Comparison of two thermodilution devices for postoperative care in patients with aneurysmal subarachnoid hemorrhage

Objective

In the postoperative care of patients with severe aneurysmal subarachnoid hemorrhage, a pulmonary artery (PA) catheter is highly recommended for guiding the appropriate hyperdynamic volume management. We prospectively evaluated the accuracy of cardiac output (CO) measurements of a new device for continuous CO monitoring based on transpulmonary thermodilution detected in a femoral artery line against the known gold standard of a PA catheter.

Methods

Ten patients presenting with high-grade aneurysmal subarachnoid hemorrhage were monitored in their postoperative course. CO measurements were obtaken simultaneously via a PA catheter and the transpulmonary thermodilution CO device. After calculating the accuracy of the new device, the obtained data of CO and cardiac preload values, wedge pressure and intrathoracic blood volume index (ITBI), were related to the patients final outcome.

Results

In 183 parallel measurements of CO, the correlation coefficient R² of both devices for CO and systemic vessel resistance was 0.88. Mean difference between the two devices was 0.02 ± 0.78 l/min. Absolute values of CO ranged from 3.1 to 15.6 l/min. Comparing the ITBI obtained from the new device (mean 912 ± 136 ml/m², within normal range) with known pulmonary capillary wedge pressure values (mean 14.4 ± 5.2 mmHg, above normal range) resembled that preload was overestimated when solely regarding wedge pressure. There was no correlation of both preload parameters (R² = 0.001). Albeit a small sample size, both mean CO and wedge pressure correlated significantly with the patients final outcome. However, best differentiation of final outcome states was obtained with mean ITBI.

Conclusions

The reliability for CO measurements of the new transpulmonary thermodilution device is high when compared with the gold standard of a PA catheter. The measuring device is far less invasive than a PA catheter and simple in handling. Although still to be validated by a larger database, guiding hyperdynamic volume therapy with filling volumes rather than filling pressures seems promising.