Comparison of transesophageal echocardiographic, fick, and thermodilution cardiac output in critically ill patients

Transpulmonary thermodilution in patients treated with veno-venous extracorporeal membrane oxygenation

BACKGROUND

We tested the effect of different blood flow levels in the extracorporeal circuit on the measurements of cardiac stroke volume (SV), global end-diastolic volume index (GEDVI) and extravascular lung water index derived from transpulmonary thermodilution (TPTD) in 20 patients with severe acute respiratory distress syndrome (ARDS) treated with veno-venous extracorporeal membrane oxygenation (ECMO).

METHODS

Comparative SV measurements with transesophageal echocardiography and TPTD were performed at least 5 times during the treatment of the patients. The data were interpreted with a Bland-Altman analysis corrected for repeated measurements. The interchangeability between both measurement modalities was calculated and the effects of extracorporeal blood flow on SV measurements with TPTD was analysed with a linear mixed effect model. GEDVI and EVLWI measurements were performed immediately before the termination of the ECMO therapy at a blood flow of 6 l/min, 4 l/min and 2 l/min and after the disconnection of the circuit in 7 patients.

RESULTS

170 pairs of comparative SV measurements were analysed. Average difference between the two modalities (bias) was 0.28 ml with an upper level of agreement of 40 ml and a lower level of agreement of -39 ml within a 95% confidence interval and an overall interchangeability rate between TPTD and Echo of 64%. ECMO blood flow did not influence the mean bias between Echo and TPTD (0.03 ml per l/min of ECMO blood flow; p = 0.992; CI - 6.74 to 6.81). GEDVI measurement was not significantly influenced by the blood flow in the ECMO circuit, whereas EVLWI differed at a blood flow of 6 l/min compared to no ECMO flow (25.9 ± 10.1 vs. 11.0 ± 4.2 ml/kg, p = 0.0035).

CONCLUSIONS

Irrespectively of an established ECMO therapy, comparative SV measurements with Echo and TPTD are not interchangeable. Such caveats also apply to the interpretation of EVLWI, especially with a high blood flow in the extracorporeal circulation. In such situations, the clinician should rely on other methods of evaluation of the amount of lung oedema with the haemodynamic situation, vasopressor support and cumulative fluid balance in mind.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00021050). Registered 03/30/2020 https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017237.

Cardiac Output Measurement With Echocardiography and Pressure Recording Analytical Method in Pediatric Patients Admitted to the Cardiac Intensive Care Unit: A Retrospective Assessment of Bias Between the Two Methods

OBJECTIVES

This study aimed to compare, in a cohort of critically ill children with biventricular anatomy and no cardiovascular shunt, cardiac output (CO) and cardiac index (CI) assessed by echocardiography and a continuous pulse-contour method, MostCare^UP, to measure the differences between these techniques (biasCO and biasCI), and their association with clinical variables.

DESIGN

Retrospective study.

SETTING

Tertiary pediatric cardiac intensive care unit.

PARTICIPANTS

Children admitted to the pediatric cardiac intensive care unit who underwent echocardiography with CO measurement.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Thirty-five patients were included. BiasCO was -0.02 (0.26) L/min (percentage error 36%). BiasCI was 0.07 (0.34) L/min/m² (percentage error 18%). Biases and percentage errors were higher in 24 nonsupervised echocardiographies. A negative biasCO (overestimation by MostCare^UP) was associated with post-surgical status (v cardiomyopathy), higher systolic arterial pressure, and spontaneous breathing (v intubation). When only absolute values were considered, biasCO_NONEG correlated with age, weight, arterial pressure, and heart rate, whereas biasCI_NONEG was associated with a femoral arterial cannula, no use of inotropes, and the absence of mechanical ventilation. After adjustment, biasCO_NONEG remained independently associated with patients' body weight(p = 0.0001). BiasCI_NONEG showed a nonlinear relationship with weight below 20 kg and above 40 kg.

CONCLUSIONS

Children with extreme low or high weights, those who are extubated, and those with a femoral cannula carry the highest bias. When younger patients are considered, CI should be evaluated instead of CO, because biases are better highlighted by indexing data on body surface area. In children, both echocardiography and MostCare^UP may be responsible of inaccurate CO/CI assessment.

Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis

Echocardiography, as a noninvasive hemodynamic evaluation technique, is frequently used in critically ill patients. Different opinions exist regarding whether it can be interchanged with traditional invasive means, such as the pulmonary artery catheter thermodilution (TD) technique. This systematic review aimed to analyze the consistency and interchangeability of cardiac output measurements by ultrasound (US) and TD. Five electronic databases were searched for studies including clinical trials conducted up to June 2019 in which patients’ cardiac output was measured by ultrasound techniques (echocardiography) and TD. The methodological quality of the included studies was evaluated by two independent reviewers who used the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2), which was tailored according to our systematic review in Review Manager 5.3. A total of 68 studies with 1996 patients were identified as eligible. Meta-analysis and subgroup analysis were used to compare the cardiac output (CO) measured using the different types of echocardiography and different sites of Doppler use with TD. No significant differences were found between US and TD (random effects model: mean difference [MD], -0.14; 95% confidence interval, -0.30 to 0.02; P = 0.08). No significant differences were observed in the subgroup analyses using different types of echocardiography and different sites except for ascending aorta (AA) (random effects model: mean difference [MD], -0.37; 95% confidence interval, -0.74 to -0.01; P = 0.05) of Doppler use. The median of bias and limits of agreement were -0.12 and ±0.94 L/min, respectively; the median of correlation coefficient was 0.827 (range, 0.140–0.998). Although the difference in CO between echocardiography by different types or sites and TD was not entirely consistent, the overall effect of meta-analysis showed that no significant differences were observed between US and TD. The techniques may be interchangeable under certain conditions.

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.

Perioperative transesophageal echocardiography for non-cardiac surgery

PURPOSE

The use of transesophageal echocardiography (TEE) has evolved to include patients undergoing high-risk non-cardiac procedures and patients with significant cardiac disease undergoing non-cardiac surgery. Implementation of basic TEE education in training programs has increased across a broad spectrum of procedures in the perioperative arena. This paper describes the use of perioperative TEE in non-cardiac surgery and provides an overview of the basic TEE examination.

PRINCIPAL FINDINGS

Perioperative TEE is used to monitor hemodynamic parameters in non-cardiac procedures where there is a high risk of hemodynamic instability. Its use extends to include moderate-risk procedures for patients with significant cardiac diseases such as low ejection fraction, hypertrophic cardiomyopathy, severe valve lesions, or congenital heart disease. Vascular procedures involving the aorta, blunt trauma, and liver transplantation are all examples of procedures that may benefit from TEE. Transesophageal echocardiography examination allows assessment of volume status, ventricular function, diagnosis of gross valvular pathology and pericardial tamponade, as well as close monitoring of cardiac output, response to therapy, and the impact of ongoing surgical manipulation. In patients with unexplained and unexpected hemodynamic instability, "rescue TEE" can be used to help identify the underlying cause.

CONCLUSIONS

Perioperative TEE is emerging as a preferred tool to manage hemodynamics in high-risk procedures and in high-risk patients undergoing non-cardiac surgery. A rescue TEE examination protocol is a helpful approach for early identification of the etiology of hemodynamic instability.

Validation study of the accuracy of echocardiographic measurements of systemic blood flow volume in newborn infants

BACKGROUND

The echocardiographic assessment of circulatory function in sick newborn infants has the potential to improve patient care. However, measurements are prone to error and have not been sufficiently validated. Phase-contrast magnetic resonance imaging (MRI) provides highly validated measures of blood flow and has recently been applied to the newborn population. The aim of this study was to validate measures of left ventricular output and superior vena caval flow volume in newborn infants.

METHODS

Echocardiographic and MRI assessments were performed within 1 working day of each other in a cohort of newborn infants.

RESULTS

Examinations were performed in 49 infants with a median corrected gestational age at scan of 34.43 weeks (range, 27.43-40 weeks) and a median weight at scan of 1,880 g (range, 660-3,760 g). Echocardiographic assessment of left ventricular output showed a strong correlation with MRI assessment (R(2) = 0.83; mean bias, -9.6 mL/kg/min; limits of agreement, -79.6 to +60.0 mL/kg/min; repeatability index, 28.2%). Echocardiographic assessment of superior vena caval flow showed a poor correlation with MRI assessment (R(2) = 0.22; mean bias, -13.7 mL/kg/min; limits of agreement, -89.1 to +61.7 mL/kg/min; repeatability index, 68.0%). Calculating superior vena caval flow volume from an axial area measurement and applying a 50% reduction to stroke distance to compensate for overestimation gave a slightly improved correlation with MRI (R(2) = 0.29; mean bias, 2.6 mL/kg/min; limits of agreement, -53.4 to +58.6 mL/kg/min; repeatability index, 54.5%).

CONCLUSIONS

Echocardiographic assessment of left ventricular output appears relatively robust in newborn infant. Echocardiographic assessment of superior vena caval flow is of limited accuracy in this population, casting doubt on the utility of the measurement for diagnostic decision making.

Validation of a new method based on ultrasound velocity dilution to measure cardiac output in paediatric patients

PURPOSE

To validate a novel method of ultrasound dilution (COstatus(®); Transonic Systems, Ithaca, NY) for measuring cardiac output in paediatric patients after biventricular repair of congenital heart disease.

METHODS

Children undergoing biventricular repair of congenital heart disease were prospectively identified. Patients with significant intracardiac shunts were excluded. Postoperative cardiac output was measured by ultrasound dilution (COud) and concurrently calculated by the Fick equation (COrms) using measured oxygen consumption by respiratory mass spectrometry.

RESULTS

Thirty-five patients were studied generating 66 individual data sets. Subjects had a median (interquartile range) age of 147 days (11, 216), weight of 4.98 kg (3.78, 6.90) and body surface area of 0.28 m(2) (0.22, 0.34). Of the patients, 66% had peripheral arterial catheters and 34% had femoral cannulation; peripheral arterial lines accounted for 6/8 of unsuccessful studies due to inability to generate sufficient flow. The site of the central venous cannula did not impact the feasibility of completing the study. A mean bias of 0.00 L/min [2 standard deviation (SD) ± 0.76 L/min] between COud and COrms was found with a percentage error of 97%. When comparing cardiac index, bias increased to 0.13 L/min/m(2) (2SD ± 2.16 L/min/m(2)).

CONCLUSIONS

Cardiac output by ultrasound dilution showed low bias with wide limits of agreement when compared to measurement derived by the Fick equation. Although measurements through central and peripheral arterial lines were completed with minimal difficulties in the majority of patients, the application of COstatus(®) in neonates with low body surface area may be limited.

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.

Planimetry of the aortic valve orifice area: comparison of multislice spiral computed tomography and magnetic resonance imaging

OBJECTIVE

We sought to determine the comparability of multislice computed tomography (MSCT) and magnetic resonance imaging (MRI) for measuring the aortic valve orifice area (AVA) and grading aortic valve stenosis.

MATERIALS AND METHODS

Twenty-seven individuals, among them 18 patients with valvular stenosis, underwent AVA planimetry by both MSCT and MRI. In the subset of patients with valvular stenosis, AVA was also calculated from transthoracic Doppler echocardiography (TTE) using the continuity equation.

RESULTS

There was excellent correlation between MSCT and MRI (r = 0.99) and limits of agreement were in an acceptable range (± 0.42 cm(2)) although MSCT yielded a slightly smaller mean AVA than MRI (1.57 ± 0.83 cm(2) vs. 1.67 ± 0.98 cm(2), p < 0.05). However, in the subset of patients with valvular stenosis, the mean AVA was not different between MSCT and MRI (1.05 ± 0.30 cm(2) vs. 1.04 ± 0.39 cm(2); p > 0.05). The mean AVAs on both MSCT and MRI were systematically larger than on TTE (0.88 ± 0.28 cm(2), p < 0.001 each). Using an AVA of 1.0 cm(2) on TTE as reference, the best threshold for detecting severe-to-critical stenosis on MSCT and MRI was an AVA of 1.25 cm(2) and 1.30 cm(2), respectively, resulting in an accuracy of 96% each.

CONCLUSION

Our study specifies recent reports on the suitability of MSCT for quantifying AVA. The data presented here suggest that certain methodical discrepancies of AVA measurements exist between MSCT, MRI and TTE. However, MSCT and MRI have shown excellent correlation in AVA planimetry and similar accuracy in grading aortic valve stenosis.

Planimetry of Aortic Valve Area in Aortic Stenosis by Magnetic Resonance Imaging

BACKGROUND

The aim of the study was to determine whether noninvasive planimetry of aortic valve area (AVA) by magnetic resonance imaging (MRI) is feasible and reliable in patients with valvular aortic stenosis in comparison to transesophageal echocardiography (TEE) and catheterization.

METHODS AND RESULTS

Planimetry of AVA by MRI (MRI-AVA) was performed on a clinical magnetic resonance system (1.5-T Sonata, Siemens Medical Solutions) in 33 patients and compared with AVA calculated invasively by the Gorlin-formula at catheterization (CATH-AVA, n = 33) as well as to AVA planimetry by multiplane TEE (TEE-AVA, n = 27). Determination of MRI-AVA was possible with an adequate image quality in 82% (27/33), whereas image quality of TEE-AVA was adequate only in 56% (15/27) of patients because of calcification artifacts (P = 0.05). The correlation between MRI-AVA and CATH-AVA was 0.80 (P < 0.0001) and the correlation of MRI-AVA and TEE-AVA was 0.86 (P < 0.0001). MRI-AVA overestimated TEE-AVA by 15% (0.98 +/- 0.31 cm2 vs. 0.85 +/- 0.3 cm2, P < 0.001) and CATH-AVA by 27% (0.94 +/- 0.29 cm2 vs. 0.74 +/- 0.24 cm2, P < 0.0001). Nevertheless, a MRI-AVA below 1,3 cm2 indicated severe aortic stenosis (CATH-AVA < 1 cm2) with a sensitivity of 96% and a specificity of 100% (ROC area 0.98).

CONCLUSIONS

Planimetry of aortic valve area by MRI can be performed with better image quality as compared with TEE. In the clinical management of patients with aortic stenosis, it has to be considered that MRI slightly overestimates aortic valve area as compared with catheterization despite an excellent correlation.

Stroke volume equation for impedance cardiography

The study's goal was to determine if cardiac output (CO), obtained by impedance cardiography (ICG), would be improved by a new equation N, implementing a square root transformation for dZ/dtmax/Z0, and a variable magnitude, mass-based volume conductor Vc. Pulmonary artery catheterisation was performed on 106 cardiac surgery patients pre-operatively. Post-operatively, thermodilution cardiac output (TDCO) was simultaneously compared with ICG CO. dZ/dtmax/Z0 and Z0 were obtained from a proprietary bioimpedance device. The impedance variables, in addition to left ventricular ejection time TLVE and patient height and weight, were input using four stroke volume (SV) equations: Kubicek (K), Sramek (S), Sramek-Bernstein (SB), and a new equation N. CO was calculated as SV x heart rate. Data are presented as mean +/- SD. One way repeated measures of ANOVA followed by the Tukey test were used for inter-group comparisons. Bland-Altman methods were used to assess bias, precision and limits of agreement. P< 0.05 was considered statistically significant. CO implementing N (6.06 +/- 1.48 l min(-1)) was not different from TDCO (5.97 +/- 1.41 l min(-1)). By contrast, CO calculated using K (3.70 +/- 1.53 l min(-1)), S (4.16 +/- 1.83 l min(-1)) and SB (4.37 +/- 1.82 l min(-1)) was significantly less than TDCO. Bland-Altman analysis showed poor agreement between TDCO and K, S and SB, but not between TDCO and N. Compared with TDCO, equation N, using a square-root transformation for dZ/dtmax/Z0, and a mass-based Vc, was superior to existing transthoracic impedance techniques for SV and CO determination.

Planimetry of mitral valve stenosis by magnetic resonance imaging

OBJECTIVES

We sought to determine whether noninvasive planimetry of the mitral valve area (MVA) by magnetic resonance imaging (MRI) is feasible and reliable in patients with mitral stenosis (MS).

BACKGROUND

Accurate assessment of MVA is particularly important for the management of patients with valvular stenosis. Current standard techniques for assessing the severity of MS include echocardiography (ECHO) and cardiac catheterization (CATH).

METHODS

In 22 patients with suspected or known MS, planimetry of MVA was performed with a 1.5-T magnetic resonance scanner using a breath-hold balanced gradient echo sequence (true FISP). Data were compared with echocardiographically determined MVA (ECHO-MVA, n = 22), as well as with invasively calculated MVA by the Gorlin-formula at (CATH-MVA, n = 17).

RESULTS

The correlation between MRI- and CATH-MVA was 0.89 (p < 0.0001), and the correlation between MRI- and ECHO-MVA was 0.81 (p < 0.0001). The MRI-MVA slightly overestimated CATH-MVA by 5.0% (1.60 +/- 0.45 cm(2) vs. 1.52 +/- 0.49 cm(2), p = NS) and ECHO-MVA by 8.1% (1.61 +/- 0.42 cm(2) vs. 1.48 +/- 0.42 cm(2), p < 0.05). On receiver-operating characteristic curve analysis, a value of MRI-MVA below 1.65 cm(2) indicated mitral stenosis (CATH-MVA < or =1.5 cm(2)), with a good sensitivity and specificity (89% and 75%, respectively).

CONCLUSIONS

Magnetic resonance planimetry of the mitral valve orifice in mitral stenosis offers a reliable and safe method for noninvasive quantification of mitral stenosis. In the clinical management of patients with mitral stenosis, it has to be considered that planimetry by MRI slightly overestimates MVA, as compared with MVA calculated echocardiographically and at catheterization.

Comparison of Cardiac Output Determined by Bioimpedance, Thermodilution, and the Fick Method

• Background Cardiac output can be determined by using a variety of methods.

• Objectives To determine the precision and bias between 3 methods for determining cardiac output: bioimpedance, thermodilution, and the Fick method.

• Methods Cardiac output was determined by using bioimpedance via neck and thorax patches and thermodilution via pulmonary artery catheter in 46 patients in the intensive care unit. A subset of 15 patients also had cardiac output determined by using the Fick method.

• Results Mean (SD) cardiac output in all patients was 6.3 (2.2) L/min by thermodilution and 5.6 (2.0) L/min by bioimpedance. In the 15 patients in whom all 3 methods were used, mean cardiac output was 6.0 (1.7) L/min by thermodilution, 5.3 (1.7) L/min by bioimpedance, and 8.6 (4.5) L/min by the Fick method. Bias and precision (mean difference ± 2 SDs) were 0.7 ± 2.9 L/min between thermodilution and bioimpedance, 1.7 ± 3.8 L/min between the Fick method and thermodilution, and 2.4 ± 4.7 L/min between the Fick method and bioimpedance.

• Conclusion Bioimpedance, thermodilution, and Fick determinations of cardiac outputs are not interchangeable in a heterogenous population of critically ill patients.

Measurement of cardiac output before and after cardiopulmonary bypass: Comparison among aortic transit-time ultrasound, thermodilution, and noninvasive partial CO2 rebreathing

OBJECTIVES

A noninvasive continuous cardiac output system (NICO) has been developed recently. NICO uses a ratio of the change in the end-tidal carbon dioxide partial pressure and carbon dioxide elimination in response to a brief period of partial rebreathing to measure CO. The aim of this study was to compare the agreement among NICO, bolus (TDCO), and continuous thermodilution (CCO), with transit-time flowmetry of the ascending aorta using an ultrasonic flow probe (UFP) before and after cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational human study.

SETTING

Veterans Affairs Medical Center Hospital.

PARTICIPANTS

Sixty-eight patients.

METHODS

Matched sets of CO measurements between NICO, TDCO, CCO, and UFP were collected in 68 patients undergoing elective CABG at specific time periods before and after separation from CPB. After anesthetic induction, all patients had an NICO sensor attached between the endotracheal tube and the breathing circuit, a PAC floated into the pulmonary artery for TDCO and CCO monitoring, and a UFP positioned on the ascending aorta and used for the reference CO. Bland-Altman analysis was used to compare the agreement among the different methods.

MEASUREMENTS AND MAIN RESULTS

Bland-Altman analysis of CO measurements before CPB yielded a bias, precision, and percent error of 0.04 L/min +/- 1.07 L/min (44.8%) for NICO, 0.18 L/min +/- 1.01 L/min (41.7%) for TDCO, and 0.29 L/min +/- 1.40 L/min (57.5%) for CCO compared with simultaneous UFP CO measurements, respectively. After separation from CPB (average 29 mins), bias, precision, and percent error were -0.46 L/min +/- 1.06 L/min (37.3%) for NICO, 0.35 L/min +/- 1.39 L/min (46.1%) for TDCO, and 0.36 L/min +/- 1.96 L/min (64.7%) for CCO compared with UFP CO measurements, respectively.

CONCLUSIONS

Before initiation of CPB, the accuracy for all 3 techniques was similar. After separation from CPB, the tendency was for NICO to underestimate CO and for TDCO and CCO to overestimate it. NICO offers an alternative to invasive CO measurement.

Cardiac output measurement after coronary artery bypass grafting using bolus thermodilution, continuous thermodilution, and whole-body impedance cardiography

OBJECTIVE

To test the feasibility of continuous cardiac output (CO) monitoring with whole-body impedance cardiography after coronary artery bypass grafting and to compare the values obtained with those measured using the bolus and continuous thermodilution methods.

DESIGN

A prospective study.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Twenty patients after coronary artery bypass grafting.

INTERVENTIONS

CO was measured intermittently using the bolus thermodilution method, and continuously using the continuous thermodilution method, and whole-body impedance cardiography immediately after transfer to the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

Bolus thermodilution CO was measured in triplicate at up to 14 time points overnight. Continuous thermodilution CO and whole-body impedance cardiography CO values were recorded simultaneously. During the study period, the bias in CO values between bolus thermodilution and whole-body impedance cardiography ranged from 0.07 to 1.05 L/min and the precision (standard deviation of differences) ranged from 0.82 to 1.31 L/min. The bias between the bolus and continuous thermodilution methods ranged from 0.06 to 0.58 L/min and the precision from 0.43 to 1.02 L/min. Pulmonary artery temperature and CO level were the major determinants of the bias and precision in both comparisons.

CONCLUSIONS

Agreement between whole-body impedance cardiography and bolus thermodilution is slightly inferior to that between the bolus and continuous thermodilution methods but not to the extent that it hampers the use of whole-body impedance cardiography for the continuous monitoring of CO after coronary artery bypass surgery.

Comparison of cardiac output measured with echocardiographic volumes and aortic Doppler methods during mechanical ventilation

OBJECTIVE

To compare two transesophageal echocardiographic methods of cardiac output and stroke volume measurement in mechanically ventilated patients.

DESIGN

Prospective clinical study.

SETTING

Operating room (group I) and intensive care unit (group II) in two university hospitals.

PATIENTS

Fifteen deeply anesthetized patients undergoing gynecological laparoscopy for sterility (group I) and 40 patients with septic shock (group II).

INTERVENTIONS

Transesophageal echocardiography with modification of hemodynamic conditions.

MEASUREMENTS AND RESULTS

Left ventricular (LV) volumes, cardiac (CI) and stroke index (SI) were measured with two methods using either LV volumes or aortic Doppler. These values were significantly lower in group I compared to group II. Using ANOVA and paired t-tests, there were no significant differences between the two methods of measurement. Correlation between these methods was better in group II than in group I, although not significantly so. In group I, bias for CI measurements was low (0.05 l/min per m(2)), with a weak agreement in terms of the 95% confidence interval (-1.17; 1.06 l/min per m(2)) compared to the mean values obtained with both methods (1.3 l/min per m(2)). In group II, bias for CI measurements was lower (0.2 l/min per m(2)). Agreement was weak, regarding 95% confidence intervals (-1.7; 1.3 l/min per m(2)) compared to the mean values (3 l/min per m(2) with the LV volumes method and 3.2 l/min per m(2) and with the Doppler method).

CONCLUSIONS

Cardiac output and stroke volume can be measured from LV volumes in mechanically ventilated patients, yielding relevant information. However, the accuracy of LV volume measurements is not excellent compared to the aortic Doppler method. Thus, this latter technique should still be considered as the gold standard.

Comparison of bedside measurement of cardiac output with the thermodilution method and the Fick method in mechanically ventilated patients

INTRODUCTION

Bedside cardiac output determination is a common preoccupation in the critically ill. All available methods have drawbacks. We wished to re-examine the agreement between cardiac output determined using the thermodilution method (QTTHERM) and cardiac output determined using the metabolic (Fick) method (QTFICK) in patients with extremely severe states, all the more so in the context of changing practices in the management of patients. Indeed, the interchangeability of the methods is a clinically relevant question; for instance, in view of the debate about the risk-benefit balance of right heart catheterization.

PATIENTS AND METHODS

Eighteen mechanically ventilated passive patients with a right heart catheter in place were studied (six women, 12 men; age, 39-84 years; simplified acute physiology scoreII, 39-111). QTTHERM was obtained using a standard procedure. QTFICK was measured from oxygen consumption, carbon dioxide production, and arterial and mixed venous oxygen contents. Forty-nine steady-state pairs of measurements were performed. The data were normalized for repeated measurements, and were tested for correlation and agreement.

RESULTS

The QTFICK value was 5.2 +/- 2.0 l/min whereas that of QTTHERM was 5.8 +/- 1.9 l/min (R = 0.840, P < 0.0001; mean difference, -0.7 l/min; lower limit of agreement, -2.8 l/min; upper limit of agreement, 1.5 l/min). The agreement was excellent between the two techniques at QTTHERM values <5 l/min but became too loose for clinical interchangeability above this value. Tricuspid regurgitation did not influence the results.

DISCUSSION AND CONCLUSIONS

No gold standard is established to measure cardiac output in critically ill patients. The thermodilution method has known limitations that can lead to inaccuracies. The metabolic method also has potential pitfalls in this context, particularly if there is increased oxygen consumption within the lungs. The concordance between the two methods for low cardiac output values suggests that they can both be relied upon for clinical decision making in this context. Conversely, a high cardiac output value is more difficult to rely on in absolute terms.

Quantification of valvular aortic stenosis by magnetic resonance imaging

BACKGROUND

Assessing the aortic valvular orifice is important in judging the severity of aortic stenosis. Magnetic resonance imaging visualizes in-plane valvular motion. We studied the value of magnetic resonance planimetry of the aortic valve orifice.

METHODS

We used breath-hold gradient echocardiographic sequences on a clinical magnetic resonance system (1.5 T) and studied 25 patients with symptomatic valvular aortic stenosis. We performed a planimetry of the valvular orifice in systolic images of the valvular plane. The results were compared with echocardiography (continuity equation) and cardiac catheterization (Gorlin formula).

RESULTS

Magnetic resonance planimetry was feasible in all patients, and the image quality was invariably adequate. The magnetic resonance imaging results correlated well with the data calculated from catheterization and less robustly with the echocardiographic results. The 3 methods were similar in terms of leading to clinical decisions.

CONCLUSIONS

We suggest that magnetic resonance flow planimetry of the aortic valve orifice offers a simple, reliable, fast, and safe method to noninvasively quantify aortic stenosis.

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.

Haemodynamic changes and vasopressin release are not consistently associated with carbon dioxide pneumoperitoneum in humans

BACKGROUND

Conflicting haemodynamic changes, suggested to be caused by vasopressin release, have been reported during carbon dioxide (CO2) pneumoperitoneum. However, peritoneal stimulations including open surgery cause both a systemic vasopressor response and a vasopressin release, which are suppressed by opiate administration. Also, a decreased venous return of blood to the heart causes vasopressin release. Furthermore, previous haemodynamic assessments of laparoscopic surgery have been conducted using various anaesthetic regimens, which are likely to have caused various haemodynamic effects. We hypothesised that intraoperative haemodynamic and/or humoral changes would not be observed in association with laparoscopic surgery provided that, (a) normovolaemia is continuously maintained using transoesophageal echocardiographic (TEE) assessment, and (b) adequate depth of general anaesthesia is continuously maintained by bispectral index (BIS) monitoring and high plasma Ievel opiate administration.

METHODS

Twenty ASA 1 women undergoing laparoscopic surgery received 10 ml. kg-1 lactated Ringer's solution and thereafter were randomly allocated to receive intraoperatively either 8 ng. ml-1 or 4 ng. ml-1 plasma remifentanil concentrations while BIS was maintained at 50+/-5 by isoflurane alteration. The group receiving 4 ng. ml-1 remifentanil was used as control. Expired CO2 was maintained within a 32-38 kPa range throughout the investigation. Complete TEE haemodynamic investigation was performed before pneumoperitoneum (PP) (T1), and during PP horizontal (T2), with a head-up tilt (T3), with a head-down tilt (T4), horizontal (T5), and PP released (T6). Plasma vasopressin, epinephrine and norepinephrine levels were measured at T1, T3, and T6. ANOVA, Student's t-test and Mann-Whitney U-test were used for statistical analysis.

RESULTS

Haemodynamic indices and humoral values did not change significantly within and between remifentanil groups throughout the investigation (all P<0.05).

CONCLUSION

Continuous adequate depth of anaesthesia and normovolaemia may have prevented both a humoral and a haemodynamic response, initiated in the peritoneum by the contact with CO2 in previous investigations.

Transesophageal echocardiography (TEE) in the critical care patient

Critically ill patients often pose special diagnostic problems to the clinician, intensified by limited physical examination findings and difficulty in transportation to imaging suites. Mechanical ventilation and the limited ability to position the patient make transthoracic echocardiography difficult. Transesophageal echocardiographic (TEE) imaging, however, is well suited to the critical care patient and is frequently used to evaluate hemodynamic status, the presence of vegetations, a cardioembolic source, and an intracardiac cause of hypoxemia. Using proper precautions, TEE can be performed safely in unstable patients and frequently leads to important changes in management.

Pediatric cardiac output measurement using surface integration of velocity vectors: an in vivo validation study

OBJECTIVE

To test the accuracy and reproducibility of systemic cardiac output (CO) measurements using surface integration of velocity vectors (SIVV) in a pediatric animal model with hemodynamic instability and to compare SIVV with traditional pulsed-wave Doppler measurements.

DESIGN

Prospective, comparative study.

SETTING

Animal research laboratory at a university medical center.

SUBJECTS

Eight piglets weighing 10-15 kg.

INTERVENTIONS

Hemodynamic instability was induced by using inhalation of isoflurane and infusions of colloid and dobutamine.

MEASUREMENTS

SIVV CO was measured at the left ventricular outflow tract, the aortic valve, and ascending aorta. Transit time CO was used as the reference standard.

RESULTS

There was good agreement between SIVV and transit time CO. At high frame rates, the mean difference +/- 2 SD between the two methods was 0.01+/-0.27 L/min for measurements at the left ventricular outflow tract, 0.08+/-0.26 L/min for the ascending aorta, and 0.06+/-0.25 L/min for the aortic valve. At low frame rates, measurements were 0.06+/-0.25, 0.19+/-0.32, and 0.14+/-0.30 L/min for the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. There were no differences between the three sites at high frame rates. Agreement between pulsed-wave Doppler and transit time CO was poorer, with a mean difference +/- 2 SD of 0.09+/-0.93 L/min. Repeated SIVV measurements taken at a period of relative hemodynamic stability differed by a mean difference +/-2 SD of 0.01+/-0.22 L/min, with a coefficient of variation = 7.6%. Intraobserver coefficients of variation were 5.7%, 4.9%, and 4.1% at the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. Interobserver variability was also small, with a coefficient of variation = 8.5%.

CONCLUSIONS

SIVV is an accurate and reproducible flow measurement technique. It is a considerable improvement over currently used methods and is applicable to pediatric critical care.

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

This study assessed the agreement between three methods of cardiac output (CO) measurement, thermodilution, the current clinical standard, and two transoesophageal echocardiographic techniques. Measurements were performed in 37 patients using thermodilution, continuous wave Doppler across the aortic valve and pulsed wave Doppler positioned in the left ventricular outflow tract. The aortic valve area was measured by direct planimetry, and the left ventricular outflow tract area was calculated from its diameter. Weighted least products regression analysis was employed to detect bias, and standard deviation of the difference (SDdiff) was calculated. There was no fixed bias but there was proportional bias between continuous wave Doppler and thermodilution methods (SDdiff 0.92 l/min). There was fixed bias but not proportional bias between pulsed wave and thermodilution methods (SDdiff 1.1 l/min). There was neither fixed nor proportional bias between pulsed wave and continuous wave Doppler methods (SDdiff 1.1 l/min). The transoesophageal Doppler methods described can be clinical alternatives to thermodilution cardiac output measurement.

Cardiac output can be reliably measured noninvasively after coronary artery bypass grafting operation

OBJECTIVE

To evaluate the reliability of whole-body impedance cardiography in the measurement of cardiac output after coronary artery bypass grafting operation in comparison with the thermodilution method.

DESIGN

Prospective, consecutive sampling.

PATIENTS

A total of 82 patients undergoing coronary artery bypass surgery were investigated. In a group of 41 patients who were intubated, cardiac output measurements were taken simultaneously with whole-body impedance cardiography and the thermodilution method within the first 3 hrs after the operation (early intensive care unit [ICU] period). In another group of 41 patients, the measurements were taken before the operation and in the second 12 hrs after cardiac surgery (late ICU period).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The agreement between the thermodilution and whole-body impedance cardiography cardiac output measurements was good before the operation, bias 0.04 +/- 1.64 L/min (n = 41), and in the late ICU period, bias 0.00 +/- 1.84 L/min (+/-2 SD) (n = 41). The results were within 20% in 81%-85% of the cases. The agreement was satisfactory in the early ICU period, bias 0.38 +/- 2.74 L/min (n = 41). It was presumed that thermal instability of the patients was one possible source of measurement errors in the thermodilution method, causing reduced agreement between the methods in this period. The repeatability values (rv = 2.83 x SDs) for whole-body impedance cardiography were 0.44 L/min before the operation, 0.30 L/min in the early ICU period, and 0.65 L/min in the late ICU period, being significantly better than for the thermodilution method (0.79, 0.51, and 1.11 L/min, respectively) in all phases of the investigation (p < .001). The agreement between the thermodilution method and whole-body impedance cardiography is similar to reported comparisons between invasive methods in analogous settings.

CONCLUSIONS

Whole-body impedance cardiography reliably measures cardiac output in patients after coronary artery bypass grafting operation. The excellent repeatability of whole-body impedance cardiography enhances the value of the method in continuous monitoring of patients after the operation.

Non-invasive cardiac output determination: state of the art

This review deals with recent developments in non-invasive cardiac output measurement. In the past few years significant progress has been made with semi-invasive transoesophageal echocardiography; the method now provides advanced facilities to measure cardiac output and other important characteristics of cardiac function. The method is, however, operator-dependent and the equipment used is expensive, which means that large-scale use on intensive care patients is not feasible. Whole-body impedance cardiography has recently shown good accuracy and flexibility in use, and seems to be the most promising method for the non-invasive measurement of cardiac output.

Continuous noninvasive measurement of aortic blood flow in critically ill patients with a new esophageal echo-Doppler system

PURPOSE

Determination of aortic blood flow (ABF) using esophageal Doppler has been proposed as a low invasive hemodynamic monitoring method. The esophageal echo-Doppler Dynemo 3000 (Sometec Inc., Paris, France) system, recently available on the market, is an original device measuring simultaneously, and at the same anatomic level, aortic diameter, and blood flow velocity. Until now, this material has been used exclusively for peroperative monitoring. The objectives of the study were to assess the feasibility and reliability of use for continuous measurements of ABF in hemodynamically compromised intensive care unit patients; and to compare ABF values and its change induced by preload manipulation with the cardiac output (CO) values measured simultaneously by the standard thermodilution method.

MATERIALS AND METHODS

Sixty simultaneous measurements of ABF and CO were performed in 22 intensive care unit patients. In 16 hypovolemic patients, Doppler and thermodilution measurements were repeated after fluid replacement.

RESULTS

Applicability of the method was 84.6% (failure of the echo-Doppler method in 4 of 26 eligible patients). Coefficient of variation of echo-Doppler-derived ABF was 3.25 +/- 2.26%. Interobserver variability was 3.3 +/- 1.6%. Close linear relationship was found between ABF and CO (r = 0.92). Average ABF/CO ratio was 73 +/- 10%, but significant variation was observed after fluid replacement.

CONCLUSIONS

The echo-Doppler Dynemo 3000 system allows reliable continuous measurements of ABF in intensive care unit patients, both easily and safely.

Non-invasive measurement of cardiac output: whole-body impedance cardiography in simultaneous comparison with thermodilution and direct oxygen Fick methods

OBJECTIVE

To determine the reliability of whole-body impedance cardiography (ICGWB), with electrodes attached to wrists and ankles, in the measurement of cardiac output (CO) on the basis of simultaneous comparison with thermodilution (TD) and direct oxygen Fick (Fick) methods.

DESIGN

Prospective clinical study.

SETTING

A surgical intensive care unit at a university hospital.

PATIENTS

Thirty consecutive subjects undergoing a coronary artery bypass surgery were investigated preoperatively.

MEASUREMENTS

ICGWB derived CO was measured simultaneously with the TD and Fick methods to establish the biases and limits of agreement (LA) between the methods.

RESULTS

The results obtained by ICGWB and the invasive methods showed good agreement. The bias and LA between COTD and COICG were 0.00 l/min: 1.37 and 1.37 l/min, respectively, and were close to those obtained between COTD and COFICK, 0.32 l/min; 1.74 and -1.10 l/min. The bias and LA between the COFICK and COICG were -0.32 l/min; -2.24 and 1.60 l/min respectively. The repeatability value of consecutive single measurements for ICGWB (RVICG = 0.57 l/min) was much better than for the TD method (RVTD = 1.10 l/min).

CONCLUSION

There was close agreement between the results of the three methods in the measurement of CO. In sedated preoperative patients the accuracy of ICGWB is within clinically acceptable limits and its repeatability is excellent. ICGWB provides a useful alternative to the TD and Fick methods in cases where the pressures supplied by the pulmonary artery catheter are not essential.

Small hemodynamic effect of typical rapid volume infusions in critically ill patients

OBJECTIVES

To determine what volumes are commonly used for rapid volume infusions in critically ill patients admitted to the intensive care unit (ICU) for > 12 hrs; and to determine the effectiveness of a typical rapid volume infusion in producing hemodynamic change and increasing left ventricular end-diastolic volume.

DESIGN

A prospective survey of clinical practice (part 1) and a prospective clinical investigation (part 2).

SETTING

Two hospital ICUs (11 and six beds) of which one is university affiliated.

PATIENTS

Critically ill patients admitted to the ICU for > 12 hrs.

INTERVENTIONS

Infusion of 500 mL of normal saline over 5 to 10 mins.

MEASUREMENTS AND MAIN RESULTS

For 1 month, we recorded the volume and composition of all volume infusions given as a rapid bolus in patients admitted to the ICU for > 12 hrs. We then measured the effected the median rapid volume infusion in a subset of 13 patients by measuring hemodynamics (using arterial and pulmonary artery flotation catheters) and left ventricular end-diastolic area (using transgastric short-axis views from transesophageal echocardiograms). During 470 patient days, 159 rapid volume infusions were administered. The average rapid volume infusion administered was 390 +/- 160 mL (median 500; interquartile range 250 to 500). Crystalloid solutions were used for two thirds of the rapid volume infusions and colloid solutions were used for one third of the rapid volume infusions. The rapid volume infusion of 500 mL of saline did not significantly increase mean arterial pressure (78.0 +/- 11.9 to 79.3 +/- 14.6 mm Hg), cardiac index (4.3 +/- 1.7 to 4.6 +/- 1.8 L/min/m2), right atrial pressure (11.1 +/- 3.8 to 12.4 +/- 3.3 mm Hg), left ventricular end-diastolic area (8.6 +/- 1.7 to 9.1 +/- 1.8 cm2/m2), or left ventricular end-systolic area (3.5 +/- 1.5 to 3.6 +/- 1.5 cm2/m2). Pulmonary artery occlusion pressure increased slightly but significantly from 12.9 +/- 3.4 to 14.7 +/- 3.3 mm Hg (p < .05).

CONCLUSIONS

After patients are admitted to the ICU for > 12 hrs, rapid volume infusions are common therapeutic interventions but the rapid volume infusions are typically small. The effect of a typical rapid volume infusion on hemodynamics and left ventricular areas in these patients is surprisingly small.