Transoesophageal echocardiography is unreliable for cardiac output assessment after cardiac surgery compared 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.

Noninvasive Hemodynamic Measurements During Neurosurgical Procedures in Sitting Position

BACKGROUND

Neurosurgical procedures in sitting position need advanced cardiovascular monitoring. Transesophageal echocardiography (TEE) to measure cardiac output (CO)/cardiac index (CI) and stroke volume (SV), and invasive arterial blood pressure measurements for systolic (ABPsys), diastolic (ABPdiast) and mean arterial pressure (MAP) are established monitoring technologies for these kind of procedures. A noninvasive device for continuous monitoring of blood pressure and CO based on a modified Penaz technique (volume-clamp method) was introduced recently. In the present study the noninvasive blood pressure measurements were compared with invasive arterial blood pressure monitoring, and the noninvasive CO monitoring to TEE measurements.

METHODS

Measurements of blood pressure and CO were performed in 35 patients before/after giving a fluid bolus and a change from supine to sitting position, start of surgery, and repositioning from sitting to supine at the end of surgery. Data pairs from the noninvasive device (Nexfin HD) versus arterial line measurements (ABPsys, ABPdiast, MAP) and versus TEE (CO, CI, SV) were compared using Bland-Altman analysis and percentage error.

RESULTS

All parameters compared (CO, CI, SV, ABPsys, ABPdiast, MAP) showed a large bias and wide limits of agreement. Percentage error was above 30% for all parameters except ABPsys.

CONCLUSION

The noninvasive device based on a modified Penaz technique cannot replace arterial blood pressure monitoring or TEE in anesthetized patients undergoing neurosurgery in sitting position.

Measurements of cardiac output obtained with transesophageal echocardiography and pulmonary artery thermodilution are not interchangeable

BACKGROUND

Echocardiography is increasingly becoming an integrated tool for circulatory evaluation in the intensive care unit and the operating room. Therefore, it is imperative to know the reproducibility of measurements obtained by echocardiography. In this study, a comparison of cardiac output (CO) measurements obtained with transesophageal echocardiography (TEE) and pulmonary artery catheter (PAC) thermodilution (TD) was carried out to test the precision, accuracy and trending ability of CO measurements obtained with TEE.

METHODS

Twenty-five patients completed the study. Each patient was placed in the following successive positions: supine, head-down tilt, head-up tilt, supine, supine with phenylephrine administration, pace heart rate 80 beats per minute (bpm), pace heart rate 110 bpm. TEE CO and PAC CO were measured simultaneously. The agreement was analysed by Bland-Altman plots, and to assess trending ability, a polar plot was constructed.

RESULTS

Both methods showed an acceptable precision 8% (PAC TD) and 16% (TEE). In comparison with PAC TD, the TEE was associated with a bias of -0.22 l/minute [95% confidence interval: -0.54; 0.10], wide limits of agreement (-1.73 l/minute; 1.29 l/minute), a percentage error of 38.6% and a trending ability with a radial degree of 53.6°, corresponding to a poor trending ability.

CONCLUSION

In comparison, CO measurements obtained with TEE and PAC TD had wide limits of agreement, a larger percentage error than would be expected from the precision of the two methods, and a poor trending ability. Thus, TEE is not interchangeable with PAC TD for measuring CO.

The role of transesophageal echocardiography in the intraoperative period

The goal of hemodynamic monitoring and management during major surgery is to guarantee adequate organ perfusion, a major prerequisite for adequate tissue oxygenation and thus, end-organ function. Further, hemodynamic monitoring should serve to prevent, detect, and to effectively guide treatment of potentially life-threatening hemodynamic events, such as severe hypovolemia due to hemorrhage, or cardiac failure. The ideal monitoring device does not exist, but some conditions must be met: it should be easy and operator-independently to use; it should provide adequate, reproducible information in real time. In this review we discuss in particular the role of intraoperative use of transesophageal echocardiography (TOE). Although TOE has gained special relevance in cardiac surgery, its role in major non cardiac surgery is still to be determined. We particularly focus on its ability to provide measurements of cardiac output (CO), and its role to guide fluid therapy. Within the last decade, concepts oriented on optimizing stroke volume and cardiac output mainly by fluid administration and guided by continuous monitoring of cardiac output or so called functional parameters of cardiac preload gained particular attention. Although they are potentially linked to an increased amount of fluid infusion, recent data give evidence that such pre-emptive concepts of hemodynamic optimization result in a decrease in morbidity and mortality. As TOE allows a real time direct visualization of cardiac structures, other potentially important advantages of its use also outside the cardiac surgery operation room can be postulated, namely the ability to evaluate the anatomical and functional integrity of the left and the right heart chambers. Finally, a practical approach to TOE monitoring is presented, based on a local experience.

Hemodynamic monitoring in sepsis

Arterial waveform analysis that does not require continuous calibration, impedance cardiography, electrical cardiometry, velocity-encoded phase contrast magnetic resonance imaging (MRI), pulsed dye densitometry, noninvasive pulse pressure analysis using tonometry, suprasternal Doppler, partial CO2 rebreathing techniques, and transcutaneous Doppler are just some of the other emerging technologies not described in this review that may be used routinely in the management of sepsis and septic shock in the very near future. These innovative approaches may further increase our ability to optimize patients' fluid status and hemodynamics. We also have ability to monitor the microcirculation. This increasingly sophisticated approach to the management of sepsis and septic shock will hopefully translate into better patient outcomes. However, optimal use of any hemodynamic monitoring requires an understanding of its physiologic underpinnings. Accurate interpretation of the hemodynamic information coupled with a protocolized management algorithm is the cornerstone of an effective resuscitation effort. Many forms of hemodynamic monitoring have emerged over the past 20 to 30 years with no convincing evidence for the superiority of any single techniques (Table 2). The goal of hemodynamic monitoring and optimization is to combat the systemic imbalance between tissue oxygen supply and demand ranging from global tissue hypoxia to overt shock and multiorgan failure. It remains unproven that hemodynamic monitoring of disease progression can effectively change patient outcome. However, despite our increased understanding of sepsis pathophysiology, mortality and morbidity from the disease remains high. Therefore, the search for the optimal parameters in resuscitation and the best way they can be monitored will continue.

Cardiac output monitoring: is there a gold standard and how do the newer technologies compare?

As a principal determinant of oxygen delivery and of blood pressure, cardiac output (CO) represents an important hemodynamic variable. Its accurate measurement, therefore, is important to the clinician caring for critically ill patients in a variety of care environments. Though the first clinical measurement of CO occurred 70 years ago, it was the introduction of the pulmonary artery catheter (PAC) with thermodilution-based determination of CO in the 1970s that set the stage for practical and widespread clinical measurement of CO. Although the usefulness and accuracy of this technique have justified its consideration as a "practical" gold standard in CO measurement, its drawbacks have driven the search for newer, less invasive measurement techniques. The last decade has seen the introduction of several such devices into the clinical arena. This article will serve to give a brief review of the history of CO measurement, to provide a discussion of the measurement of accuracy as it relates to CO measurement, and to discuss some of the newer methods and devices for CO measurement and how they have fared against a "practical" gold standard.

Hemodynamic monitoring in sepsis

Tissue hypoperfusion is an important factor in the development of multiple organ failure. Therefore, recognition of sepsis-induced tissue hypoperfusion and timely clinical intervention to prevent and correct this are fundamental aspects of managing patients with sepsis and septic shock. Hemodynamic monitoring plays a key role in the management of the critically ill and is used to identify hemodynamic instability and its cause and to monitor response to therapy. However, the utility of many forms of hemodynamic monitoring that are used in management of sepsis and septic shock remain controversial and unproven. This article examines emerging technologies as well as more established techniques used to monitor hemodynamics in sepsis and assesses their potential roles in optimization of sepsis-induced tissue hypoperfusion.

A novel operator-independent algorithm for cardiac output measurements based on three-dimensional transoesophageal colour Doppler echocardiography

AIMS

Cardiac output (CO) measurements from three-dimensional (3D) trans-mitral Doppler echocardiography are prone to error as manual selection of the region of interest (i.e. the site of measurement) is required. We newly developed an automated, user-independent algorithm to select the site of colour Doppler CO measurement. We aimed to validate this new method by benchmarking it against thermodilution, the current gold standard for CO measurements.

METHODS AND RESULTS

Transoesophageal colour 3D Doppler echocardiographic studies were obtained from 15 patients who also had received a pulmonary catheter for invasive CO measurements. Trans-mitral flow was determined using a novel operator-independent algorithm to automatically select the optimal site of measurement. The operator-independent CO measurements were referenced against thermodilution. A good correlation was found between operator-independent Doppler flow computations and thermodilution with a mean bias of 0.09 L/min, standard deviation of bias 1.3 L/min, and a 26% error (2 SD/mean CO). Mean CO was 4.94 L/min (range 3.10-7.10 L/min).

CONCLUSION

Our findings demonstrate that CO computation from transoesophageal colour 3D Doppler echo can be automated concerning the site of velocity measurement. Our operator-independent algorithm provides an objective and reproducible alternative to thermodilution.

What technique should I use to measure cardiac output?

PURPOSE OF REVIEW

Several less invasive cardiac output monitoring techniques are now commercially available and have the potential to replace the pulmonary artery catheter under certain clinical circumstances. The aim of this review is to give a synopsis of the currently available cardiac output measurement methods. This information should help in selecting the appropriate technique in a particular clinical setting.

RECENT FINDINGS

An overview is given of the currently available techniques for cardiac output monitoring. Recent validation studies demonstrate that pulse wave analysis may be used reliably as an alternative to the pulmonary artery catheter in different clinical settings. The use of transesophageal echocardiography and Doppler measurements is limited due to high operator dependency, the partial carbon dioxide rebreathing technique should be applied in a precisely defined clinical setting to mechanically ventilated patients only, and pulsed dye densitometry as well as the bioimpedance technique are currently primarily applied in an investigational setting.

SUMMARY

Less invasive cardiac output monitoring techniques may replace the pulmonary artery catheter in different clinical settings considering the specific properties of these techniques. The pulmonary artery catheter, however, may still be recommended for cardiac output measurement in specific clinical situations when monitoring of pulmonary artery pressures is desirable.

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.

Cardiac output measurements in off-pump coronary surgery: comparison between NICO and the Swan-Ganz catheter

BACKGROUND

The aim of this prospective study was to compare continuous cardiac output measurements of the non-invasive cardiac output system (NICO) with the pulmonary artery catheter during off-pump coronary bypass surgery.

METHODS

Twenty-two patients enrolled for off-pump coronary surgery received both a pulmonary artery catheter and a non-invasive cardiac output system for measurement of cardiac output. Data were compared by the Bland-Altman method to calculate the degree of agreement and to analyse if a significant difference existed between the two methods of cardiac output measurements.

RESULTS

Perioperatively, the non-invasive cardiac output underestimated cardiac output, but postoperatively overestimated it. The limits of agreement were larger during surgery compared to the postoperative period (-3.1; +2.5 vs. -1.4; +2.2 L min(-1)). Perioperatively, cardiac output measured with the pulmonary artery catheter varied from 0.5 to 7.5 L min(-1) (mean 3.6 L min(-1)) and with the non-invasive cardiac output from 0.5 to 8.4 L min(-1) (mean 3.9 L min(-1)). Postoperatively, these were 2.5-7.7 L min(-1) (mean 4.5 L min(-1)) and 2.3-8.4 L min(-1) (mean 4.9 L min(-1)), respectively.

CONCLUSION

During off-pump cardiac surgery, the non-invasive cardiac output reliably measures cardiac output and does it more rapidly than a pulmonary artery catheter and may be more useful in order to detect rapid haemodynamic changes.