactory or inconsistent with other clinical observations, clinicians may fred that an alternative indirect blood pressure method is a better choice. O f the methods tested, no single indirect blood pressure technique showed precision superior to the others, but two methods yielded data only for systolic pressure. These findings lend support to intraarterial blood pressure measure-

284 Copyright �9 1990 by Little, Brown and Company

Gravlee and Brockschmidt: Four Indirect Methods of Blood Pressure Measurement 285

ment in conditions of hemodynamic variability, and suggest the theoretical benefits of continuous indirect blood pressure measurements.

KEY WORM. Blood pressure: measurement. Monitoring: blood pressure, arterial. Measurement techniques: oscillometry.

Anesthesiologists and intensive care specialists fre- quently use indirect blood pressure (IBP) measurements to guide clinical decisions, yet little information exists relating systemic hemodynamics to differences between IBP and intraarterial blood pressure (ABP) [1-4], and few studies have closely evaluated inter-patient or time- related variability in the relationship between IBP and ABP [5-11]. Commonly used IBP methods include automated oscillometry and auscultation. When using auscultatory blood pressures with an aneroid manometer, the first visible needle oscillation during cuff deflation has been used to confirm systolic blood pressure (SBP) [12], particularly when Korotkoff sounds prove difficult to auscultate. For patients with indwelling arterial catheters, skepticism about directly recorded SBP values may lead to a return-to-flow measurement, which represents a direct blood pressure method as- sisted by a cuffand manometer [12]. These 4 commonly available IBP methods were selected for comparison with ABP.

The present investigation further defines the relationship between IBP and ABP using single IBP measurements to approximate conditions under which clinicians commonly monitor blood pressure. Cardiac surgical patients were selected for this comparison because they experience a broad range of hemodynamic alterations. Recent studies have shown substantial variation in the IBP measurement error in these patients [5,6]. Com- mon use of pulmonary artery catheters in these patients also affords an opportunity to investigate possible con- tributions of systemic hemodynamics to differences between IBP and ABP.

METHOOS AND MATERIALS

After obtaining protocol approval from the institutional human studies committee and informed consent from each patient, 38 adults undergoing cardiac surgery were studied. Table 1 lists patient characteristics. On the day preceding surgery, auscultatory blood pressure was measured twice on each arm using standardized technique [13], excluding patients with a right-to-left mean systolic pressure difference exceeding 5 mm Hg. Patients with atrial fibrillation or frequent ectopic beats were

Table 1. Preoperative Patient Characteristics

Characteristic Mean +4 SD Range

Age (yr) Height (cm) Weight (kg) Body surface area (m 2) Preoperative blood pres-

sure (mm Hg) Systolic 128 + 22 Diastolic 78 + 11

Ejection fraction 0.65 + 0.11 Sex (No.)

Male 32 Female 6

Procedure (No.) Coronary artery bypass 32

grafting Valve 6

Treated hypertension 9 (No.)

55 + 13 19-80 174 +_ 13 113-188

82.6 + 13.1 54-107 1.99 + 0.19 1.52-2.27

100-210 50-100

0.39-0.82

excluded, as were patients with obese upper arms. Di- rect ABP and four IBP methods were measured at 8 intervals: before and after anesthetic induction (times 1 and 2); after sternotomy (time 3); and 5, 10, 20, 30, and 60 minutes after separation from cardiopulmonary bypass (times 4 to 8). Following premedication with lorazepam and morphine, a 5-cm 20-gauge Teflon (An- giocath, Becton Dickinson, Sandy, UT) catheter was percutaneously placed in the brachial artery, alternating between the left and right sides. A cuff was placed on each upper arm using an inflatable cuffwith bladder size conforming to American Heart Association guidelines [13]. Anesthesia consisted of fentanyl, diazepam, and pancuronium, with supplemental enflurane in some patients. Inotropes, vasopressors, and vasodilators were administered according to the clinical judgment of the anesthesiologist (G. P. G.).

Brachial arterial pressure was measured with a Gould P50 (Spectramed, Oxnard, CA) strain gauge connected serially to a Hewlett-Packard (Waltham, MA) 8805C amplifier and 7754A thermal recorder. A 76-cm length of Gould high-pressure tubing (internal diameter, 1.60 + 0.08 mm) and two three-way stopcocks separated the arterial catheter and the strain gauge. This system was statically calibrated to a mercury standard at 0, 50, 100, 150, and 200 mm Hg for accuracy and hysteresis, cor- recting or excluding any system with an error exceeding 2 mm Hg (the resolution limit of the recordings) at any level. The fast flush method [14] determined dynamic response, rejecting systems with a resonant frequency below 12.5 Hz or a damping coefficient below 0.2

286 Journal of Clinical Monitoring Vol 6 No 40aober 1990

[15,16]. Static and dynamic calibration was performed before anesthetic induction and during cardiopulmonary bypass (mean resonant frequency, 20 _+ 6 [SD] Hz, and damping coefficient, 0.27 __+ 0.05). Arterial SBP and diastolic blood pressure (DBP) were defined as the peak and nadir, respectively, of recorded pulse waves at mid-exhalation, taking the average of ABP measurements before and after an IBP measurement set. Mean intraarterial pressure (MBP) was determined by elec- tronically integrating and averaging the area under the pressure curves taken from the strip-chart recordings, also at midexhalation. Digital values were transcribed manually from the recordings by one observer (G. P. G.) several weeks after the operation, without simultaneous observation of the previously recorded IBPs.

Four IBP measurements were made at each interval: automated oscillometry (Dinamap 845, Critikon, Tampa, FL), auscultation, flicker onset, and return-to- flow. A pilot study determined that the oscillometric pressures would be measured on the right arm, while the other IBPs would use the left arm. This combination afforded access to the abducted left arm if stethoscope repositioning were required. The right arm was rou- tinely tucked alongside the patient and the blood pressure cuff was shielded from the surgeon by a curved metal baffle. For auscultatory blood pressures, Korot- koff sounds were detected by a rubber stethoscope (Dupaco Dyasyst, Bay Medical Inc, St. Petersburg, FL) designed to conform to the curvature of the arm while remaining under the cuff. This was centered over the point of maximal brachial artery pulsation. When the arterial catheter was placed in the left brachial artery, care was taken to ensure that the tape securing the catheter did not overlap the acoustic bell of the stethoscope. The cuff was inflated to approximately 30 mm Hg above the digitally displayed arterial SBP and deflated at 2 to 3 mm Hg/s, defining auscultatory SBP and DBP as the onset (phase I) and cessation (phase V) of Korotkoff sounds, respectively [13]. Auscultatory MBP was calculated from auscultatory SBP and DBP as follows: MBP = ([SBP - DBP]/3) + DBP. Flicker SBP was recorded on a separate inflation-deflation cycle of the same cuff, and was defined as the onset of visible needle oscillation in the aneroid manometer (Tycos, Sybron Corp, Rochester, NY) as the cuff was deflated [12]. Return-to-flow blood pressure was also taken from a separate inflation-deflation cycle and was defined as the aneroid manometer pressure during cuff deflation at which visible pulsatility reappeared on the arterial trac- ing viewed on the oscilloscope screen. The Dinamap IBP algorithm has been previously described [11]. Ef- forts were made to avoid tape overlap with the Di- namap cuff bladder when the arterial catheter was

located in the right brachial artery. The automated oscillometric SBP, DBP, and MBP readings were taken from the digital display of one of two Dinamap 845 devices, both of which were statically calibrated to a mercury standard at least every 2 weeks during the study.

When the brachial arterial catheter was located in the right arm, return-to-flow pressures were taken from a left radial artery catheter placed for a separate study [17]. Statistical comparison (t test) of mean errors revealed no difference between radial and brachial artery return-to- flow SBPs. One of two aneroid manometers was used for auscultatory, flicker, and return-to-flow blood pressures; both were calibrated to a mercury standard at least weekly during the study. The order of auscultatory, flicker, and return-to-flow blood pressures was varied, with the first method commencing immediately after manually triggering a Dinamap blood pressure.

Each patient was also monitored by an electrocardio- graph and a pulmonary artery catheter (Baxter Amer- ican Edwards, Santa Ana, CA), providing measurements of heart rate (HR), cardiac output (CO), and right atrial pressure (RAP) used for subsequent hemodynamic calculations. A full set of hemodynamic measurements immediately preceded each set of blood pressure measurements. RAP was taken at end-exhalation from a strip-chart recording of an arithmetic mean. Du- plicate thermodilution cardiac outputs were performed using iced injectate with end-expiratory injections. Standard formulas calculated cardiac index (CI), stroke volume index (SVI), and systemic vascular resistance index (SVRI). Upon completing the HR, CO, and RAP measurements, ABP was recorded for at least one complete ventilatory cycle at a paper speed of 25 mm/s, then recorded at 10 mm/s during IBP measurement and for at least 10 seconds after completing a set of IBP measurements. Intraarterial MBPs were also recorded over one or more ventilator cycles before and after IBP measurements. A measurement set was repeated if the arterial SBP changed by 5 mm Hg (at the same point in the respiratory cycle) or more during the IBP measurements, which lasted 90 to 120 seconds. The latter information could not be obtained when both cuffs were inflated simultaneously. Acceptable ABP stability was always obtained by the first or second repetition. All IBP measurements were taken by the same observer (G. P. G.), whose anesthetic supervisory role precluded blinding to ABP.

Variations over time Jn ABPs, HR, CI, SVRI, SVI, and RAP were assessed by analysis of variance. DBP and IBP measurements were compared by simple linear regression for each measurement period. Associations were considered statistically significant if the regression


Table 2. Hemodynamics by Time of MeasuremenP

Time b Hemodynamic Variable 1 2 3 4 5 6 7 8

Heart rate 69 - 18 66 • 12 70 • 14 94 • 13 94 • 13 94 • 12 96 • 13 96 _ 14 (beats/rain)

Brachial intraarterial pressure (mm Hg)

Systolic 131 • 22 115 • 17 119 • 19 110 • 23 115 • 21 119 • 15 12"J _ 15 123 _-!- 23 Mean 86 • 14 78 • 9 81 • 13 78 • 13 81 • 14 85 • 12 88 • 11 88 _+ 16 Diastolic 65 • 10 61 • 8 64 • 10 62 • 10 64 • 11 69 • 10 72 • 11 72 • 12

Cardiac index 2.79 -2_ 0.71 2.45 • 0.51 2.61 • 0.70 3.11 • 0.66 2.99 • 0.66 2.92 +_ 0.71 2.72 • 0.75 2.52 • 0.62 (L - rain - m 2)

Systemic 2,270 • 650 2,320 • 620 2,370 + 20 1,790 • 600 1,950 4- 690 2,180 • 910 2,380 • 730 2,530 • 900 vascular resistance index (80- m m Hg - min �9 L -t �9 m 2)

Stroke volume 42.6 • 10.7 38.2 • 8.7 37.6 • 9.3 33.6 • 7.5 32.1 • 7.4 31.6 • 8.8 28.7 • 7.8 26.7 • 7.3 index (m 1 / m 2)

Right atrial 11 • 4 10 • 4 9 • 4 11 • 4 11 • 3 12 + 3 13 • 3 13 • 3 pressure ( m 1 / m 2)

~Values are means + SD. P < 0.002 for variation over time for all variables. bTimes: 1 = preinduction; 2 = postinduction; 3 = poststernotomy; 4 = five rain. post-CPB; 5 = ten min. post-CPB; 6 = twenty rain. post- CPB; 7 = thirty min. post-CPB; 8 = sixty min. post-CPB.

line slope differed from nil with P < 0.05. This method also compared direct and indirect methods within each patient over the entire study period. Measurement error was defined as ABP minus IBP, for which the mean and standard deviation were calculated for each measurement interval and for each patient. Thus, when IBP underestimated ABP, a positive measurement error was reported. Conversely, IBP overestimating ABP produced a negative measurement error. Backward stepwise regression was used to assess the significance of associations between measurement error and HR, SVRI, SVI, and CI. The positive or negative sign of the error remained intact for this analysis, and the algorithm included a patient identification code to correct for variability attributable to individual patients. Time of measurement was also included in the analysis.

RESULTS

The 8 measurement intervals generated 304 measurement sets, of which all but 2 were completed for the hemodynamic variables listed in Table 2. Analysis of variance showed statistically significant variation over

time in all variables listed (P < 0.002). HRs before cardiopulmonary bypass (CPB) reflect the influence of beta-adrenergic blockers, whereas those after CPB (times 4 to 7) were influenced by the common use of atrial or atrioventricular pacing at rates of 90 to 100 beats/min. CI peaked as ABP and SVRI reached their lowest values just after CPB, probably reflecting hemodilution. The decrease in SVI at time 4 followed from the increased HR, while the subsequent gradual decrease accompanies a decreasing CI and increasing SVRI.

Table 3 shows the Pearson product-moment correlations between DBP and IBP values over time. Of the 304 possible comparisons for each IBP method, missing values decreased this number by 14 measurements for oscillometric, 9 for auscultatory, 2 for return-to-flow, and 2 for the flicker methods, respectively. All IBPs correlated significantly with ABP (P < 0.001), with the highest correlations occurring most often at the first and last measurement times. For SBP, the 20- and 30- minute post-CPB IBPs usually correlated least with ABP. Flicker SBP correlation coefficients ranked last or next to last in 6 of the 8 periods. Oscillometric and

288 Journal of Clinical Monitoring Vol 6 No 4 October I990

Table 3. Pearson Product-Moment Correlations with Brachial Artery Pressure by Time

Indirect Blood Pressure 1 2 3 4

Time a

5 6 7 8

Systolic Oscillometry 0.87 0.63 0.81 Auscultation 0.91 0.81 0.75 Flicker 0.82 0.77 0.66 Return-to-flow 0.90 0.81 0.82

Mean Oscillornetry 0.69 0.59 0.78 Auscultation 0.85 0.73 0.73

Diastolic Oscillometry 0.82 0, 58 0.80 Auscultation 0.77 0.52 0, 56

0.70 0.80 0.71 0.64 0.87 0.81 0.81 0.65 0.68 0.81 0.75 0.76 0.68 0.47 0.84 0.75 0.82 0.71 0.63 0.80

0.69 0.77 0.71 0.63 0.79 0.73 0.60 0.71 0.67 0.84

0.84 0.58 0.51 0.65 0.75 0.49 0.57 0.71 0.68 0.82

*Times are defined in footnote to Table 2.

auscuhatory SBP correlations were similar. Correlation coefficients for MB P and DBP values were usually lower than those for their corresponding SBPs, although oscillometric DBP correlations at times 3 and 4 stand out as exceptions.

Figure 1 shows selected scatterplots for IBP versus ABP. For these comparisons, a measurement interval was selected that fell close to the median correlation coefficient and regression slope for each IBP method. Because mean and diastolic pressures produced similar regressions for oscillometric and auscuhatory IBPs, only oscillometric MBP and DBP scatter plots are

shown (Figs 1E and 1F). Figure 2 shows the scatterplots for each IBP method as compared with brachial ABP, combining all measurement intervals in all patients. Regression parameters for these plots are not reported because o f the variation over time demonstrated in Table 3.

Table 4 lists the correlations between ABP and IBP for each patient and method, showing various patterns to the scatter. Some individuals demonstrated a consistently wide scatter (low r) between DBP and IBP (patients 7 and 21), some showed consistently low scatter (patients 10, 19, and 35), and others showed a distinctly

0_ 03 16o O0

0 o - -

5.- 140

Q)

E 0 12o

J - -

0 09 ~o0

0

180" " / / *1 R - S q u a r e = 0 . 5 0 6 3 / N = 36

[] , / " /

j s ' t /

s . / 80

i i i I

80 I00 120 140 IBO 180

Brochiol SBP

180

13.. 123 180 OO

~ 1 4 0 0

0 4-- 120

0 (/~ 100

< 80

R - S q u a r e = 0 . 6 5 0 6 N = 37

,,~ ~ / [] /

//I~" Q /

rl ~ ~ D

I i I I i i I i i I

80 100 120 140 160 180

Brochiel SBP A B


:t60

O _ n n r~) :t4o

L

0 :t20 e ~

I,

:tOO

C

El / R - S q u a r e = 0 . 5 8 9 0 / "

N = 38 . ~ / "

o ~. , " 0 0 ~ / ~

0 / f / [] 121

0 ~ ' / C l O / /

o/ s-

�9 1 / / J / []

i i i i i i i

t00 :1.20 140 t60

Brochiol SBP

220

03 aoo b")

•0 :tBo

'160

I-0- :t40"

E :t20"

[ ~ '~00"

80'

R - S q u a r e = 0 6 4 3 6 / []

N = 37 / / I /

/ f / / sIS

/ / / /S

$S$ jS~

o~176 ~ ~.2 / ~

' i ' I ' i , i , I �9

80 :tOO 120 :t40 :t60 t80 200 220

D Brochiol SBP

O_ rn

0 Om

E

:t20

:tOO

0 80

0

0 60

E

o . / R - S q u a r e = 0 . 5 0 0 ~ o i /

N = 35 o /

0 0 / . / ' "

o/o ~_.,a" 5 "

0 zO

/zlzz ' ,/ 0 0 s /

//

i S f

i i I | i i I 60 80 :tO0 :t20

Brochiol MBP

:t20 O3 D

0 "L. t00

E 0 80

J o ~

O

O 60

o R - S q u a r e = 0 . 5 5 7 6 / ~ / /

I " l / j f / r

[] / t J S 0 0 0 0

f Z / / s ~ o S n

/ I I I I I I I

60 80 :tOO t20

Brochiol DBP

~I Fig 1. Scatterplots comparing indirect and intraarterial blood pressure values in mm Hg. Continuous lines show the best regression relationship. Equivalent values are shown by an interrupted line. (A) Automated oscillometric systolic blood pressure (SBP) at time 6 (r = 0.7I; y = 0.69x + 39; mean error = - 2 + I1). (B) Auscultatory S B P at time 5 (r = 0.81; y = 0.70x + 26; mean error = 8 + 12). (C) Flicker onset S B P at time 2 (r = O. 77; y = 0.84x + 27; mean error = - 8 +- I2). (D)Return-to-flow SBP at time 8 (r = 0.80; y = 0.79x + 19; mean error = 7 + 14. (E) Oscillometric mean blood pressure (MBP) at time 6 (r= 0.71; y = 0.85x + 19; mean error = - 6 + 10). (F) Oscil- lometric diastolic blood pressure (DBP) at time 8 (r = 0.75; y = 0.88x + 17; mean error = - 8 + I0).

290 Journal of Clinical Monitoring Vol 6 No 4 October 1990

220

[2_ 03 U'} le0.

0

.o iO0

03 0

A

60 "

60

~P

s ~ A P /

p / /

p , / 'A

~.'r A

i

I I t

I00 140 IBO 220

Brochiol Artery SBP

o_ 03

0 . m

5 03

0

B

i 6 0

120

/ P i

/ / s /

[] ~ o// n [] [] ~/J

[] O 0 13"

[] O 0 0 B n / " o,~ o-_r# o.~

0 [ ] [ ] 0 0

80' ~ o ~ooI:~ o

.r "~ 0 / /

40" I I

40 GO 120 IGO

Brochiol Artery MBP

o_ 03 C3

0 , m

k .

E o

, m

0 03

0

C

140'

120'

iO0"

80

60

r 40 ,

40

O0 O OO O ~/. 0 0 0 s O Q~O ,f,,

~ o

0

I i i

60 BO I00

/ J

J O J r

s f p

pP 0 p r

r

I

i20 i40

Brachial Artery DBP

220"

o_ rn (/) iao

o

0 140 - I - -

0 03 ~0o

<[

D

i 50 ,

60

/P

r p p

p r r

pP A p

p~

p l A

A A

A / , A A ' ~ . A & / /

/

' ; I I

lO0 140 180 220

Brachial Artery SBP

Fig 2. Scatterplots comparing indirect and brachial intraarterial blood pressure values in mm Hg, combining all measurements in all patients, shown with a line of equivalent values. (A) Auto- mated oscillometric systolic blood pressure (SBP). (B) Automated oscillometric mean blood pressure (MBP). (C) Automated oscillometric diastolic blood pressure (DBP). (D) Auscultatory SBP. (E) Auscultatory MBP. (F) Auscultatory DBP. (G) Flicker onset SBP. (H) Return-to-flow SBP.


160"

0..

L~ 12o

2 '

~ 8o

4 0 -r

4O

/ / / P

/ / / n

/ /

o Oz /

m ~o

p

f / / /

80 120 161

Brochiol Artery MBP

~20 '

n m C3 Ioo ,

k=.

0 8O

.f.==

0 {,0 6O ='I

.<

40 "

40

O

o / / . p

/ . /

0 0 0 / / /

O / i /

0 OO O 0 ~/

O O / " o %g r L ~

r O O. / Or162 O O O

O O ~ O r , 0 0 ~ < r ~ 0 0 , 0 0 01, /

~0 "0 00000, O~ 0 O OO OO P 0~0 ,00 /

O r 1 6 2 OO O o 0 0 ~ r / 0 o 0 0

O OOr ~," O OO O 00,

OO O O O

o~ ,~'o p

0 O 0 ~ f

I I I

50 80 100

Brochial Artery DBP

i20

230"

0... i 9 o

m U3

~ t 5 0

0 e ~

L L t l O

G

70 "

70

/ / J / /

/ A i /

, r

J "

A "*. . A / /

p / A

I t I

110 150 t 9 0 230

Brachial Artery SBP

230"

[3_ 133 (/3

l g 0

0 I ,

O t5o.

C

n,"

r p

4 p / /

,," & / /

A / " / , * ,

/ J " /

/

A A

I I

~0 150

70

70 ~90 230

H

Brachial Artery SBP

Fig 2. (Continued)

greater (oscillometric SBP and MBP in patient 28, auscultatory DBP in patients 8 and 37) or lesser (oscillometric MBP and DBP in patient 13, return-to-flow SBP in patient 28) scatter with one particular IBP method. Review of these patients' demographic and hemodynamic parameters fails to provide obvious expla- nations for these patterns.

Table 5 characterizes the measurement errors and

regressions averaged over all patients and intervals. On average, auscuhatory and return-to-flow methods underestimated intraarterial SBP, while flicker overestimated and oscillometry closely approximated arterial SBP. Both oscillometry and auscultation overestimated MBP and DBP. The ranges and standard deviations of the errors show that individual patients and individual measurements varied widely from the population's


Table 4. Pearson Product-Moment Correlations with Brachial Artery Pressure for Each b~direct Blood Pressure Technique for Individual Patients

Systolic Mean Diastolic

Patient No. Oscillometry Auscultation Flicker Return-to-Flow Oscillometry Auscultation Oscillometry Auscultation

1 0.77 0.70 0.73 0.75 0.88 0.90 0.85 0.92 2 0.78 0.95 0.96 0.94 0.79 0.90 0.94 0.80 3 0.51 0.40 0.77 0.62 0.44 0.89 0.44 0.95 4 0.69 0.87 0.81 0.37 0.41 0.78 0.80 0.56 5 0.81 0.71 0.74 0.33 0.51 0.10 0.53 0.75 6 0.72 0.35 0.41 0.50 0.73 0.52 0.50 0.69 7 0.18 0.43 0.10 0.20 0.53 0.28 0.62 0.57 8 0.90 0.89 0.79 0.91 0.90 0.74 0.90 0.25 9 0.79 0.91 0.89 0.93 0.12 0.86 0.17 0.64

10 0.95 0.90 0.97 0.97 0.89 0.96 0.89 0.91 11 0.99 0.98 0.96 0.99 0.95 0.95 0.94 0.85 12 0.90 0.93 0.89 0.96 0.91 0.97 0.98 0.97 13 0.06 0.51 0.11 0.13 0.95 0.17 0.88 0.49 14 0.29 0.46 0.49 0.48 0.63 0.83 0.77 0.83 15 0.79 0.58 0.86 0.87 0.67 0.62 0.79 0.47 16 0.62 0.77 0,83 0.69 0.60 0.81 0.69 0.72 17 0.20 0.58 0.89 0.44 0.65 0.57 0.92 0.46 18 0.74 0.88 0.73 0.91 0.92 0.89 0.84 0.80 19 0.82 0.91 0.81 0.88 0.92 0.97 0.95 0.93 20 0.90 0.91 0.69 0.95 0.96 0.91 0.93 0.92 21 0.70 0.38 0.62 0.51 0.45 0.34 0.08 0.20 22 0.67 0.71 0.84 0.57 0.77 0.83 0.52 0.70 23 0.91 0.95 0.76 0.97 0.50 0.68 0.79 0.57 24 0.97 0.82 0.89 0.99 0.96 0.81 0.57 0.84 25 0.34 0.89 0.91 0.90 0.37 0.87 0.74 0.86 26 0.82 0.99 0.85 0.95 0.88 0.94 0.91 0.97 27 0.67 0.91 0.72 0.86 0.04 0.87 0.59 0.74 28 0.05 0.68 0.69 0.95 0.27 0.47 0.54 0.68 29 0.78 0.67 0.73 0.45 0.61 0.73 0.39 0.61 30 0.46 0.31 0.36 0.53 0.73 0.10 0.80 0.20 31 0.69 0.88 0.87 0.76 0.67 0.75 0.80 0.79 32 0.92 0.98 0.92 0.90 0.95 0.75 0.94 0.35 33 0.64 0.90 0.57 0.80 0.47 0.75 0.33 0.52 34 0.94 0.93 0.79 0.90 0.99 0.97 0.97 0.93 35 0.91 0.96 0.95 0.87 0.96 0.93 0.86 0.81 36 0.73 0.94 0.89 0.86 0.77 0.94 0.81 0.85 37 0.80 0.85 0.85 0.88 0.87 0.52 0.85 0.18 38 0.85 0.71 0.06 0.71 0.86 0.97 0.95 0.84

m e a n m e a s u r e m e n t e r r o r . In s o m e p a t i e n t s , m e a s u r e -

m e n t e r r o r fel l m a i n l y o n o n e s ide o f t h e m e a n t h r o u g h -

o u t t h e p r o c e d u r e , w h i l e in o t h e r s th i s v a r i e d w i d e l y o r

c h a n g e d d i r e c t i o n o v e r t h e c o u r s e o f t h e p r o c e d u r e (Figs

3 to 5). T h e i n t e r c o n n e c t i o n o f p o i n t s d o e s n o t i m p l y

c o n t i n u i t y , b u t s e r v e s r a t h e r to ass i s t t h e eye i n f o l l o w -

i n g a p a r t i c u l a r I B P m e t h o d o v e r t h e m e a s u r e m e n t i n -

t e r v a l s s e l ec t ed .

T a b l e 6 s u m m a r i z e s t h e s t e p w i s e r e g r e s s i o n ana ly se s .

Fig 3, Systolic pressure differences (in mm Hg) at different times during surgery. Times are described in Materials and Methods; M represents the mean of the 8 measurement times. Solid squares show the mean difference for all 38 patients. Other connected symbols display pressure differences (measurement error) over time in individual patients selected to represent the variety of patterns observed. (A) Intraarterial systolic blood pressure (SBP) minus oscillometric SBP. (B) Intraarterial SBP minus auscultatory SBP. (C) lntraarterial SBP minus flicker SBP. (D) Intraarterial SBP minus return-to-flow SBP.

Table 5. Measurement Errors and Regression Parameters a by Indirect Blood Pressure Method

Sys to l i c M e a n Dias to l i c

O s c i l l o m e t r y A u s c u l t a t i o n Fl icker R e t u r n - t o - F l o w O s c i l l o m e t r y A u s c u l t a t i o n O s c i l l o m e t r y A u s c u l t a t i o n

E r r o r M e a n 0 9 - 5 7 - 6 - 3 - 9 - 8

S D 11 9 11 9 8 6 7 7 L o w - 12 - 10 - 2 7 - 13 - 14 - 17 - 19 - 2 1 H i g h 18 30 10 29 6 10 6 3

I n d i v i d u a l L o w - 45 - 23 - 43 - 35 - 36 - 30 - 39 - 49 H i g h 43 45 43 52 32 2 8 23 27

M e a n c o r r e l a t i o n coef f ic ien t 0 .69 0 .77 0 .73 0 .74 0 .70 0 .73 0 .73 0 .69

S D 0 .25 0 .20 0 .24 0 .24 0 .25 0 .25 0 .23 0 .23

M e a n s lope 0 .84 0 .86 0 .88 0 .88 0 .70 0 .85 0.6-3 0 .68

S D 0 .43 0.51 0.51 0 .53 0 .36 0 .38 0 .34 0 .43

M e a n y i n t e r cep t 18 23 9 20 21 10 19 15

S D 52 58 65 61 32 33 2 4 32

C r o s s o v e r 113 164 75 167 70 67 51 47

~Error: For brachial arterial blood pressure minus indirect blood pressure, SD of mean error represents the mean SD of the 38 individual mean errors. Low and high mean errors represent the lowest and highest mean measurement errors, respectively, among the 38 patients. Low and high individual errors represent the lowest and highest errors recorded in individual measurements from any patient, Mean correlation coefficient and mean slope are the mean regression parameters derived by averaging those from each patient, Mean y intercept is the mean brachial artery pressure at which the extrapolated indirect blood pressure reaches zero, obtained by averaging the intercepts o f all patients. Crossover represents the pressure (mm Hg) at which the average regression line crosses the line o f perfect agreement between indirect and direct blood pressure,

Oscil lometric Systolic 60.

i5 w

~ A

-2o l a. -40

-60 . . . . . . . . .

6O

8 40

~ 20 Q

-, 0

if- -2o

A

-40

Auscultatory Systolic

X

A

i I I 1 i i I i I

0 1 2 3 4 5 6 7 8 M 0 1 2 3 4 5 6 7 8 M Time Time

B

8 C:

13.

C

Flicker Systolic Return to Flow Systolic 40 60

Ool : ,o ; ~ 20

/5 .~ 0

-20 "i x ~ -20 n

, -40 - 4 0 . . . . . . . . . . . . . . . . . 0 1 2 3 4 5 6 7 8 M 0 1 2 3 4 5 6 7 8 M

Time Time D

294 Journal of Clinical Monitoring Vol 6 No 4 October I990

40-

~) 20, i - -

I:::1 O.

ffl

-20. L .

-40

A

Oscil lometric Mean BP

l @

&

x

1 i I I I l l I

2 3 4 5 6 7 8 M Time

Ausculatory Mean

20 ,~ + e - o

i5 ~ _10 1

:~ -20 o

-30

0 1 2 3 4 5 6 7 8 M

Row Numbers B

Fig 4. Mean arterial blood pressure (MBP) differences (mm Hg) at different times during surgery. Times and symbols are described in Figure 3. (A) Intraarterial MBP minus oscillometric MBP. (B) Intraarterial MBP minus auscuhatory MBP.

Osci l lometr ic Diastolic Auscul tatory Diastol ic 4o 3o

~176 l . 8 2 8 ~- ,- 10

2 o #= o .

�9 .~ -10 �9

m -20 ~. -20-~ + ~ []

f o.. -30

-4O . . . . . . . . , -40

0 1 2 3 4 5 6 7 8 M 0 1 2 3 4 5 6 7 8 M Time Time

A B

Final R 2 represents the fraction of IBP measurement error cumulatively attributable to variation in the hemodynamic parameters listed. To determine the influence on measurement error predicted by the model, an incremental change in the unit value of the hemodynamic predictor (e.g., SVRI, SVI, HR) is multiplied by the beta value to yield the predicted change (mm Hg) in IBP measurement error. The P value reports the statistical significance of this association. Except for osciUometric

Fig 5. Diastolic blood pressure (DBP) differences (mm Hg) at different times during surgery. Times and symbols are described in Figure 3. (A) Intraarterial DBP minus oscillometric DBP. (B) Intraarterial DBP minus auscultatory DBP.

diastolic blood pressure, various combinations of HR, SVI, SVRI, and CI were associated with measurement error. The cumulative effects explained more than half of the observed variation (R 2 > 0.50) only for return-to- flow SBP, flicker SBP, and auscultatory SBP and MBP.


Table 6. Stepwise Regression for Hemodynamic Variables Contributing Significantly to Indirect Blood Pressure Measurement Error

Variable (Final R 2) Beta P Value

Systolic Auscultation (0.52)

Systemic vascular resistance index 0 .0056 0.000I Stroke volume index 0.33 0.0044 Heart rate 0.14 0.0098

Flicker (0.51) Heart rate 0.30 0.0001 Systemic vascular resistance index 0 .0079 0.0001 Stroke volume index 0.49 0.0003

Return-to-flow (0.51) Systemic vascular resistance index 0 .0050 0.0003 Cardiac index 3.49 0.018

Oscillometry (0.37) a Cardiac index 7.19 0.0001 Systemic vascular resistance index 0 .0062 0.0004

Mean Auscultation (0.59)

Heart rate 0.22 0.0001 Stroke volume index 0.48 0.0001 Systemic vascular resistance index 0.0064 0.0001

Oscillometric (0.34) Systemic vascular resistance index 0 .0064 0.0001 Cardiac index 5.61 0.0001 Heart rate - 0.077 0.025

Diastolic b Auscultation (0.48)

Heart rate 0.19 0.0001 Systemic vascular resistance index 0 .0039 0.0002 Stroke volume index 0.30 0.0015

~Measurement time also influenced measurement error for oscillometric systolic blood pressure (P < 0.05). bNo hemodynamic parameters correlated with oscillometric diastolic measurement error.

For oscillometric SBP, measurement period also influenced the size o f the error, as suggested by observing the mean pressure difference in Figure 3A.

DISCUSSION

Our principal findings are that the relationship between noninvasive and directly measured arterial blood pressure varies substantially between patients, over time, and with systemic hemodynamic conditions. In some patients the IBP and ABP correlate so weakly as to ren- der one or more IBP methods diagnostically ineffective. Aside from unexplained wide variation in IBP, clinical clues suggesting this occurrence appear elusive.

In previous studies, relationships between IBP and ABP have varied widely in linear correlation [1,3,5,6,8- 10,12,18-31]. The distinction between measurement error and linear correlation warrants emphasis. The

mathematical difference between ABP and IBP defines measurement error, assuming that ABP measured with a properly calibrated high-fidelity monitoring system represents the desired standard. The linear correlation coefficient assesses how closely the data points fit a straight line [32]. A high correlation coefficient may occur despite important differences between two measurements [33]. When two measurements are expected to be nearly identical, the slope and y intercept assume considerable importance. If the difference between ABP and IBP is predominantly positive, then most of the regression line lies to the right of the line of equiva- lence (see Fig 1B). The direction or magnitude of the IBP-ABP difference might also change importantly within the usual clinical blood pressure range. The regression line in Figure 1A exhibits this tendency. Here the correlation efficient (r = 0.71) is only moderate when compared with the desired level (r > 0.90) for an IBP-ABP comparison. The correlation coefficient tends to increase i f the range of values increases; thus, fairly tight control of blood pressure might bias our data toward lower r values.

Authors comparing IBP and ABP vary in their emphasis o f linear correlation versus measurement error. Either method appears appropriate for comparing two measurements when one of them serves as an accurate standard against which to calibrate the other [33]. Pool- ing multiple blood pressure measurements from different patients highlights data scatter, but it may overlook striking IBP inadequacies in some individuals (see Table 4 and Figs 3 to 5). Some studies suggest a consistent direction of measurement error within single patients, supporting accurate diagnosis of blood pressure changes despite consistent overestimation or underestimation of arterial blood pressure [6,22-34,35]. Figures 3 to 5 illus- trate the inadequacy of this assumption for some patients, whose measurement errors shifted unpredictably in direction and magnitude. Standard deviations for the mean correlation coefficients, slopes, and intercepts (Table 5) further reflect striking interpatient variability in the IBP-ABP relationship when these comparisons are based on single measurements.

A number o f studies have shown IBP-ABP correlation coefficients exceeding 0.90, particularly for SBP [1,9,20,21,23-26,28,34,36,37], which are considerably higher than those reported in this article. This probably reflects differences in measurement techniques or in the hemodynamic stability of the patients studied. Some authors have used two to ten successive IBP measurements for an individual comparison with ABP [9,23,27- 29,34,36-39]. Predictably, these studies usually produce higher correlation coefficients than those using (or apparently using) single IBP measurements [5,6,10,12,


22,24,25]. Averaging repeated measurements reduces the scatter of any measurement comparison, especially with imprecise ones. Interobserver variation might also reduce linear correlations, although this was eliminated in the present study by using a single observer.

The definition of ABP varies from study to study, and the Association for the Advancement of Medical Instrumentation (AAMI) standard offers two options [5]. The first option defines ABP as an envelope including the range of ABPs taken from individual pulses measured over an IBP cuff inflation period. Choosing this option reduces measurement error when compared with measuring and averaging beat-to-beat intraarterial SBP, DBP, and MBP over the same period [5], which represents the second option. The present method approximates the latter by selecting midexhalation pulse waves for SBP and DBP measurement. This method would be undesirable when the arterial blood pressure is rapidly changing or varies substantially over the respiratory cycle. As previously noted, measurements were repeated when MBP variation exceeded 5 mm Hg during each complete set of hemodynamic measurements. Respiratory variation in arterial SBP sel- dom exceeded 5 mm Hg (less for MBP and DBP), per- haps because intravascular volume was closely monitored and aggressively treated. Some studies have biased the direction of measurement error by selecting either end-expiratory or highest SBP for comparison [12, 30,40]. Simultaneous IBP and ABP values have been obtained in some studies by using opposite arms. The advantages and disadvantages of "same time" versus "same place" comparisons have been studied by Finnie et al [4] and discussed by Whalen and Ream [5]. The use of bilateral simultaneous cuff inflation precluded simultaneous IBP-ABP comparisons in the present study. Methodologic differences in ABP definition would affect SBP and DBP more than MBP. Regardless of the method used to identify arterial blood pressure, the range of measurement errors reported with single IBP measurements is large, usually being comparable to those in Table 5 [2,6,10,12,23,27,31,34,38,40-42].

The selection of cardiac surgical patients for intra- operative blood pressure measurements probably biases the IBP versus ABP comparisons toward less perfect agreement. Previous investigations have used such patients for some or all of their IBP/ABP comparisons [4-6,8,24]. Green et al [6] described apparently arbitrary measurement error variation, and Whalen and Ream [5] showed larger errors in the period surrounding CPB. The present correlation coefficients for SBPs tended to be highest before anesthetic induction and 60 minutes after CPB, confirming the observations of Whalen and Ream. Those authors postulated that rapid ABP fluctu-

ations during the Dinamap inflation-deflation cycle might cause this. This mechanism for reduced peri-CPB IBP accuracy may be correct, but variations in SVRI, HR, SVI, and CI over time appear to also play a role (see Tables 2 and 6). Oscillometric SBP was the only IBP for which the time of measurement significantly influenced measurement error, resulting from its iso- lated overestimation of ABP just after separating from CPB (time 4). Because brachial and radial arterial pressures often underestimate central aortic SBP and MBP at that time [17,43], oscillometry might offer a valuable "second opinion" when this phenomenon is suspected.

Other studies have found that the direction of IBP error varies with the level of ABP, in particular showing a tendency for automated oscillometry to overestimate at low SBPs and to underestimate at high SBPs [9,11,22,30,41]. The present study suggests the same tendency (see Figs 1A and 2A). Studies conducted during induced hypotension verify the propensity of automated oscillometry to overestimate at low ABPs [9,22]. More recent Dinamap automated oscillotonometry models have altered the measurement algorithm, which might significantly improve correlations and reduce measurement error.

Clinical interpretation of the hemodynamic correlations generated by stepwise regression proves complex. In general, increases in HR and SVRI increase the measurement error, but the presence of positive and negative measurement errors complicates this interpretation. By using auscultatory SBP as an example, the algorithm predicts that a 37 bpm increase in HR would (on average) increase the measurement error by 5 mm Hg. For flicker SBP, a 13 bpm rise would produce the same change. Assuming the same (5 mm Hg) increase in auscultatory SBP measurement error, the necessary incre- ments in SVI and SVRI would be 15 and 893 units, respectively. The higher the beta value, the smaller is the incremental change needed to produce a given increase in measurement error. However, these regressions span a range of negative (arterial BP < IBP) and positive (arterial BP > IBP) differences, so this "increased" difference would decrease the measurement error when IBP substantially exceeds arterial BP. This situation would most often arise with indirect DBPs. Because the measurement errors range from - 4 9 to + 52 mm Hg, the algorithm suggests that a particular numeric range for each hemodynamic correlate might minimize IBP measurement error, potentially produc- hag optimal "windows" o fHR, CI, SVI, or SVRI combinations.

Previous studies have found little or no correlation between systemic hemodynamics and ABP versus IBP measurement error [1,3]. Cohn [2] showed that sys-


temic and regional vasoconstriction caused auscultatory blood pressures to markedly underestimate brachial or femoral intra-arterial BP. Finnie et al [4] also found large auscultatory blood pressure measurement errors in 3 patients with markedly elevated systemic vascular re- sistances. Hut ton and Prys-Roberts [44] suggested HR as a theoretical determinant of oscillometric MBP measurement error. HR significantly influenced oscillometric MBP error in the present study, but the effect was small (beta 0.077) and the correlation was direction- ally opposite to what Hutton and Prys-Roberts predicted. Green et al [6] found no correlation between HR and oscillometric blood pressure error. Chyun [3] found a high correlation between HR and auscultatory DBP measurement error (r = 0.89, P < 0.001), which resem- bles the present findings. Borow and Newburger [1] evaluated ascending aortic pressures, Dinamap cuff pressures, and systemic hemodynamics in 30 patients undergoing cardiac catheterization, finding no significant correlation between measurement error and HR, CO, and SVR. Their IBP-ABP comparisons were performed under less variable hemodynamic conditions, as reflected by a narrower range of HRs (49 to 94 versus 46 to 140 bpm), COs (1.6 to 4.6 versus 2.7 to 9.9 L/min), and SVRIs (590 to 2,200 versus 445 to 2,750 in identical units). Also, those authors took a single set of measurements on patients undergoing cardiac catheterization, whereas the present observations followed changing hemodynamics through cardiac surgery. These differences may account for the apparent dis- agreement.

In conclusion, single measurements of IBP by 4 different methods correlate moderately well with ABP, but are disappointing in comparison with ideal clinical performance. With present techniques, only auscultatory MBP fell within the accuracy guidehnes proposed by AAMI (intrapatient mean error < 5 m m Hg, SD < 8 mm Hg) [24]. Measurement error varies widely both within and between patients. Interobserver error was not assessed in this study, but it might further increase measurement error for the auscultatory, return-to-flow, and flicker onset methods. Clinically useful predictors of measurement error magnitude and direction are not readily apparent, but systemic hemodynamics significantly influence the error. Measurement errors some- times change erratically, such that consecutive IBP measurements may falsely suggest a substantial blood pressure alteration or fail to identify a truly significant one. In some patients, one or more IBP methods may perform unacceptably. None of the 4 IBP methods tested offers dearly superior clinical performance, and the correlations and error ranges for SBPs, MBPs, and DBPs were proportionately similar. Averaging fie-

quently repeated IBP measurements should attenuate these problems, although frequent cycling of automatic cuff devices may risk complications from ischemia or venostasis [45,46]. It follows that continuous IBP methods should theoretically improve diagnostic accuracy. While immediate repetition of questionable blood pressures is advised, consideration should also be given to changing to a different IBP method when blood pressure measurements vary excessively or appear inconsistent with other clinical signs. Direct measurement of arterial BP appears advisable when difficulties persist or when hemodynamic instability appears likely.

Presented in part at the annual meeting of the American Soci- ety of Anesthesiologists, New Orleans, LA, Oct 1984.

The authors gratefully acknowledge the assistance and sugges- tions of L. Douglas Case, PhD, and Brian Horan, MB, BS.

REFERENCES

1. Borow KM, Newburger JW. Noninvasive estimation of central aortic pressure using the osciUometric method for analyzing systemic artery pulsatile blood flow: comparative study of indirect systolic, diastolic, and mean brachial artery pressure with simultaneous direct ascending aortic pressure measurements. Am Heart J 1982;103:879-886

2. CohnJN. Blood pressure measurement in shock. Mecha- nism of inaccuracy in auscultatory and palpatory methods. JAMA 1967;199:118-122

3. Chyun DA. A comparison of intra-arterial and auscultatory blood pressure readings. Heart Lung 1985;14:223- 228

4. Finnie KJC, Watts DG, Armstrong PW. Biases in the measurement of arterial pressure. Crit Care Med 1984; 12:965-968

5. Whalen P, Ream AK. A quantitative evaluation of the Hewlett-Packard 78354A noninvasive blood pressure me- ter. J Clin Monit 1988;4:21-30

6. Green M, Paulus DA, Roan VP, van der Aa J. Compari- son between oscillometric and invasive blood pressure monitoring during cardiac surgery. Int J Clin Monit Comput 1984;1:21-26

7. Snyder NC, Lichtor JL, Schreider B. Evaluation of an automatic blood pressure monitor in children. Anesthe- siology 1984;61:A174

8. van Egmond J, Hasenbos M, Crul JF. Invasive v. noninvasive measurement of arterial pressure: comparison of two automatic methods and simultaneously measured direct intra-arterial pressure. Br J Anaesth 1985;57:434-A.A.A

9. Gourdeau M, Martin R, Lamarche Y, Tetreault L. Oscil- lometry and direct blood pressure: a comparative clinical study during deliberate hypotension. Can Anaesth Soc J 1986;33:300-307

10. Yelderman M, Ream AK. Indirect measurement of mean blood pressure in the anesthetized patient. Anesthesiology 1979;50:253-256


11. Hutton P, Dye J, Prys-Roberts C. An assessment of the Dinamap 845. Anaesthesia 1984;39:261-267

12. Bruner JMR, Krenis LJ, Kunsman JM, Sherman AP. Comparison of direct and indirect methods of measuring arterial blood pressure. Med Instrum 1981;15:11-21, 97- 101, 182-188

13. Kirkendall WM, Feinleib M, Freis ED, Mark AL. Recom- mendations for human blood pressure determination by sphygmomanometers: subcommittee of the AHA Post- graduate Education Committee. Stroke 1981;4:555A- 564A

14. Gardner RM. Direct blood pressure measurement-- dyffamic response requirements. Anesthesiology 1981;54: 227-236

15. Wood EH. Physical response requirements of pressure transducers for the reproduction of physiological phe- nomena. Trans Am Institute Electrical Engineers [part I] 1956;75:32-40

16. Rothe CF, Kim KC. Measuring systolic arterial blood pressure: possible errors from extension tubes or dispos- able transducer domes. Crit Care Med 1980;8:683-689

17. Gravlee GP, Wong AB, Adkins TG, et al. A comparison of radial, brachial, and aortic pressures after cardiopulmonary bypass. J Cardiothorac Anesth 1989;3:20-26

18. Runciman WB, Rutten AJ, llsley AH. An evaluation of blood pressure measurement. Anaesth Intesive Care 1981; 9:314-325

19. O'Callaghan WG, Fitzgerald DJ, O'Malley K, O'Brien E. Accuracy of indirect blood pressure measurement in the elderly. Br Med J 1983;286:1545-1546

20. Park MK, Robotham JL, German VF. Systolic pressure amplification in pedal arteries in children. Crit Care Med 1983;11:286-289

21. Park MK, Menard SM. Accuracy of blood pressure measurement by the Dinamap monitor in infants and children. Pediatrics 1987;79:907-914

22. Gloyna DF, Huber P, Abston P, Arens JF. A comparison of blood pressure measurement techniques in the hy- potensive patient (abstr). Anesth Analg 1984;63:222

23. Breit SN, O'Rourke MF. Comparison of direct and indirect arterial pressure measurements in hospitalized patients. Aust N Z J Med 1974;4:485-491

24. Davis RF. Clinical comparison of automated auscultatory and oscillometric and catheter-transducer measurements of arterial pressure. J Clin Monit 1985;1:114-119

25. Pereira E, Prys-Roberts C, DagninoJ, et al. Auscultatory measurement of arterial pressure during anaesthesia: a reassessment of Korotkoff sounds. Eur J Anaesthesiol 1985;2:11-20

26. Ramsey M. Noninvasive automatic determination of mean arterial pressure. Med Biol Eng Comput 1979;17: 11-18

27. Venus B, Mathru M, Smith RA, Pham CG. Direct versus indirect blood pressure measurements in critically ill patients. Heart Lung 1985;14:228-231

28. Colan SD, Fujii A, Borow KM, et al. Noninvasive determination of systolic, diastolic, and end-systolic blood pressure in neonates, infants and young children: comparison with central aortic pressure measurements. Am J Cardiol 1983;52:867-870

29. Friesen RH, Lichtor JL. Indirect measurement of blood pressure in neonates and infants utilizing an automatic noninvasive oscillometric monitor. Anesth Analg 1981; 60:742-745

30. Loubser PG. Comparison of intra-arterial and automated oscillometric blood pressure measurement methods in postoperative hypertensive patients. Med Instrum 1986; 20:255-259

31. Nystrom E, Reid KH, Bennett R, et al. A comparison of two automated indirect arterial blood pressure meters: with recordings from a radial arterial catheter in anesthetized surgical patients. Anesthesiology 1985;62:526- 530

32. Glantz SA. Primer of biostatistics. New York: McGraw Hill, 1981:210-217

33. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307-310

34. Vardan S, Mookherjee S, Warner R, Smulyan H. Systolic hypertension. Direct and indirect BP measurements. Arch Intern Med 1983;143:935-938

35. Hausman D, Rommelsheim K. Automatic non-invasive blood pressure determination-comparative determinations and experiences with the DINAMAP Vital Data 845 XT monitor in the intensive care station. Anasth Intensiv- ther Notfallmed 1983;18:93-97

36. Holland WW, Humerfelt S. Measurement of blood- pressure: comparison of intra-arterial and cuff values. Br Med J 1964;2:1241-1243

37. Hunyor SN, FlynnJM, Cochineas C. Comparison of performance of various sphygmomanometers with intraarterial blood-pressure readings. Br Med J 1978;2:159-162

38. Raftery EB, Ward AP. The indirect method of recording blood pressure. Cardiovasc Res 1968;2:210-218

39. Kimble KJ, Darnall RA, Yelderman M, et al. An automated oscillometric technique for estimating mean arterial pressure in critically ill newborns. Anesthesiology 1981; 54:423-425

40. Berliner K, Fujiy H, Lee DH, et al. The accuracy of blood pressure determinations: a comparison of direct and indirect measurements. Cardiologia 1960;37:118-128

41. Rutten AJ, llsley AH, Skowronski GA, Runciman WB. A comparative study of the measurement of mean arterial blood pressure using automatic oscillometers, arterial can- nulation and auscultation. Anaesth Intensive Care 1986; 14:58-65

42. Van Bergen FH, Weatherhead DS, Treloar AE, et al. Comparison of indirect and direct methods of measuring arterial blood pressure. Circulation 1954;10:481-490

43. Stern DH, Gerson JI, Allen FB, Parker FB. Can we trust the direct radial artery pressure immediately following cardiopulmonary bypass? Anesthesiology 1985;62:557- 561

44. Hutton P, Prys-Roberts C. The oscillotonometer in the- ory and practice. Br J Anaesth 1982;54:581-591

45. Sy WP. Ulnar nerve palsy possibly related to use of auto- matically cycled blood pressure cuff. Anesth Analg 1981; 60:687-688

46. Showman A, Betts EK. Hazard of automatic noninvasive blood pressure monitoring (letter). Anesthesiology 1981; 55:717-718

Documents

Accuracy of four indirect methods of blood pressure measurement… · 2017. 8. 26. · IBP and intraarterial blood pressure (ABP) [1-4], and few studies have closely evaluated inter-patient