Measurement of cardiac output by transoesophageal echocardiography: a comparison of two Doppler methods with thermodilution

Comparison of Cardiac Output of Both 2-Dimensional and 3-Dimensional Transesophageal Echocardiography With Transpulmonary Thermodilution During Cardiac Surgery

OBJECTIVES

To compare agreement and variability of cardiac output measurement of 2-dimensional (2D) and 3D transesophageal echocardiography (TEE) with thermodilution before and after bypass.

DESIGN

Prospective observational study.

SETTING

Two tertiary hospitals.

INTERVENTIONS

Cardiac output (CO) was measured simultaneously with thermodilution and TEE by multiplying either the left ventricular outflow tract area (LVOTA) or aortic valve area (AVA), the velocity-time integral (VTI) of flow at the same site, and heart rate. The LVOTA was calculated using diameter for 2D TEE. Planimetry was used for 3D TEE. The AVA was measured using planimetry.

PARTICIPANTS

The study comprised 82 adult patients undergoing coronary or valve surgery.

MEASUREMENTS AND MAIN RESULTS

One hundred fifty-four complete sets of measurements were obtained (82 prebypass and 72 postbypass). All TEE methods had acceptable correlation and absence of proportional or fixed bias except for the left ventricular outflow tract (LVOT) VTI modal trace method, which had poor correlation and proportional but not fixed bias (regression coefficient [95% confidence interval], bias [percentage of mean CO]): 2D LVOT VTI modal trace 0.67 (0.54-0.80), -36.4%; 2D LVOT VTI outer edge trace 0.96 (0.80-1.12), -15.3%; 2D AVA planimetry 0.96 (0.75-1.18), +4.9%; 3D LVOT area planimetry 1.18 (0.96-1.41), +0.8%; 3D AVA planimetry 1.20 (0.93-1.46), +0.4%. All TEE methods had wide levels of agreement compared with thermodilution (-3.94 to +0.23 L/min, -2.83 to +1.28 L/min, -2.23 to +2.73 L/min, -2.35 to +2.42 L/min, and -2.57 to +2.61 L/min, respectively). Measurement variability was superior for all TEE methods compared with thermodilution before but not after bypass.

CONCLUSIONS

Although limits of agreement of CO measurement with 3D TEE and thermodilution are wide, 2D planimetry of the AVA and continuous wave Doppler may be substituted for thermodilution before and after bypass.

Is the Nexfin finger cuff method for cardiac output measurement reliableduring coronary artery bypass grafting? A prospective comparison with the echocardiography and FloTrac/Vigileo methods

BACKGROUND/AIM

The aim of the current study was to assess the accuracy of cardiac output (CO) measurements obtained by the Nexfin finger cuff method as compared with the FloTrac/Vigileo and echocardiography methods in coronary artery bypass grafting (CABG) patients.

MATERIALS AND METHODS

First-time elective CABG patients were prospectively enrolled in this study and divided into three groups according to CO measurement method. CO measurements were performed simultaneously by three different contributors and were collected by the fourth one 24 h postoperative in the intensive care unit (ICU). Data were statistically analyzed.

RESULTS

Seventeen female and 13 male patients between 42 and 78 years of age (with a mean of 56 ± 4) were the subjects of this study. The mean CO measurements were 5.9 ± 1.4 L/min, 5.8 ± 1.1 L/min, and 6.0 ± 1.1 L/min for the Nexfin, FloTrac/Vigileo, and echocardiography methods, respectively (P > 0.05). The correlation values between Nexfin and FloTrac/Vigileo, Nexfin and echocardiography, and FloTrac/Vigileo and echocardiography were r = 0.445, r = 0.377, and r = 0.384, respectively (P < 0.05).

CONCLUSION

Nexfin yielded results comparable to those obtained with FloTrac/Vigileo and echocardiography for the postoperative CO assessment of CABG patients. Nexfin may be used in uncomplicated, hemodynamically stable patients in ICU as a reliable and totally noninvasive method of CO measurement.

Monitoring cardiac function: echocardiography, pulse contour analysis and beyond

Haemodynamic monitoring has developed considerably over the last decades, nowadays comprising a wide spectrum of different technologies ranging from invasive to completely non-invasive techniques. At present, the evidence to continuously measure and optimise stroke volume, that is, cardiac output, in order to prevent occult hypoperfusion in the perioperative setting and consequently to improve patients' outcome is substantial. Surprisingly, there is a striking discrepancy between the developments in advanced haemodynamic monitoring combined with evidence-based knowledge on the one hand and daily clinical routine on the other hand. Recent trials have shown that perioperative mortality is higher than anticipated, emphasising the need for the speciality of anaesthesiology to face the problem and to translate proven concepts into clinical routine to improve patients' outcome. One basic principle of these concepts is to monitor and to optimise cardiac function by means of advanced haemodynamic monitoring, using echocardiography, pulse contour analysis and beyond.

Cardiac dysfunction investigation in prehypertension

To study the possible cardiac function alternation in hypertension, 13 cardiac function parameters such as blood pressure (BP), cardiac output (CO), ejection time (ET) and stroke volume (SV), etc. were measured in 898 subjects. The subjects were grouped into 3 groups by blood pressure, namely: normotension, prehypertension and hypertension group. Statistic analyses showed that in prehypertension subjects, peak velocity and cardiac output increased, while the systemic vascular resistance index had no significant increase compared with normotensive. Peak velocity, mean pressure gradient and velocity time integral in prehypertension were significantly correlated with systolic blood pressure, however, no correlation was found in either normotension or hypertension subjects. The results suggest that increasing cardiac output and peak velocity occurred at the phase of prehypertension, which may conduce to the elevation of blood pressure.

Noninvasive Doppler ultrasonography for assessing cardiac function: can it replace the Swan-Ganz catheter?

BACKGROUND

Cardiac function, including cardiac index (CI), traditionally has been measured by a pulmonary artery catheter (PAC). A noninvasive alternative for measuring cardiac function would offer obvious advantages.

METHODS

A prospective study of trauma and nontrauma patients was performed in a surgical intensive care unit over a 3-month period. CI was determined using both a standard PAC and a continuous-wave Doppler ultrasound (UTS). The study had 2 phases: phase I was nonblinded and phase II was blinded; the correlation between UTS- and PAC-derived CI was assessed.

RESULTS

A total of 120 paired measurements of CI were observed in 31 patients. The UTS-derived CI measurements showed agreement with PAC measurements in both phase I and phase II of the study with a bias of .06 L/min/m(2) +/- .4 L/min/m(2). Paired measurements correlated well in both phase I (r = .97, R2 = .95, P < .0001) and phase II (r = .93, R2 = .86, P < .0001) of the study.

CONCLUSIONS

Doppler UTS correlates well with PAC measurements of CI. This noninvasive modality is an accurate and safe alternative to PAC.

Transoesophageal echocardiography accurately detects cardiac output variation: a prospective comparison with thermodilution in cardiac surgery

BACKGROUND AND OBJECTIVE

Intraoperative Doppler ultrasound can be used to measure cardiac output by transoesophageal echocardiography. Recently, its reliability, when compared to the thermodilution technique, has been questioned. The purpose of this study was to compare intraoperative changes in cardiac output measured by echo-Doppler and by thermodilution in cardiac surgery. We also assessed the agreement between the techniques.

METHODS

Fifty cardiac surgical patients (38 male, 12 female, mean age of 63.4 +/- 14.3 yr) were prospectively included after approval by the Ethics Committee of the Institution. Cardiac output was assessed by thermodilution, with 10 mL saline at 12 degrees C, and simultaneously and blindly by echo-Doppler in deep transgastric view with pulsed wave Doppler at the level of the left ventricular outflow tract. Matched thermodilution cardiac output and echo-Doppler cardiac output measurements were taken three times at the end of expiration, both pre- and post-cardiopulmonary bypass.

RESULTS

Echo-Doppler measurements were obtained in 44 patients (88%). In three patients, Doppler recordings could not be obtained adequately, and three developed left ventricular outflow tract obstruction after bypass. Bland-Altman analysis revealed a bias of 0.015 L min(-1), with narrow limits of agreement (-1.21 to 1.22 L min(-1)) and 29.1% error. Echo-Doppler was accurate (92% sensitivity and 71% specificity, P = 0.008 by receiver operating characteristic curves) for detecting more than 10% of change in thermodilution cardiac output. There were no complications related to the study.

CONCLUSIONS

The agreement between cardiac output by echo-Doppler and by thermodilution is clinically acceptable and transoesophageal echocardiography is a reliable tool to assess significant cardiac output changes in a population of selected patients.

Feasibility of preclinical cardiac output and systemic vascular resistance in HEMS in thoracic pain--the ultrasonic cardiac output monitor

BACKGROUND

Cardiac output (CO) and systemic vascular resistance (SVR) are important hemodynamic parameters in emergency patients and for clinical early goal-directed therapy. This study evaluated the feasibility of CO and SVR determination using preclinical continuous wave Doppler ultrasound in a helicopter emergency medical service (HEMS) on emergency patients presenting with or without thoracic pain as a pilot observational study.

METHODS

Forty-four consecutive medical emergency patients (62.8 +/- 22 years of age, 23 males) were classified at the scene as with (15 patients, 69 +/- 14 years of age, 40% male) or without (29 patients, 60 +/- 25 years of age, 59% male) thoracic pain by an emergency physician. Hemodynamic parameters were determined based on continuous wave Doppler noninvasively (USCOM, Sydney, Australia): stroke volume (SV), CO, cardiac index (CI), minute distance (MD), and SVR.

RESULTS

Noninvasive SV, MD, CO, CI, and SVR determination is feasible using preclinical ultrasound in HEMS. Thoracic pain patients had higher SVR (2,709 +/- 891 vs 1,499 +/- 661 dyne*sec*cm-5) and lower CO/CI (3.37 +/- 1.1 vs 5.06 +/- 2.9 L/min, CI: 1.67 +/- 0.58 vs 3.18 +/- 1.34 L/min/m2) as well as a reduced aortic minute distance (11.2 +/- 3.3 m/min vs 19.1 +/- 8 m/min, P = .001) than patients without thoracic pain. Highest cardiac outputs were measured during and within 30 minutes after seizures (n = 5, 7.5 +/- 3.05 L/min). The range of CO measured in six cardiopulmonary resuscitation patients was 2.7 to 12 L/min; the level of CO was not associated with the establishing of sustained circulation.

CONCLUSIONS

Determining SV, CO/CI, and SVR in different emergency situations in HEMS using rapid CW Doppler ultrasound is feasible. Thoracic pain patients have increased SVR and lower CO/CI and reduced aortic minute distance than do non-thoracic pain patients in the preclinical setting.

Effective systolic orifice area of the aortic valve: implications for Doppler echocardiographic cardiac output determinations

BACKGROUND

Substantial research using echocardiography has established that stroke volume (SV) or cardiac output (CO) can be measured non-invasively at the level of the aortic valve (AV) with high accuracy. Stroke volume is the product of the velocity time integral occurring at the sampling site and the effective systolic AV orifice area (AVOAeff). Nevertheless, a generally accepted method for the determination of AVOAeff is still lacking.

METHODS

Aortic valve OAeff was measured in 228 consecutive patients scheduled for coronary artery surgery. Two widely adopted methods were applied to approximate the constantly changing orifice area of the AV: (1) the circular orifice model (AVOA-CM), and (2) the triangular orifice model (AVOA-TM). Aortic valve OA-CM assumes the shape of a circle as an appropriately time averaged geometrical model, and AVOA-TM takes the shape of an equilateral triangle for granted.

RESULTS

The AV was easily imaged by echocardiography in both short- and long-axis views in all patients. Relying on AVOA-CM, AVOAeff was 3.49+/-0.77 cm2. AVOA-TM estimates were 2.80+/-0.55 cm2 (mean+/-SD). The results did not agree (bias analysis).

CONCLUSIONS

The echocardiographic measurement of SV or CO at the level of the AV has to be reconsidered.

Clinical evaluation of USCOM ultrasonic cardiac output monitor in cardiac surgical patients in intensive care unit

BACKGROUND

The USCOM ultrasonic cardiac output monitor (USCOM Pty Ltd, Coffs Harbour, NSW, Australia) is a non-invasive device that determines cardiac output by continuous-wave Doppler ultrasound. The aim of this study was to evaluate the accuracy of the USCOM device compared with the thermodilution technique in intensive care patients who had just undergone cardiac surgery.

METHODS

We conducted a prospective study in the 18-bed intensive care unit of a 600-bed tertiary referral hospital. Twenty-four mechanically ventilated patients were studied immediately following cardiac surgery. We evaluated the USCOM monitor by comparing its output with paired measurements obtained by the standard thermodilution technique using a pulmonary artery catheter.

RESULTS

Forty paired measurements were obtained in 22 patients. We were unable to obtain an acceptable signal in the remaining two patients. Comparison of the two techniques showed a bias of 0.18 and limits of agreement of -1.43 to 1.78. The agreement may not be as good between techniques at higher cardiac output values.

CONCLUSIONS

The USCOM monitor has a place in intensive care monitoring. It is accurate, rapid, safe, well-tolerated, non-invasive and cost-effective. The learning curve for skill acquisition is very short. However, during the learning phase the USCOM monitor measurements are rather 'operator dependent'. Its suitability for use in high and low cardiac output states requires further validation.

Transoesophageal echocardiography is unreliable for cardiac output assessment after cardiac surgery compared with thermodilution*

This randomised, single-blind, double-control study compared and established prospectively the best transoesophageal echocardiography methods for determining cardiac output in patients after cardiac surgery. Thirty patients undergoing coronary artery bypass grafting were included. Measurements were taken postoperatively, after stabilisation in the intensive care unit. Cardiac output was determined by transoesophageal echocardiography in randomised order through the aortic, mitral, and pulmonary valves, right and left ventricular outflow tracts, transgastric surface areas of the left ventricle and left ventricle two-dimensional volumes (Simpson's rules). 'Eyeball guessing' was done off-line. The best results were transaortic measurements using the triangular shape assumption of valve opening, but some values deviated considerably, and none of these approaches reached the limit of agreement set at 30% when compared to thermodilution. Eyeball guessing was comparable to the best transoesophageal echocardiography measurements. We conclude that transoesophageal echocardiography is an unreliable tool for determination of cardiac output in intensive care after cardiac surgery.

Effect of xenon anaesthesia on accuracy of cardiac output measurement using partial CO2rebreathing

Cardiac output (CO) determination based on partial CO(2) rebreathing has recently been introduced into clinical practice. The determination of flow is crucial for exact CO readings and the physical properties of xenon, i.e. high density and viscosity, may influence flow readings. This study compared echocardiography-derived CO measurements with the partial rebreathing method during total intravenous (TIVA) vs. xenon-based anaesthesia. Thirty-nine patients ASA physical status III undergoing aortic reconstruction were randomly assigned to receive either xenon (Xe, n = 20) or TIVA (T, n = 19) based general anaesthetic. Paired measurements were taken before xenon administration, after xenon administration, before and after clamping of the abdominal aorta and after declamping and at corresponding time points in the TIVA group. Data were analysed with a Bland-Altmann plot. Bias and precision were acceptable and comparable before xenon administration (T 0.54 +/- 0.92 l.min(-1) vs. Xe 0.11 +/- 1.1 l.min(-1)), but after xenon administration CO was largely overestimated by partial CO(2) rebreathing (T 0.04 +/- 0.91 l.min(-1) vs. Xe -4.0 +/- 2.1 l.min(-1)). In the TIVA group, bias and precision after declamping increased significantly (P < 0.01) compared to all time points except baseline. In its current application, the NICO cardiac output monitor appears to be inappropriate for determination of CO during xenon based anaesthesia.

Harvest of the radial artery for coronary artery surgery preserves maximal blood flow of the forearm

BACKGROUND

Use of the radial artery as a conduit for coronary artery surgery has increased dramatically. It has been assumed that blood flow to the forearm will not be compromised by its removal.

METHODS

Sixteen patients who had the left radial artery harvested for coronary surgery at least 3 months earlier were studied. The right radial artery was not harvested. The radial, ulnar, and brachial artery diameters and flows were measured using pulsed wave Doppler with a 15-MHz linear array transducer. Measurements were performed at rest, with the right radial artery compressed, and after ischemia with forearm exercise.

RESULTS

At rest, the (mean +/- SE) diameter of the left ulnar artery was consistently greater than the right (2.4 +/- 0.09 versus 2.1 +/- 0.09 mm, p = 0.001) as was flow (74 +/- 9.9 versus 48 +/- 8.5 mL/min, p = 0.005). There was no difference between diameters or flows in the brachial arteries. After compression of the radial artery, flow increased in the right ulnar artery from 39 +/- 8.0 to 72 +/- 17.6 mL/min (p = 0.019) without an increase in ulnar artery size and was not different from the left ulnar artery flow at rest (p = 0.440). After ischemic forearm exercise, flow increased in the two brachial arteries almost equally (left, 348 +/- 50; right, 371 +/- 63 mL/min).

CONCLUSIONS

Blood flow to the forearm and hand is not compromised by harvest of the radial artery.

Survey of observer variation in transesophageal echocardiography: comparison of anesthesiology and cardiology literature

OBJECTIVE

Transesophageal echocardiographic examination tends to be somewhat observer and experience dependent, and observer bias can arise easily when data are calculated and interpreted by unskilled, nonblinded, or single observers. The study plan was to see whether authors have adequately described how observer bias is minimized in their studies. Thus, a study was conducted systematically reviewing methods reported in transesophageal echocardio graphy articles in peer-reviewed anesthesiology journals versus those reported in peer-reviewed cardiology journals.

INTERVENTIONS

After MEDLINE searches of the literature published from 1997 through 1999, the authors investigated 56 anesthesiology reports and 56 randomly selected, year-matched cardiology reports. An 8-item questionnaire was developed that examined several factors: the number of observers and their experience levels, whether observers were blind to clinical data, whether low-quality images were excluded, the use of on-line or off-line analysis, and observer variability.

MAIN RESULTS

The analysis revealed inadequacies in reporting of important information that relates to bias and quality in 91.1% of anesthesiology and 98.2% of cardiology articles. Observer variability was not reported in 50.0% of the anesthesiology reports and 67.9% of the cardiology reports; however, difference between the 2 bodies of literature was not significant. The journal impact factor was significantly higher for the cardiology literature than for the anesthesiology literature (2.42 [0.386-10.893] v 1.07 [0.664-3.439]; median [range], p < 0.001).

CONCLUSION

Articles reviewed had at least some inadequacies in reporting the methods to minimize observer bias in both the anesthesiology and cardiology literature. Reporting methodology standards in TEE examinations remain to be established.

The effect of pericardial restraint, atrial pacing, and increased heart rate on left ventricular systolic and diastolic function in patients undergoing cardiac surgery

Baseline measurements of systolic and diastolic function performed after the induction of anesthesia may be compared with subsequent measurements acquired under different physical conditions such as open pericardium and different heart rate or rhythm. We acquired data from 21 patients undergoing coronary artery surgery. Combined echocardiographic and pulmonary artery catheter measurements were performed before and after pericardial opening, atrial pacing at the native rate, and atrial pacing 30 bpm faster. Indices of systolic function included fractional area change, afterload corrected fractional area change, and myocardial performance index; diastolic function included mitral inflow and pulmonary vein Doppler profiles, color M-Mode Doppler flow propagation velocity, instantaneous end-diastolic stiffness, and isovolumetric relaxation time. Hemodynamic indices included cardiac index, mean arterial, right atrial, and pulmonary capillary wedge pressures, and systemic vascular resistance index. There were no changes in measurements after opening of the pericardium or with institution of atrial pacing. With increased heart rate, there were no changes in systolic function, but instantaneous end-diastolic stiffness increased. Propagation velocity showed a paradoxical improvement with increased heart rate opposite to other trends. Beat fusion occurs with increasing heart rate for mitral inflow Doppler. We recommend that serial measurements are performed at a similar heart rate.

IMPLICATIONS

Pericardial restraint or the institution of atrial pacing do not alter left ventricular function, as assessed by pulmonary artery catheter and transesophageal echocardiography measurements. Diastolic (but not systolic) measurements showed inconsistency with increased heart rate.

Use of echocardiography for hemodynamic monitoring

OBJECTIVE

To assess the accuracy of echocardiography for hemodynamic monitoring.

DATA SOURCES

A computerized MEDLINE search was used with the following search headings: monitoring (physiologic and intra-operative) and both echocardiography and transesophageal echocardiography. A number of studies were obtained from the reference lists of cardiology reviews and textbooks.

STUDY SELECTION

Studies that were designed to assess the accuracy of hemodynamic monitoring.

DATA EXTRACTION

From the selected studies, the accuracy of different techniques for measuring preload and cardiac output was compared.

DATA SYNTHESIS

Hypovolemia can be detected accurately by measuring left ventricular end-diastolic area. At high preload, Doppler-based methods are more accurate, although further studies in critical care patients are needed. Cardiac output is best measured by measuring Doppler flow, preferably across the aortic valve.

CONCLUSIONS

Echocardiography can be used to make accurate hemodynamic measurements; however, training is required. Further studies are needed to validate these methods in the management of critically ill patients.