Continuous Fick cardiac output compared to thermodilution cardiac output

A system has been developed to monitor continuously the components of the oxygen Fick equation: oxygen consumption by a gas exchange analyzer and arteriovenous oxygen difference by pulse and fiberoptic oximetry. A computer-based system was developed which calculates cardiac output and other variables every 20 sec. Continuous Fick (CF) cardiac output was compared to thermodilution (TD) cardiac output in 21 ventilated post-cardiac surgery patients. A total of 237 simultaneous cardiac output measurements had a range between 2 and 11 L/min. The correlation between CF and TD cardiac outputs was r = .86, with an equation of TD cardiac output = 0.92 CF cardiac output + 1.16. There was a significant (p less than .001) difference between the two methods of cardiac output estimation. The CF method was consistently lower than TD; this difference was greater at lower flows. CF cardiac output measurement is practical; it offers distinct advantages in viewing cardiac output together with oxygen demand and oxygen extraction.     

Evaluation of a new continuous thermodilution cardiac output monitor in cardiac surgical patients: a prospective criterion standard study

OBJECTIVE: To evaluate the accuracy of a new continuous cardiac output monitor in critically ill patients. DESIGN: Criterion standard study. SETTING: Cardiac surgery intensive care unit in a university hospital. PATIENTS: Twenty cardiac surgical patients requiring intensive care treatment with pulmonary artery catheters after surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Cardiac output was monitored continuously with a modified pulmonary artery catheter that has a heating filament on the outside of the catheter. Four modes of data processing with different response times ("Normal," "Fast," "FastFilter," and "Urgent" modes) used by the monitoring system. A total of 240 determinations of cardiac output were performed using conventional bolus thermodilution technique; these results were compared with those obtained using three of the four continuous measuring modes available ("Normal," "FastFilter," and "Urgent"). Cardiac output ranged from 3.47 to 15.77 L/min (bolus thermodilution). The mean (bias) +/- SD of differences (precision) for all measurements was 0.40+/-1.26 L/min in the Normal mode (cardiac output <10 L/min: 0.34+/-0.66 L/min), 0.53+/-1.27 L/min in the FastFilter-mode (cardiac output <10 L/min: 0.60+/-0.75 L/min), and 0.63+/-1.34 L/min in the Urgent mode (cardiac output <10 L/min: 0.57+/-0.82 L/min). CONCLUSIONS: Continuous cardiac output measurement using the thermodilution technique is reasonably accurate, reliable, and applicable in routine clinical practice. The values obtained using the Normal mode of the monitor agreed significantly better with the conventional thermodilution method than the results of the two other modes studied (FastFilter and Urgent). In addition, measurements in two patients with cardiac output values of >10 L/min did not agree with the results of the bolus thermodilution method.     

Comparison of two impedance cardiographic techniques for measuring cardiac output in critically ill patients

The purpose of the present study was to compare cardiac output (Q) values obtained by both the Kubicek (MIC) and Sramek (NCCOM3) impedance cardiographic techniques with thermodilution (TD) in critically ill patients. The two impedance techniques were also compared in normal subjects. Seven healthy subjects and ten ICU patients were enlisted in the study. Three Q measurements were made in each subject. In the ICU patients, there were no significant differences in Q values as measured by TD (6.6 L/min), MIC (6.3 L/min), and NCCOM3 (6.4 L/min). Both MIC and NCCOM3 Q values were comparable to TD in patients. In normals, however, the NCCOM3 estimated larger values for Q than did the MIC (NCCOM3, 9.2 L/min; MIC, 6.2 L/min). Q values obtained with MIC in normals were comparable with published values for supine normals. Thus, the two techniques agreed in the patients but not in the normals. The reasons for these results are not obvious from the data, but are attributable to the measurements by the NCCOM3. Because of this, caution is suggested when interpreting absolute Q values obtained by the NCCOM3.     

Continuous measurement of cardiac output by the Fick principle: clinical validation in intensive care.

OBJECTIVE: To compare continuous measurement of cardiac output by the Fick principle with the thermodilution cardiac output technique in hemodynamically unstable patients. DESIGN: An open comparison of two methods. SETTING: Multidisciplinary ICU in a university hospital. PATIENTS: Eight patients after coronary bypass surgery and 13 patients with hyperdynamic septic shock. All patients were mechanically ventilated. MEASUREMENTS AND MAIN RESULTS: The continuous Fick cardiac output technique was compared with the thermodilution cardiac output using both warm and cold injection in the coronary artery bypass surgery patients and using warm injection only in the patients with hyperdynamic septic shock. The mean difference between the continuous cardiac output technique and all thermodilution measurements (n = 201) was 0.6 +/- 19%. There was a good correlation between the continuous cardiac output and the warm thermodilution technique (n = 125, r2 = .79; p less than .001). When consecutive measurements with warm and cold thermodilution were compared with the respective Fick-derived values (n = 76), the mean differences between the Fick-derived and the warm and cold thermodilution cardiac output values were 0.2 +/- 1.0 L/min and 0.3 +/- 1.0 L/min, respectively. The relationship between Fick-derived and both methods of thermodilution-derived cardiac output was relatively constant during different modes of ventilatory support. The correlation between the thermodilution measurements with cold and room temperature injectate was weak (r2 = .36; p less than .001), whereas a good correlation was observed between the respective Fick-derived values (r2 = .73; p less than .001). The mean difference between the warm and cold thermodilution cardiac output measurements was 0.1 +/- 1.1 L/min and between the corresponding Fick-derived measurements was 0.01 +/- 0.7 L/min. CONCLUSIONS: Continuous measurement of cardiac output by the Fick principle offers a convenient, reproducible method for hemodynamic monitoring of unstable patients. The variation between the two tested thermodilution techniques is likely to reflect relatively rapid dynamic variation of cardiac output, which is filtered in the 1-min average of cardiac output obtained by the continuous Fick technique.     

Esophageal electrodes allow precise assessment of cardiac output by bioimpedance.

OBJECTIVES: To analyze the impact of the position of the thoracic external electrodes on the values of cardiac output measured by electrical bioimpedance and to compare the results obtained by bioimpedance with those values determined by thermodilution in critically ill patients. DESIGN: Open, prospective, comparative trial. SETTING: ICU of a teaching hospital. PATIENTS: Twenty healthy volunteers and ten critically ill patients. INTERVENTIONS: Measurements of cardiac output by bioimpedance at rest and after physical activity in normal volunteers and after changing the neck or xiphoid electrodes. Comparisons of cardiac output obtained by thermodilution and bioimpedance with internal and external electrodes in patients. MEASUREMENTS AND MAIN RESULTS: Mean +/- SD values are presented. Cardiac output values at rest and after exercise were 6.7 +/- 1.3 and 10.8 +/- 2.6 L/min at rest and after exercise, respectively (p less than .001). Displacement of the xiphoid electrodes 3 cm in the caudal direction was accompanied by a decrease of the mean cardiac output from 7.1 +/- 1.2 to 5.8 +/- 1.3 L/min (p less than .001) and displacement 3 and 6 cm cranially was accompanied by increases in cardiac output from 7.1 +/- 1.2 to 8.1 +/- 1.4 L/min (p less than .001) and 8.6 +/- 1.5 L/min (p less than .001), respectively. In the ten patients, cardiac output measurements were virtually identical when results obtained by thermodilution (6.7 +/- 3.1 L/min) were compared with those results obtained by bioimpedance using internal esophageal (6.6 +/- 3.1 L/min), but not external (4.7 +/- 1.6 L/min) electrodes. CONCLUSIONS: a) The values of cardiac output derived from measurements obtained by bioimpedance using internal electrodes were comparable with those values derived from thermodilution. b) Values of cardiac output from bioimpedance studies with external electrodes were dependent on the position of the xiphoid electrodes.     

Mathematical coupling does not explain the relationship between right ventricular end-diastolic volume and cardiac output

OBJECTIVE: To evaluate the clinical significance of mathematical coupling on the correlation between cardiac output and right ventricular end-diastolic volume (RVEDV) through measurement of cardiac output by two independent techniques. DESIGN: Prospective, observational study. SETTING: Surgical intensive care unit in a level 1 trauma center. PATIENTS: Twenty-eight critically ill surgical patients who received mechanical ventilation and hemodynamic monitoring with a pulmonary artery catheter. INTERVENTIONS: A pulmonary artery catheter designed to measure right ventricular ejection fraction (RVEF) and cardiac output by the intermittent bolus thermodilution (TDCO) method and continuous cardiac output by the pulsed thermal energy technique was placed. A computerized data logger was used to collect data simultaneously from the RVEF/TDCO system and the continuous cardiac output system. MEASUREMENTS AND MAIN RESULTS: Two hundred forty-nine data sets from 28 patients were compared. There is statistical correlation between TDCO and continuous cardiac output measurements (r = 0.95, p < 0.0001) with an acceptable bias (-0.11 L/min) and precision (+/-0.74 L/min). The correlation was maintained over a wide range of cardiac outputs (2.3-17.8 L/min). There is a high degree of correlation between RVEDV and both TDCO (r = 0.72, p < 0.0001) and independently measured continuous cardiac output (r = 0.68, p < 0.0001). These correlation coefficients are not statistically different (p = 0.15). CONCLUSIONS: The continuous cardiac output technique accurately approximates cardiac output measured by the TDCO method. RVEDV calculated from TDCO correlates well with both TDCO and independently measured continuous cardiac output. Because random measurement errors of the two techniques differ, mathematical coupling alone does not explain the correlation between RVEDV estimates of preload and cardiac output.     

Near continuous cardiac output by thermodilution

A new thermodilution method for frequent (near continuous) estimation ofcardiac output, without manual injection of fluid into the blood, was tested.The method utilizes a pulmonary artery catheter equipped with a fluid filledheat exchanger. The technique is based on cyclic cooling of the blood in theright atrium and measurement of the temperature changes in the pulmonaryartery. Using this technique, a new estimate of cardiac output can be obtainedevery 32 s. Cardiac output estimates, obtained for a running mean of threemeasurements with this method, were compared to the mean of three conventionalthermodilution measurements. The measurements were obtained during shortperiods of stable respiration and circulation.In six pigs, we made 46 paired measurements of conventional thermodilution(TD) and near continous (TDc) thermodilution. The cardiac output(CO TD) ranged from 2.4–13.7 l/min (mean 5.4 l/min). Thebest linear fit through the paired data points was CO TDc =–0.57 + 1.01 CO TD. The mean difference between themethods was –0.50 l/min (S.D. = 0.39). The mean coefficient of variationof repeated measurements with the near continuous thermodilution was3.6%.Considering changes of more than 0.25 l/min to be significant, all changes incardiac output measured by conventional thermodilution were followed by therunning mean of three near continuous thermodilution estimates.This study demonstrates the feasibility of the new method to monitorcardiac output, and to detect all changes greater than 0.25 l/min.     

Evaluation of a noninvasive method for cardiac output measurement in critical care patients

OBJECTIVE: Thermodilution (TD) is the gold standard to monitor cardiac output (CO) in critical care. However, there is concern about the safety of right-ventricular catheterization. The CO(2) rebreathing technique allows noninvasive CO determination by means of the indirect Fick principle. Our objectives were: (a) to assess the accuracy of a new system of CO measurement using the CO(2) partial rebreathing method (PRCO); (b) to evaluate whether the PRCO itself may induce changes in CO. DESIGN AND SETTING: Prospective study in the intensive care department in a university-affiliated hospital. PATIENTS: Twenty-two mechanically ventilated critically ill patients. INTERVENTIONS: CO measured simultaneously by PRCO and TDCO. MEASUREMENTS AND RESULTS: PRCO and TDCO values were compared by concordance analysis. Stability of cardiac output during PRCO was evaluated by comparing the TDCO measurements before, during, and after the partial rebreathing period using analysis of variance. From a total of 79 valid sets of measurements, bias and precision was calculated at -0.18+/-1.39 l/min. The concordance analysis of lower and intermediate CO values (<7 l/min) yielded a bias and precision calculation of -0.07+/-0.91 l/min. No changes in hemodynamics were observed during the partial rebreathing period. CONCLUSIONS: The noninvasive partial CO(2) rebreathing technique may be an alternative method for CO determination in mechanically ventilated critically ill patients. The rebreathing maneuver alone does not induce changes in CO.     

Continuous noninvasive cardiac output as estimated from the pulse contour curve

We developed a noninvasive computer-based system for estimating continuous cardiac output by a modified pulse contour method using a finger pressure waveform. The method requires no individual patient calibration or baseline cardiac output. First, we calibrated the system in a learn group of 20 patients. The computer-based cardiac output was then compared with thermodilution cardiac output in 27 patients undergoing coronary artery bypass surgery. A total of 94 cardiac outputs were performed (three averaged per determination) at four predetermined time periods: preinduction, postinduction, prebypass, and postbypass. During determination of each thermodilution cardiac output, the pulse wave data were simultaneously recorded on cassette tape. The patients had cardiac outputs ranging from 2.9 to 6.4 L/min. The correlation coefficient was 0.75. The average thermodilution cardiac output was 4.50 (±0.83 SD) L/min, while the cardiac output derived from the finger pressure wave was 4.48 (±0.7 SD) L/min (95% confidence interval [CI] of difference, 0–3.2%). The mean difference between the two methods was 0.02 (±0.55 SD) L/min. The 95% CI for the bias was 0.0001 to 0.036 L/min. The 95% CI for the lower limit of agreement was – 1.12 to – 1.06 L/min; the upper limit for the 95% CI was 1.09 to 1.16 L/min. The program demonstrated that information about cardiac output can be obtained by using the Finapres device (Ohmeda, Boulder, CO). The cardiac output values obtained by this continuous noninvasive technique were within ±20% of the simultaneous thermodilution values 87% of the time. This was true over the narrow range of cardiac outputs (2.9 to 6.4 L/min) and wide range of heart rates (45 to 140 beats/min).     

Continuous noninvasive cardiac output as estimated from the pulse contour curve

We developed a noninvasive computer-based system for estimating continuous cardiac output by a modified pulse contour method using a finger pressure waveform. The method requires no individual patient calibration or baseline cardiac output. First, we calibrated the system in a learn group of 20 patients. The computer-based cardiac output was then compared with thermodilution cardiac output in 27 patients undergoing coronary artery bypass surgery. A total of 94 cardiac outputs were performed (three averaged per determination) at four predetermined time periods: preinduction, postinduction, prebypass, and postbypass. During determination of each thermodilution cardiac output, the pulse wave data were simultaneously recorded on cassette tape. The patients had cardiac outputs ranging from 2.9 to 6.4 L/min. The correlation coefficient was 0.75. The average thermodilution cardiac output was 4.50 (±0.83 SD) L/min, while the cardiac output derived from the finger pressure wave was 4.48 (±0.7 SD) L/min (95% confidence interval [CI] of difference, 0–3.2%). The mean difference between the two methods was 0.02 (±0.55 SD) L/min. The 95% CI for the bias was 0.0001 to 0.036 L/min. The 95% CI for the lower limit of agreement was – 1.12 to – 1.06 L/min; the upper limit for the 95% CI was 1.09 to 1.16 L/min. The program demonstrated that information about cardiac output can be obtained by using the Finapres device (Ohmeda, Boulder, CO). The cardiac output values obtained by this continuous noninvasive technique were within ±20% of the simultaneous thermodilution values 87% of the time. This was true over the narrow range of cardiac outputs (2.9 to 6.4 L/min) and wide range of heart rates (45 to 140 beats/min).     

Bioimpedance versus thermodilution cardiac output measurement: The bomed NCCOM3 after coronary bypass surgery

Values obtained for cardiac output (CO) were compared using thermodilution (TD) with those obtained using bioimpedance (Bi) as measured using the Bomed NCCOM3 (Revision 6) in 28 consecutive patients in the first 24h after coronary artery bypass surgery (CABS). In 46 paired measurements made in the first 12 h after CABS Bi values for CO were significantly lower than TD values, the limits of agreement between the two methods were also unacceptably large (mean Bi 4.38 (SD 1.40) l/min, mean TD 5.46 (SD 1.19) l/min, limits of agreement–3.05 to +0.89). In 55 paired measurements made after 12h (all in spontaneously breathing patients) there was no significant difference between the two methods and acceptable limits of agreement, mean Bi 5.69 (SD 1.2) l/min mean TD 5.6 (SD 1.2) l/min, limits of agreement–0.99 to +1.17). The significantly lower BiCO values obtained in the first 12h after CABS show that BiCO measurement is not consistently reliable in the intensive care setting.     

Thermodilution versus inert gas rebreathing for estimation of effective pulmonary blood flow

OBJECTIVE: To compare measurements of the effective pulmonary blood flow (Qep, i.e., nonshunted fraction of cardiac output, Qt) by the inert gas rebreathing (RB) method and the thermodilution (TD) technique in critically ill patients. DESIGN: Prospective, comparative study of a noninvasive method and an established invasive technique. SETTING: An 11-bed general intensive care unit in a university hospital. PATIENTS: A total of 14 critically ill patients, all mechanically ventilated and monitored with systemic and pulmonary artery catheters. MEASUREMENTS AND MAIN RESULTS: Qep was determined in duplicate by RB using a mass spectrometer for gas analysis. For each determination, Qt was measured in triplicate by the cold water bolus TD technique and averaged. Simultaneously mixed venous and arterial blood samples were analyzed to calculate the intrapulmonary shunt fraction and thereby convert estimates of Qt to Qep. Mean difference between paired estimates (RB - TD) was 0.01 L/min, so for differences was 1.19 L/min, and 95% confidence interval for the bias was -0.45 to 0.47 L/min. Coefficients of variation for repeated Qep estimates were 8% (RB) and 12% (TD), respectively. Coefficients of variation for RB estimates of functional residual capacity and lung tissue volume were 6% and 17%, respectively. CONCLUSIONS: The RB method is a promising method for simultaneous noninvasive estimation of Qep and functional residual capacity in mechanically ventilated patients. However, further investigations are needed to evaluate potential problems of the method before it can be recommended for clinical purposes.     

Determination of cardiac output based on breath-holding

A breath-holding method for determination of cardiac output is described. It is based on the indirect Fick principle applied to carbon dioxide. Mixed venous PCO2 (PvCO2) is measured noninvasively using a CO2 breath-holding technique and PaCO2 is obtained by arterial puncture. Partial pressures are converted into contents using each patient's CO2 dissociation curve, taking into account temperature, hemoglobin, arterial and venous pH. The authors have applied this method to the determination of cardiac output in 20 patients, in whom cardiac output was also measured invasively using either direct Fick or thermodilution method. Mean cardiac output determined using the breath-holding method was 5.48 +/- 2.95 (SD) L/min, compared to 5.54 +/- 2.88 L/min as determined by the direct Fick or thermodilution method. Good correlation was found between the invasive and breath-holding method (r = 0.97, p < 0.001). The authors conclude that cardiac output at rest may be estimated with considerable accuracy from the measurements of PaCO2, CO2 production and the breath-holding mixed venous PCO2 without right-sided cardiac catheterization.     

Continuous cardiac output monitoring via arterial pressure waveform analysis following severe hemorrhagic shock in dogs

OBJECTIVES: To determine agreement and correlation between cardiac output determined by arterial pressure waveform analysis (PulseCO) and the lithium dilution indicator technique (LiDCO) during severe hemorrhagic shock and after fluid resuscitation in dogs. DESIGN: Prospective experimental study. SETTING: University research laboratory. SUBJECTS: Twelve adult mongrel dogs. INTERVENTIONS: Dogs were anesthetized, and selected arteries and veins were catheterized. Baseline cardiac output was determined by LiDCO and used to calibrate the PulseCO. Hemorrhagic shock was induced by withdrawing blood to achieve and maintain a mean arterial pressure of 30-40 mm Hg for 60 mins, and cardiac output was measured again using both methods. All dogs were resuscitated by administering lactated Ringer's solution intravenously to achieve and maintain a mean arterial pressure between 60 and 70 mm Hg. PulseCO and LiDCO values were measured at 10 and 120 mins after resuscitation. MEASUREMENTS AND MAIN RESULTS: Mean baseline cardiac output was 2.93 +/- 0.45 L/min. PulseCO values overestimated cardiac output compared with LiDCO during hemorrhagic shock (2.25 vs. 0.78 L/min). There were no differences in cardiac output determined by PulseCO and LiDCO at 10 and 120 mins after fluid resuscitation. Bland-Altman analysis suggested that PulseCO values were inaccurate after hemorrhage, producing significant bias with wide limits of agreement and percentage error (1.47 +/- 1.46 L/min; 97%). Bias was small but the limits of agreement and percentage error were large for cardiac output at 10 and 120 mins after resuscitation (-0.1 +/- 1.88 [98%] and -0.17 +/- 1.32 [71%] L/min, respectively). There appeared to be a negative but not significant correlation after hemorrhage (r = -.45; p = .15). CONCLUSIONS: PulseCO determination of cardiac output does not accurately predict rapid decreases in cardiac output or the effects of fluid resuscitation in dogs. Recalibration of PulseCO may be necessary after any apparent or suspected decrease in cardiac preload, afterload, or contractility.     

Effects of injectate volume on thermodilution measurements of cardiac output in patients with low ventricular ejection fraction.

OBJECTIVE: To determine the effect of 5-mL injectate on cardiac output measurements in critically ill patients with low ventricular ejection fraction (< 35%). METHODS: Thermodilution cardiac output measurements obtained with three 5-mL and three 10-mL (randomly ordered) iced injectates in 50 patients with low ejection fraction were averaged if the measurements were within 10% of the median. If the 3 measurements were not within those limits, additional measurements were obtained. RESULTS: Cardiac output measured with the 5-mL injectate (mean, 4.63 L/min) and cardiac output measured with the 10-mL injectate (mean, 4.52 L/min) were not significantly different (P = .64). Lower and upper limits of agreement were -1.7 L/min to +1.6 L/min. The bias (mean difference between 10- and 5-mL measurements) of all measurements was -0.09, and the precision was 1.43 L/min, with a 95% confidence limit (mean difference +/- 2 SD) of -1.7 to +1.6 L/min. An additional measurement was necessary in 77% of patients in the 5-mL group but in only 48% of the 10-mL group (P = .006). CONCLUSIONS: Cardiac outputs measured with 5- and 10-mL injectates do not differ significantly. The greater variability of measurements obtained with a 5-mL injectate suggests that more measurements, and thus more time, are needed to measure cardiac output accurately. Clinicians must weigh the benefit of minimizing fluid volume used against the potential decreased reliability of cardiac output measurements.     

Cardiac output measurement by pulse dye densitometry: a comparison with the Fick's principle and thermodilution method

OBJECTIVE: To evaluate the agreement between cardiac output (CO) measurements obtained by a new dye dilution technique using pulse dye densitometry (PDD) and thermodilution (TD) and the direct Fick method (F). DESIGN AND SETTING: Prospective clinical study in a university hospital, cardiac surgery intensive care unit. PATIENTS: Fifty-eight cardiac surgery patients after admission to the intensive care unit (six were excluded due to a low pulse signal quality using the PDD method). MEASUREMENTS AND RESULTS: Mean CO was 5.3+/-1.8 l/min for PDD, 5.7+/-1.68 l/min for TD, and 6.16+/-1.66 l/min for F. There was a good correlation between PDD and TD ( r(2)=0.93) and between PDD and F ( r(2)=0.77). Bias and precision between PDD and TD were -0.39+/-0.5 l/min and -0.69+/-0.85 l/min between PDD and F. In general, PDD determined lower CO values than TD and F. Especially in patients with CO below 5 l/min PDD underestimated CO in comparison to TD and F (bias and precision: -0.51+/-0.40 l/min and -0.83+/-1.0 l/min). CONCLUSION: Comparison between PDD and TD showed good agreement for the normal to high CO range. However, agreement was poor in patients with low CO. In the latter patient group PDD showed relevant underestimation of CO compared to TD and F. Due to these limitations PDD cannot entirely replace the pulmonary artery catheter for CO determination.     

Doppler measurement of cardiac output during cardiopulmonary resuscitation.

OBJECTIVE: To estimate the cardiac output produced by external cardiac compression during standard cardiopulmonary resuscitation performed by two groups of operators with different levels of experience and training. METHODS: Cardiac output was measured by Doppler aortovelography. All patients included in the study had necropsy examinations. Only patients without evidence of pulmonary embolism, myocardial rupture, aortic valve disease, or acute depletion of the intravascular volume were included. RESULTS: 31 patients presenting to the accident and emergency department suffering from non-traumatic cardiac arrest had cardiac output measurements made during resuscitation. Eleven patients were excluded after necropsy examination. The median cardiac index for the 20 study patients was 3.2 L min-1 m-2. The cardiac output produced by massage by less experienced personnel (median 1.2 L min-1 m-2) was significantly less than that produced by those fully trained in the technique (median 3.2 L min-1 m-2; P < 0.01 95% confidence interval -2.36 to -1.29). The amount of resuscitation related trauma was no greater than in other published series. CONCLUSIONS: Differences in cardiac output during external cardiac compression are related to experience with the technique.     

Cardiac output determinations in the pig--thoracic electrical bioimpedance versus thermodilution

The accuracy of transthoracic electrical bioimpedance (TEB) for continuous, noninvasive measurement of cardiac output (Qt) in pigs was assessed in comparison with the thermodilution (TD) technique. Using the TEB technique, the different thoracic habitus of the pig had to be corrected for A good correlation with the TD technique was obtained (r = .87; p less than .001; n = 86) using thoracic length value (the measured value plus 25%) in an NCCOM3-R6 cardiodynamic computer for Qt values ranging from 2.9 to 9.8 L/min in pigs weighing from 40 to 75 kg. However, the Qt values given by the NCCOM3 were systematically 11% to 15% higher over the full range of values than the average of NCCOM-3 and TD Qt values. On the basis of the good agreement in the present study between the TEB and TD techniques over a broad range of Qt values, we conclude that TEB offers a valuable continuous, noninvasive alternative to TD for Qt determinations in experimental porcine models.     

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 heterogeneous population of critically ill patients.     

Cardiac output measurement in children: comparison of the Ultrasound Cardiac Output Monitor with thermodilution cardiac output measurement

OBJECTIVE: To compare the assessment of cardiac output (CO) in children using the noninvasive Ultrasound Cardiac Output Monitor (USCOM) with the invasive pulmonary artery catheter (PAC) thermodilution cardiac output measurement. DESIGN AND SETTING: Prospective observational study in a tertiary center for pediatric cardiology of a university children's hospital. PATIENTS: Twenty-four pediatric patients with congenital heart disease without shunt undergoing cardiac catheterization under general anesthesia. MEASUREMENTS AND RESULTS: CO was measured by USCOM using a suprasternal CO Doppler probe in children undergoing cardiac catheterization. USCOM data were compared to CO simultaneously measured by PAC thermodilution technique. Measurements were repeated three times within 5 min in each patient. A mean percentage error not exceeding 30% was defined as indicating clinical useful reliability of the USCOM. CO values measured by PAC ranged from 1.3 to 5.3 l/min (median 3.6 l/min). Bias and precision were -0.13 and 1.34 l/min, respectively. The mean percentage error of CO measurement by the USCOM compared to PAC thermodilution technique was 36.4% for USCOM. CONCLUSIONS: Our preliminary data demonstrate that cardiac output measurement in children using the USCOM does not reliably represent absolute CO values as compared to PAC thermodilution. Further studies must evaluate the impact of incorporating effective aortic valve diameters on CO measurement using the USCOM.