Anesth Analg 2001;92:1364-1369
© 2001 International Anesthesia Research Society
CARDIOVASCULAR ANESTHESIA
Pulmonary Arterial Pressure Can Be Estimated by Transesophageal Pulsed Doppler Echocardiography
Shinji Kawahito, MD, PhD,
Hiroshi Kitahata, MD, PhD,
Katsuya Tanaka, MD, PhD,
Junpei Nozaki, MD, and
Shuzo Oshita, MD, PhD
Department of Anesthesiology, Tokushima University School of Medicine, Kuramoto, Tokushima, Japan
Address correspondence and reprint requests to Dr. Shinji Kawahito, Department of Anesthesiology, Tokushima University School of Medicine, 3-18-15 Kuramoto, Tokushima, 770-8503, Japan Address e-mail to kawahito{at}pb4.so-net.ne.jp
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Abstract
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We examined whether pulmonary arterial pressure can be estimated on the basis of pulmonary arterial flow velocity determined via intraoperative pulsed Doppler transesophageal echocardiography (TEE) in 20 patients undergoing cardiac surgery. Standard pulmonary artery measurements were taken as well. Measurements were taken before sternotomy, after pericardiotomy, after cardiopulmonary bypass, and after sternum closure. The variables obtained by TEE included preejection period (PEP), acceleration time (AT), right ventricular ejection time (RVET), and R-R interval (RR). Five ratios were calculated as indices of pulmonary arterial pressure—PEP/AT, PEP/RVET, AT/RVET, PEP/
RR, and AT/RR—and were compared with pulmonary artery catheterization findings, i.e., systolic pulmonary arterial pressure (sPAP), log sPAP, mean PAP (mPAP), and log mPAP. Before sternotomy, PEP/AT, PEP/RR, and AT/RR showed significant correlation with all pulmonary artery catheterization values. AT/RVET showed correlation with all pulmonary artery values except log mPAP. PEP/AT showed the closest correlation with sPAP (r = 0.771) and log sPAP (r = 0.789). PEP/AT also showed close correlation with mPAP (r = 0.764) and log mPAP (r = 0.777). Significant agreement between sPAP and mPAP values calculated from a regression equation and values measured via pulmonary artery catheter was observed by plotting the differences against the mean values of the two measurements. We therefore conclude that noninvasive estimation of pulmonary arterial pressure is feasible via intraoperative TEE when sternotomy is not involved.
Implications: Accurate measurement of pulmonary arterial pressure has generally required cardiac catheterization; noninvasive intraoperative estimation of pulmonary arterial pressure has been an important clinical challenge for anesthesiologists. We demonstrated that pulsed Doppler transesophageal echocardiography can be used to estimate intraoperative pulmonary arterial pressure.
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Introduction
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Although diagnosis of pulmonary hypertension by noninvasive methods is considered difficult, a number of transthoracic echocardiography (TTE) techniques have been reported for noninvasive assessment of pulmonary arterial pressure (PAP). Several M-mode echocardiographic techniques, including analysis of the pulmonary valve (1), the right ventricular cavity (2), and the right ventricular wall (3), have been proposed. However, because each of these methods requires images that are difficult to obtain or measure, patients with increased PAP may still escape detection.
Many investigators are now applying continuous or pulsed Doppler echocardiography to estimate PAP, and the usefulness of such methods is widely recognized. Continuous-wave Doppler measurement of peak velocity of the tricuspid regurgitation peak jet has been used to estimate right ventricular systolic pressure (4–7). Although this is generally a good technique for estimating systolic PAP, problems may be encountered in patients with a poorly defined tricuspid regurgitant signal or with unusually high right atrial pressure. In addition, pulsed Doppler flow velocity measurements of the pulmonary artery have been used to estimate PAP (7–15), and a number of qualitative and quantitative assessments based on pulsed Doppler TTE have been reported. However, there have been no reports on whether transesophageal echocardiography (TEE) is as reliable as TTE for estimating PAP. We therefore investigated whether pulsed Doppler TEE can be used to estimate intraoperative PAP.
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Methods
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The study protocol was approved by the Ethics Committee on Human Study of Tokushima University School of Medicine, and written informed consent was obtained from all subjects. We studied 20 patients scheduled for elective cardiac surgery (13 men and 7 women, ranging in age from 43 to 75 yr, with a mean age of 58.6 ± 8.6 yr). Operations performed included mitral valve replacement (n = 2), mitral valvuloplasty (n = 5), aortic valve replacement (n = 5), mitral valve replacement plus aortic valve replacement (n = 1), closure of an endocardial cushion defect (n = 2), and coronary artery bypass grafting (n = 5). Absence of normal sinus rhythm was the exclusion criterion.
A cannula was inserted into the radial artery for measurement of arterial pressure. Anesthesia was induced by combined IV administration of fentanyl (200–500 µg) and thiamylal (50–200 mg). Muscle relaxation was achieved with IV vecuronium (0.15 mg/kg). After the induction of anesthesia and tracheal intubation, a pulmonary artery catheter was inserted via the right internal jugular vein, and a 5-MHz TEE probe (UST-5233S-5; Aloka, Tokyo, Japan) was inserted into the esophagus and attached to a color Doppler imaging system (SSD-830; Aloka). The end-tidal CO2 level was monitored by capnography, and respiration was controlled such that the level of PaCO2 was maintained between 35 and 40 mm Hg. Anesthesia was maintained by continuous injection of fentanyl (total, 30–100 µg/kg) and nitrous oxide–oxygen-sevoflurane or oxygen-sevoflurane.
Doppler images were obtained via the upper esophageal transverse pulmonary artery view. The pulsed Doppler sampling volume was carefully positioned in the center of the main trunk of the pulmonary artery, and the pulmonary artery flow velocity was recorded during ventilatory cessation on an S-VHS videotape and line recorder at a speed of 100 mm/s. A single investigator blinded to all other data performed the analysis. Doppler measurements were averaged over 3 consecutive cardiac cycles. Measurements were then made to determine hemodynamic status at various time points before and after cardiopulmonary bypass. The following measurements were taken before sternotomy, after pericardiotomy, after cardiopulmonary bypass, and after sternum closure: preejection period (ms) (PEP = the time interval from onset of the electrocardiographic Q wave to the initial systolic upward deflection of the pulmonary artery flow velocity curve), acceleration time (ms) (AT = the time interval between the onset and peak of pulmonary flow velocity), right ventricular ejection time (ms) (RVET = the time interval from the onset to termination of the systolic pulmonary flow velocity, i.e., return of the velocity curve to baseline), and R-R interval (ms) (RR = the time interval of R wave of electrocardiogram) (Fig. 1). Three ratios—PEP/AT, PEP/RVET, and AT/RVET—were calculated for each cardiac cycle. Further, PEP and AT were corrected for heart rate by dividing the respective value by the square root of the proceeding RR of the electrocardiogram. Thus, a total of five ratios were calculated as indices of PAP—PEP/AT, PEP/RVET, AT/RVET, PEP/
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Figure 1. Measurement of pulmonary arterial flow velocity. The left panel shows the two-dimensional upper esophageal transverse pulmonary artery view. The pulsed Doppler sampling volume is located in the center of the main trunk of the pulmonary artery. The right panel shows the pulsed Doppler wave form of pulmonary arterial blood flow velocity. The Doppler signal and electrocardiogram are recorded simultaneously. Preejection period (PEP), acceleration time (AT), and right ventricular ejection time (RVET) were measured as shown in this figure. AO = aorta; PA = pulmonary artery.
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equation
, and AT/equation
—and the respective values were compared with simultaneous pulmonary arterial catheter measurements of systolic PAP (sPAP), logarithm of sPAP (log sPAP), mean PAP (mPAP), and logarithm of mPAP (log mPAP). Correlations between the Doppler-derived indices and the standard hemodynamic variables were examined.
Simple regression analysis was performed to estimate PAP from the Doppler-derived PEP/AT. On the basis of some of our findings (given in Results), PEP/AT was chosen as the variable on which to estimate PAP by regression analysis. The accuracy of Doppler-derived estimated PAP in comparison with PAP measured via pulmonary arterial catheter (measured PAP) was tested by the Bland and Altman method (16). Bias between methods was determined as the mean difference between estimated PAP and measured PAP. The precision of PAP measurements is given by the limits of agreement (2 SD of the mean difference between methods). In addition, correlation analysis was performed between values obtained by the two methods. Wilcoxon’s signed rank test was used to compare the mean difference with zero, and a probability value of <0.05 was considered significant.
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Results
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Recording pulmonary arterial flow was successful in all patients before sternotomy; however, it was not possible after pericardiotomy, cardiopulmonary bypass, or sternum closure in five patients. Thus, a total of 65 measurements were made, and all index values were taken from these 65 measurements. Correlations between indices are shown in Table 1. Before sternotomy, PEP/AT, PEP/
equation
, and AT/equation
showed significant correlation with all pulmonary artery catheterization values. AT/RVET showed correlation with all pulmonary artery values except log mPAP. PEP/AT and sPAP (r = 0.771) and log sPAP (r = 0.789) were most closely correlated, and PEP/AT and mPAP (r = 0.764) and log mPAP (r = 0.777) were also closely correlated (Fig. 2). The correlation coefficients improved slightly when these ratios were compared with the logarithms of sPAP and mPAP. After pericardiotomy, no index was significantly correlated with PAP; after cardiopulmonary bypass, no index was significantly correlated with PAP. After sternum closure, PEP/
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Figure 2. Correlation and linear regression analysis of PEP/AT and sPAP (left upper), log sPAP (left lower), mPAP (right upper), and log mPAP (right lower) before sternotomy. Significant correlations are observed. PEP = preejection period; AT = acceleration time; sPAP = systolic pulmonary arterial pressure; log sPAP = logarithm of sPAP; mPAP = mean pulmonary arterial pressure; log mPAP = logarithm of mPAP.
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equation
and AT/equation
showed significant correlation with PAP, but ratios such as PEP/AT, which showed strong correlation before sternotomy, did not show significant correlation after sternotomy.
Differences between methods and correlation analysis before sternotomy are shown in Figures 3 and 4. The mean difference between measured sPAP and estimated sPAP from PEP/AT was 0.23 mm Hg (2 SD of the difference between methods = 16.98 mm Hg). The mean difference between measured mPAP and estimated mPAP from PEP/AT was 0.10 mm Hg (2 SD of the difference between methods = 11.76 mm Hg) (Fig. 3). Correlation analysis between estimated sPAP and measured sPAP showed a close linear relationship (r = 0.778). The correlation coefficient for estimated mPAP and measured mPAP was 0.747 (Fig. 4). Estimated sPAP and mPAP from PEP/AT did not differ significantly from measured sPAP and mPAP. An improved fit was observed between the estimated sPAP and the measured sPAP.
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Figure 3. Difference between the two measurements against their mean. Left panel, Bland-Altman plot of measured sPAP and estimated sPAP (from PEP/AT). Right panel, Bland-Altman plot of measured mPAP and estimated mPAP (from PEP/AT). PEP = preejection period; AT = acceleration time; sPAP = systolic pulmonary arterial pressure; mPAP = mean pulmonary arterial pressure.
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Figure 4. Correlation between the measured PAP and estimated PAP (from PEP/AT). Left panel, correlation between the measured sPAP and estimated sPAP (from PEP/AT). Right panel, correlation between the measured mPAP and estimated mPAP (from PEP/AT). PEP = preejection period; AT = acceleration time; sPAP = systolic pulmonary arterial pressure; mPAP = mean pulmonary arterial pressure.
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Ten randomly selected pulsed Doppler recordings were used to assess interobserver and intraobserver variability in the measurement of PEP and AT. Interobserver variabilities in the measurement of PEP and AT were 4.9% ± 2.7% and 8.9% ± 4.1%, respectively, with intraobserver variabilities of 4.7% ± 2.1% and 6.3% ± 3.8%, respectively.
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Discussion
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Accurate measurement of PAP has generally required cardiac catheterization. Noninvasive intraoperative estimation of PAP is thus an important clinical challenge for anesthesiologists. TEE is used during surgery to assess left ventricular function, myocardial ischemia, valvular function, preload, and cardiac output (17–19). It is useful for estimating intracardiac pressure and evaluating intracardiac volume. Although the clinical usefulness of TTE as a noninvasive means of estimating PAP has been reported by several investigators (4–15), the efficacy of TEE for evaluation of intraoperative PAP on the basis of pulmonary arterial flow velocity has not been reported. Ours is the first reported investigation of the use of pulmonary arterial flow velocities obtained by TEE for intraoperative estimation of PAP. In this study, the pulmonary arterial flow velocity ratios obtained via TEE showed significant correlation with PAP before sternotomy and were thus considered useful indices. PEP/AT correlated most strongly with sPAP and mPAP. Our results are in agreement with those of Isobe et al. (8), who found good correlation between PEP/AT and both sPAP and mPAP by use of TTE. Moreover, the correlation coefficients improve when a logarithmic function is applied. In this study, the correlation coefficients did indeed improve slightly when ratios were compared with the logarithms of sPAP and mPAP.
Many investigators have applied continuous or pulsed Doppler TTE to evaluate PAP. Continuous-wave Doppler measurement of peak velocity in the tricuspid regurgitation jet has been used to estimate the systolic pressure gradient between the right ventricle and the right atrium (4–7). Prediction of right ventricular systolic pressure should be possible in patients with tricuspid regurgitation by adding the Doppler-determined transtricuspid gradient to the right atrial pressure (estimated clinically from central venous pressure). In the absence of pulmonary stenosis, right ventricular systolic pressure is equivalent to pulmonary artery systolic pressure. However, in some patients with increased PAP, it may be difficult to record the tricuspid regurgitation jet, and in other patients with normal PAP, the tricuspid regurgitation jet may be absent.
Pulsed Doppler flow velocity measurements of the pulmonary artery have also been used to estimate PAP (7–15). With regard to TTE, Kitabatake et al. (9) measured right ventricular outflow tract Doppler flow velocity and reported a very strong negative correlation between AT/RVET and log mPAP (r = 0.90). Other investigators also report AT/RVET as a good predictor of PAP (10,11). Chan et al. (7), Kosturakis et al. (12), Dabestani et al. (13), and Marchandise et al. (14) found that AT showed good correlation with both sPAP and mPAP and that correction for RVET did not improve the correlation. The discrepancy seems to be caused by inaccuracy in RVET measurements. With regard to RVET, we found that the end of systole was somewhat difficult to ascertain by Doppler echocardiography, especially in the presence of turbulence. Avoiding the inaccuracy of RVET measurement, Isobe et al. (8) found PEP/AT to yield the best correlation with mPAP (r = 0.89); this accords with our findings.
There have been many reports on factors that influence the indices of pulmonary arterial flow velocity. PEP is thought to be influenced by four basic factors: cardiac preload, cardiac afterload, contractility of the myocardium, and ventricular electrical activation (15). Although it is not known which factor is the major determinant of PEP, the presence of right ventricular dysfunction or of pulmonary hypertension may affect this variable. Myocardial contractility appears to be related to AT as well as afterload. In addition, PEP and AT are also influenced by heart rate (7,15). By correcting each of the indices of pulmonary arterial flow velocity for these factors, the ratios could be used effectively, and the relationships between pulmonary arterial flow velocity and PAP generally remained constant with cardiac output changes. PEP/AT is reported to predict PAP, even in a low output state (8). After pericardiotomy, however, these relationships completely disappear. Even recording suitable pulmonary arterial flow was not feasible in five of our patients. It seems likely that these remarkable changes resulted from changes in the anatomic position (the axis, for example) of the heart, in the compliance of the pulmonary artery as a sampling point, and in the transmural pressure. For this reason, PEP/AT, which was a very reliable index before sternotomy, may have lost its significant correlation with PAP after sternal closure.
Different investigators have used different Doppler sampling sites to evaluate patients with pulmonary hypertension. The proper sampling site is very important for preventing eddy currents in patients with pulmonary hypertension and the mixing of signals caused by systolic fluttering of the pulmonic cusp. Each index of pulmonary arterial flow velocity is reportedly affected by the site of the sampling volume (20). In this study, we recorded pulmonary arterial flow in the center of the main trunk of the pulmonary artery, as in reported TTE studies (12–14). For TEE, the more suitable sampling point seems to be the center of the main trunk of the pulmonary artery rather than in the artery just distal to the pulmonary valve, where cardiac output is usually measured (19).
Although our sample was small and our correlations were positive but not optimally strong, our findings indicate that before sternotomy in patients undergoing elective cardiac surgery, pulsed Doppler TEE is useful for estimation of PAP. A good correlation with PAP was achieved by PEP/AT, and significant agreement between the PAP estimated from the PEP/AT and the measured PAP was observed in the Bland and Altman (16) analysis. Our study was undertaken in cardiac surgery patients, in whom PAP is measured invasively as a matter of course. However, there are many patients scheduled for noncardiac surgeries (e.g., vascular surgery); for these patients, invasive procedures are ill-advised, but their PAP should be monitored. These patients include the older patients and those with heart disease, including pulmonary hypertension. Pulsed Doppler TEE determination of PAP will be best applied in such high-risk patients.
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Footnotes
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Presented in part at the Annual Meeting of the American Society of Anesthesiologists, Orlando, FL, October 20, 1998.
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Accepted for publication February 2, 2001.
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Abstract
Introduction
