[Partial CO(2) rebreathing technique versus thermodilution: measurement of cardiac output before and after operations with extracorporeal circulation]

Nichtinvasives erweitertes hämodynamisches Monitoring

BACKGROUND

Cardiac output and the cardiac index (CI) are not routinely monitored during major abdominal surgery for economic as well as medical reasons. This practice, however, might be changed by the application of newer non-invasive technologies like the partial CO(2) rebreathing method based on the inverse Fick's principle. In this prospective randomized study we investigated the impact of a non-invasive monitoring of CI on the incidence of hemodynamic instability and interventions by the attending anesthesiologist during major abdominal surgery.

PATIENTS AND METHODS

Additionally to routine hemodynamic monitoring we measured CI using the partial CO(2) rebreathing method in 28 patients (9 female, 19 male) undergoing major abdominal surgery. In group I the anesthesiologists were aware of the results of the extended hemodynamic monitoring and in group II the attending anesthesiologist was blinded to the information obtained by these measurements of CI.

RESULTS

Groups did not differ with regard to the baseline hemodynamic parameters. We obtained 923 measurements in both groups and 95 situations of hemodynamic instability (CI<2.5 l/minxm(2)) were detected in group I compared to 147 situations in group II (p<0.05). There were significantly more hemodynamic interventions in group I than in group II (p<0.0001). The cardiac index remained higher in group I in comparison to group II (p<0.0001). Measurement of CI was the only method to detect situations of hemodynamic instability in our setting.

CONCLUSION

The incidence of hemodynamic instability was significantly reduced during major abdominal surgery when anesthesiologists were aware of the measurement results of extended hemodynamic monitoring.

Evaluation of a noninvasive cardiac output monitor in mechanically ventilated children

OBJECTIVE

To compare measurements of cardiac output (CO) and cardiac index (CI) obtained by a recently developed noninvasive continuous cardiac output system, NICO (CONICO), and transthoracic Doppler echocardiography (COTTE) in mechanically ventilated children.

DESIGN AND SETTING

Prospective study in a university-affiliated tertiary pediatric intensive care unit.

PATIENTS

A total of 21 mechanically ventilated children, weighing >15 kg, in stable respiratory and hemodynamic condition.

MEASUREMENTS

Sets of three successive measurements of CO with the NICO system and transthoracic Doppler echocardiography were obtained. Bland-Altman analysis was used to compare the agreement between the two methods.

RESULTS

The mean +/- sd CO values were 4.06 +/- 1.43 L/min for CONICO and 4.67 +/- 1.78 L/min for COTTE. Bias +/- sd between the two methods was -0.61 +/- 0.94 L/min. The variability of the difference between the two methods increased as the magnitude of the CO measurement increased. Similar results were obtained for cardiac index: 4.01 +/- 1.40 L.min.m for CINICO and 4.59 +/- 1.48 L.min.m for CITTE. Bland-Altman analysis revealed a nonuniform relationship between CI difference and the magnitude (y = -0.299 - 0.0655 x mean). The variability of the differences did not increase as the magnitude of the CO measurement increased (sd of estimate was 0.827 L.min.m). With both CONICO and CINICO, each measurement was highly repeatable, with coefficient of variation of only 2.88% +/- 2.31%. Repeatability with Doppler echocardiography was 7.02% +/- 4.33%.

CONCLUSIONS

The NICO system is a new device that measures CO easily and automatically in mechanically ventilated children weighing >15 kg. CO values obtained with this technique were in agreement with those obtained with Doppler echocardiography in children in respiratory and hemodynamic stable condition. The NICO system needs further investigation in children in unstable respiratory and hemodynamic condition.

Comparison between cardiac output values measured by thermodilution and partial carbon dioxide rebreathing in patients with acute lung injury

CONTEXT

Thermodilution, which is considered to be a standard technique for measuring the cardiac output in critically ill patients, is not free from relevant risks. There is a need to find alternative, noninvasive, automatic, simple and accurate methods for monitoring cardiac output at the bedside.

OBJECTIVE

To compare cardiac output measurements by thermodilution and partial carbon dioxide rebreathing in patients with acute lung injury at two levels of severity (lung injury score, LIS: below 2.5, group A; and above 2.5, group B).

TYPE OF STUDY

Comparative, prospective and controlled study.

SETTING

Intensive Care Units of two university hospitals.

METHODS

Cardiac output was measured by thermodilution and partial carbon dioxide rebreathing. Twenty patients with acute lung failure (PaO2/FiO2 < 300) who were under mechanical ventilation and from whom 294 measurements were taken: 164 measurements in group A (n = 11) and 130 in group B (n = 9), ranging from 14 to 15 determinations per patient.

RESULTS

There was a poor positive correlation between the methods studied for the patients from groups A (r = 0.52, p < 0.001) and B (r = 0.47, p < 0.001). The application of the Bland-Altman test made it possible to expose the lack of agreement between the methods (group A: -0.9 +/- 2.71 l/min; 95% CI = -1.14 to -0.48; and group B: -1.75 +/- 2.05 l/min; 95% CI = -2.11 to -1.4). The comparison of the results (Student t and Mann-Whitney tests) within each group and between the groups showed significant difference (p = 0.000, p < 0.05).

DISCUSSION

Errors in estimating CaCO2 (arterial CO2 content) from ETCO2 (end-tidal CO2) and situations of hyperdynamic circulation associated with dead space and/or increased shunt possibly explain our results.

CONCLUSION

Under the conditions of this study, the results obtained allow us to conclude that, in patients with acute lung injury, the cardiac output determined by partial rebreathing of CO2 differs from the measurements obtained by thermodilution. This difference becomes greater, the more critical the lung injury is.

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

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