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© 2001 International Anesthesia Research Society
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Abstract |
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Twenty patients scheduled for coronary artery bypass grafting had their ear and finger oximeter and radial artery blood pressure (Bpmeas) waveforms collected. The ear and finger pulse oximeter waveforms were analyzed to extract beat-to-beat amplitude and area and width measurements. The Bpmeas waveforms were analyzed to measured systolic blood pressure (BP), mean BP, and pulse pressure. The correlation coefficient was determined between the derived waveforms from the pulse oximeter and Bpmeas for the first 10 patients. The ear pulse oximeter width (WidthEar) had the best correlation (r = 0.8). Linear regression was done between WidthEar and Bpmeas based on slope (b) and intercept (a) values, BP was calculated (Bpcalc) in the next 10 patients as:
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where i = systolic BP, mean BP, and pulse pressure. The initial bias was too large to be clinically useful. To improve clinical applicability a period of calibration was introduced in which the first 50 readings of WidthEar and Bpmeas for each patient were used to calculate the intercept. After calibration the systolic BP, mean BP and pulse pressure bias values were -2.6, -1.88 and -1.28 mm Hg, and the precision values were 15.9 10.09, and 9.94 mm Hg, respectively. The present attempt to develop a clinically useful method of noninvasive BP measuring was partly successful with the requirement of a calibration period.
IMPLICATIONS: Statistical comparison was made between measured blood pressure (BP) from arterial line and calculated BP derived from ear pulse oximeter waveform in 10 patients undergoing coronary artery bypass graft surgery. Using 62,077 paired readings, the mean difference for systolic BP, mean BP, and pulse pressure between the 2 methods was -2.6, -1.88, and -1.28 mm Hg, respectively.
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Introduction |
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Over the last decade, the pulse oximeter has become a standard clinical monitor in both the operating room and intensive care environment. This noninvasive monitor normally provides information about arterial oxygen saturation and heart rate (1). Pulse oximetry works by using light at 2 wavelengths (660–940 nm). The light is transmitted through tissues, sensed by a photodetector, amplified, and processed (2). The arterial oxygen saturation and heart rate are displayed on a screen. With additional analysis, it may be possible for the same device to measure other important clinical variables. A high correlation has been found between plethysmographic waveforms and blood pressure oscillations in normal subjects by using spectral-domain analysis. Furthermore, both measurements respond similarly to cardiovascular challenge, i.e., sympathetic activation induced by active standing (3). Despite the availability of the pulse oximeter waveform on most modern monitors, the underlying physiology is not well understood. The lack of understanding requires an empiric approach to its analysis. This article outlines an attempt to measure blood pressure (BP) noninvasively on a beat-to-beat basis by using the pulse oximeter waveform.
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Methods |
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Data Collection
With IRB approval, 20 patients (14 males and 6 females) scheduled for elective coronary artery bypass graft surgery (CABG) at Yale-New Haven Hospital had their ear and finger oximeter and radial artery BP waveform signals collected. Patients with an intracardiac shunt, aortic or mitral valve disease, or poor ejection fraction (<30%) were excluded. Anesthesia consisted of a narcotic-based technique with inhaled anesthesia (isoflurane) as dictated by clinical practice. A Bair Huggerwarming unit (Model 505; Augustine Medical, Inc., Eden Prairie, MN) was applied at the start of the procedure.
Plethysmographic monitoring was obtained with fixed-gain pulse oximeters using conventional ear and finger probes (Oxypleth; Novametrix Medical Systems Inc., Wallingford, CT). The ipsilateral radial artery was cannulated (Arrow 20-gauge; Arrow International Inc., Reading, PA) and connected via pressure tubing (48 in. [120 cm], Model 50-P248; Baxter Healthcare Corporation, Irvine, CA) to a transducer (Transpac IV Monitoring Kit; Abbott Critical Care Systems, Abbott Laboratories, North Chicago, IL) interfaced with a monitor (SpaceLabs Model #90305; SpaceLabs, Inc. Redmond WA). Both plethysmographic and the radial artery BP tracings (BPmeas) were recorded at 250 Hz with a microprocessor-based data acquisition system using commercially available data acquisition software (SnapMaster; HEM Data Corp., Southfield, MI). The ear and finger pulse oximeter waveforms were then analyzed to extract the beat-to-beat amplitude, area, and width measurements using the Igor wave analysis program(Wave Metric Inc., Lake Oswego, OR). The width is determined at the half height of the amplitude of each pulse oximeter beat. It is measured in seconds.
The plethysmographic waveform variables hereafter will be labeled as follows: ear pulse oximeter amplitude (AmpEar), finger pulse oximeter amplitude (AmpFinger), ear pulse oximeter area (AreaEar), finger pulse oximeter area (AreaFinger), ear pulse oximeter width (WidthEar) and finger pulse oximeter width (WidthFinger). The interpretation of the data was done in three phases.
Phase 1
In the first 10 patients, pulse oximeter waveforms (width, area, and amplitude) of the ear and finger were compared with the measured radial artery BP derived waveforms (systolic BPmeas, mean BPmeas, and pulse pressuremeas) to identify the plethysmographic waveform that had the best correlation coefficient. R values above 0.6 were considered to be significant. Using simple linear regression equation of the form y = a + (b x x) where y = (BPmeas), a = intercept, b = slope, and x = best correlated parameter.
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where i = systolic BP, mean BP, and pulse pressure.
Phase 2
In the next phase, we used the derived equation (Equation 2) to see if the best correlated parameter could be used to calculate BP (BPcalc).
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where i = systolic BP, mean BP, and pulse pressure.
The agreement between BPcalc and BPmeas for systolic, mean, or pulse pressure was determined with the technique proposed by Bland and Altman (4,5) where (BPmeas - BPcalc) is plotted on the y-axis versus the average of BPcalc and BPmeas values on the x-axis. The bias (mean difference between BPcalc and BPmeas), precision (SD of the bias), and limits of agreement (bias ± 2 SD) were determined (4–6).
If the limits of agreement were smaller than the threshold of clinical relevance as suggested by the Association for the Advancement of Medical Instrumentation (AAMI), to be 5 mm Hg ± 8 SD (7), the two methods were considered to be in agreement and, therefore, interchangeable. As suggested by Bland and Altman (5) to determine consistency of the bias, precision and limits of agreement, the 95% confidence interval (CI) was determined for each of these indices.
Phase 3
We used the first 50 readings of ear pulse oximeter width (WidthEar) and measured BP (BPmeas) to calibrate the intercept (a).
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The results from this equation would be 50 values for the intercept (a). The average value of these 50 readings would be used to determine the intercept (
). The calibrated intercept () was used in equation (2) instead of (a) to calculate BP for each patient (BPcalc).
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where i = systolic BP, mean BP, and pulse pressure, and (b) was the slope values derived from the first 10 cases (i.e., slope (b) values were 2.23, 1.33, and 1.35 for systolic BP, mean BP, and pulse pressure respectively). The analyses in phase 2 were repeated.
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Results |
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Phase 1
The study population had a mean age of 64 ± 9 yr, a mean height of 171 ± 7.8 cm, a mean weight of 81.4 ± 20.7 kg, and underwent CABG. The comparison of the raw data of pulse oximeter waveform variables of ear and finger with the arterial BP waveform reveal that the WidthEar has an obvious relationship to BPmeas as shown in Figure 1. Using 41,293 measurements collected from the first 10 patients, the linear regression correlation of the WidthEar had the best correlation with the BPmeas as shown in Figure 2.
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The average correlation (± SD) between WidthEar and BPmeas was 0.8 ± 0.1 for systolic BP, mean BP, pulse pressure and 0.76 ± 0.1 for diastolic BP. The range of correlation values for systolic BP, mean BP, pulse pressure, and diastolic BP were 0.66 to 0.96, 0.64 to 0.96, 0.6 to 0.96, and 0.43 to 0.96, respectively. The correlation coefficient (r value) for AreaEar and BPmeas was 0.25, and for AmpEar and BPmeas it was 0.31. Features extracted from finger plethysmographic waveforms demonstrated low correlation with measured BP (BPmeas). The r values were -0.1, 0.1, and 0.3 for WidthFinger, AreaFinger, and AmpFinger respectively.
Using simple linear regression, the intercept (a) and slope (b) values were determined using equation (1). For systolic BP, mean BP, and pulse pressure respectively, the mean intercept (a) values (± SD) were -30.06 ± 82.86, -8.14 ± 52.52, and -30.11 ± 49.71 and the mean slope (b) values (± SD) were 2.23 ± 1.13, 1.33 ± 0.68, and 1.35 ± 0.74.
Phase 2
On the next 10 patients using 62,077 measurements, BPcalc was determined by equation (2) based on the slope (b) and intercept (a) values generated by equation (1) between WidthEar and systolic BP, mean BP, and pulse pressure of BPmeas.
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where i = systolic BP, mean BP, and pulse pressure. Assessment of agreement between BPcalc and BPmeas was done using the Bland and Altman technique. The bias and precision were too large to be clinically useful: -8.96 mm Hg and 47.94 for systolic BP, -5.04 mm Hg and 29.47 for mean BP, and -8.18 mm Hg and 30 for pulse pressure, respectively, as shown in Table 1.
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Phase 3
After calibration the resulting bias, precision, and limits of agreement were -2.6, 15.9, and 29.2 to -34.4 mm Hg for systolic BP (Fig. 3), -1.88, 10.09, and 18.3 to -22.06 mm Hg for mean BP (Fig. 4) and -1.28, 9.94, and 18.6 to -21.16 mm Hg for pulse pressure (Fig. 5). The CI of the bias for each of these measurements is provided in Table 1.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Frequent measurement of arterial BP is a critical part of monitoring anesthetized or seriously ill patients. In clinical practice, BP measured by different techniques often yields significantly different values. For example, Bruner et al. (8) compared several methods of BP measurements and concluded that the direct method correlated poorly with indirect ones; so common are these inconsistencies that some investigators have declared "Blood pressure is a function of the way it is measured." The use of an intraarterial cannula for continuous measurement of BP is a widely accepted technique for monitoring during anesthesia and in intensive care units. It is regarded as accurate and indispensable in many situations (9).
However, the insertion of an intraarterial cannula is time consuming, may cause discomfort, and carries a risk of morbidity including hematoma and (rarely) thrombosis and infection (10). In view of these problems, several methods to measure BP noninvasively and continuously have been attempted. The Finapres (Ohmeda; Helsinki, Finland), which is no longer available, measures BP based on the arterial volume clamp method described by Penaz (11). A number of clinical studies have shown that Finapres has only limited clinical usefulness because of occasional large discrepancies between the Finapres and standard BP monitors (12,13). Arterial tonometry uses a two transducer system, to measure BP continuously (14). Some studies have shown good agreement between arterial tonometry and invasive arterial BP (15–18).
In 1987 it was noted intraoperatively that the loss of the audio and visual oximeter (Nellcor Pulse oximeter Model N-100; Nellcor, Pleasanton, CA) display correlated with the systolic BP obtained by Doppler flowmeter when the Doppler and pulse oximeter probes were on the same extremity (19).
Pulse plethysmography has also been used to estimate systolic BP. A manual BP cuff was placed on the same extremity as the pulse oximeter probe and the pressure was recorded at disappearance and reappearance of the oximeter waveform display during cuff inflation and deflation, which approximates the systolic BP (20). Systolic BP was measured in previous studies by pulse oximetry, Doppler method, an intraarterial cannula, and Korotkoff sounds. The BP data were recorded when the pressure was neither increasing nor decreasing. When pulse oximetry was compared with all other methods, the best correlation was found with the Doppler technique(r = 0.996) and the poorest correlation was found with the intraarterial cannula(r = 0,88). It is important to note that the direct methods measure pressure, whereas the indirect methods deal with the flow and volume changes. In addition, the sites at which the pressure is measured are not identical between methods (21). These previous studies did not estimate BP on a beat-to-beat basis; furthermore, they only estimated the systolic BP.
This study is an effort to understand the relationship between pulse oximeter waveforms of the ear and the finger and the BP waveforms (systolic BP, mean BP, diastolic BP, and pulse pressure). Our study populations consisted of inherently unstable cardiac patients scheduled for elective CABG who had diseased circulatory systems and were subjected to different vasoactive, vasodilator, and inotropic medications, resulting in extreme fluctuations in BP. The BP data were recorded during periods of fluctuation and changes in blood pressure (e.g., induction of anesthesia, skin incision, sternotomy, lifting of the heart, coming off bypass) to see how the pulse oximeter waveforms can relate to changes in BP readings. It is clear that there is a correlation between WidthEar and Bpmeas. This may be related in part to the fact that the ear is thought to be less sensitive to changes in sympathetic tone and vasoconstrictive stimuli (22).
The wide range (0.6 to 0.96) of the correlation between ear width and the systolic BP, mean BP, and pulse pressure may be related to arrhythmia and/or decreased preload (hypovolemia) where there was obvious respiratory variation.
Our attempt to develop a clinically useful method of noninvasive BP determination was only partly successful. Our bias was as shown in Table 1, but our SD was too large according to (AAMI) recommendations. In addition there is a requirement for a calibration period. The standards of the AAMI recommend that maximal bias of noninvasive BP obtained from at least 85 patients should not exceed 5 mm Hg ± 8 SD from a noninvasive reference method (7). Unfortunately, this criterion is not readily applicable in perioperative settings because these guidelines were intended for evaluating BP instruments used in outpatient clinics. In perioperative settings, an invasive reference standard is usual (23).
To develop a clinically useful method of noninvasive beat-to-beat BP determination, further investigation of pulse oximeter waveform correction is warranted. For example, a correction for heart rate (as a patient with heart rate of 100 bpm will have a smaller ear pulse oximeter width than a patient with heart rate of 60 bpm) may significantly improve pulse oximeter-BP correlation. It is our hope that this research will encourage further investigation of the pulse oximeter waveform to explore the other uses of pulse oximetry beyond determination of oxygen saturation.
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Acknowledgments |
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We are grateful to Stacey Shelley, BSN, BA for her valuable editorial advice and we thank Dr. John P. Concato for his advice on statistical analysis.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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- Yoshiya I, Shimada Y, Tanaka K. Spectrophotometric monitoring of arterial oxygen saturation in the fingertip. Med Biol Eng Comput 1980; 18: 27–32.[Web of Science][Medline]
- Yelderman M, New W Jr. Evaluation of pulse oximetry. Anesthesiology 1983; 59: 349–61.[Web of Science][Medline]
- Bernardi L, Radaelli A, Solda PL, et al. Autonomic control of skin microvessels: assessment by power spectrum of photoplethysmographic waves. Clin Sci 1996; 90: 345–55.[Medline]
- Bland JM, Altman DG. Measurement in medicine: the analysis of method comparison studies. Statistician 1983; 32: 307–17.[Web of Science]
- Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307–10.[Web of Science][Medline]
- LaMantia KR, O’Connor T, Barash PG. Comparing methods of measurement: an alternative approach. Anesthesiology 1986; 72: 781–83.
- Proposed standard for electronic or automated sphygmomanometers. Arlington, VA: Association for the Advancement of Medical Instrumentation, 1992.
- Bruner JMR, Krenis LJ, Kunsman JM, et al. Comparison of direct and indirect methods of measuring arterial blood pressure. Med Instrum 1981; 15: 11–21.[Web of Science][Medline]
- Slogoff S, Keats AS, Arlund C. On the safety of radial artery cannulation. Anesthesiology 1983; 59: 42–57.[Web of Science][Medline]
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Mangano DT, Hickey RF. Ischemic injury following uncomplicated radial artery catheterization. Anesth Analg 1979; 58: 55–7.
[Free Full Text] - Penaz J. Photoelectric measurement of blood pressure, volume, and flow in the finger. In: Albert R, ed. Digest of the 10th International Conference of Medical and Biological Engineering. Dresden: International Federation for Medical/Biological Engineering, 1973: 104.
- Gibbs NM, Larach DR, Derr JA. The accuracy of Finapres noninvasive mean arterial pressure measurements in anesthetized patients. Anesthesiology 1991; 74: 647–52.[Web of Science][Medline]
- Silke B, McAuley D. Accuracy and precision of blood pressure determination with the Finapres: an overview using re-sampling statistics. J Hum Hypertens 1998; 12: 403–9.[Web of Science][Medline]
- Kemmotsu O, Ueda M, Otsuka H, et al. Arterial tonometry for noninvasive, continuous blood pressure monitoring during anesthesia. Anesthesiology 1991; 75: 333–40.[Web of Science][Medline]
-
Weiss BM, Spahn DR, Rahmig H, et al. Radial artery tonometry: moderately accurate but unpredictable technique of continuous noninvasive arterial pressure measurement. Br J Anaesth 1996; 76: 405–11.
[Abstract/Free Full Text] - DeJong JR, Ros HH, DeLange JJ. Noninvasive continuous blood pressure measurement during anesthesia: a clinical evaluation of a method commonly used in measuring devices. Int J Clin Monit Comput 1995; 12: 1–10.[Medline]
- Kemmotsu O, Ohno M, Takita K, et al. Noninvasive, continuous blood pressure measurement by arterial tonometry during anesthesia in children. Anesthesiology 1994; 81: 1162–8.[Web of Science][Medline]
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Kemmotsu O, Ueda M, Otsuka H, et al. Blood pressure measurement by arterial tonometry in controlled hypotension. Anesth Analg 1991; 73: 54–8.
[Abstract/Free Full Text] -
Wallace C, Barker D, Apert C, et al. Comparison of blood pressure measurement by Doppler and by pulse oximetery techniques. Anesth Analg 1987; 66: 1018–19.
[Free Full Text] - Vegfors M, Tryggvason B, Sjoberg F, Lennmarken C. Assessment of peripheral blood flow using a pulse oximeter. J Clin Monit 1990; 6: 1–4.[Medline]
- Talke P, Nichols RJ, Traber DL. Does measurement of systolic blood pressure with a pulse oximeter correlate with conventional methods? J Clin Monit 1990; 6: 5–9.[Web of Science][Medline]
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Awad AA, Ghobashy MA, Ouda W, et al. Different responses of ear and finger pulse oximeter waveform to cold pressor test. Anesth Analg 2001; 92: 1483–6.
[Abstract/Free Full Text] -
Mantha S, Roizen MF, Fleisher LA, et al. Comparing methods of clinical measurement: reporting standards for Bland and Altman analysis. Anesth Analg 2000; 90: 593–602.
[Abstract/Free Full Text]
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