A comparative evaluation of thermodilution and partial CO2 rebreathing techniques for cardiac output assessment in critically ill patients during assisted ventilation

Objective: To evaluate the reliability and clinical value of partial noninvasive CO(2) (NICO(2)) rebreathing technique for measuring cardiac output compared with standard thermodilution in a group of intensive care nonpostoperative patients. Design and setting: Clinical investigation in a university hospital ICU. Patients: Twelve mechanically ventilated patients with high (n =6) and low (n =6) pulmonary shunt fractions. Measurements and results: Thirty-six paired measurements of cardiac output were carried out with NICO(2) and thermodilution in patients ventilated in pressure-support mode and sedated with a sufentanil continuous infusion to obtain a Ramsay score value of 2. The mean cardiac output was: thermodilution 7.27+/-2.42 1/min; NICO(2) 6.10+/-1.66 1/min; r(2) was 0.62 and bias -1.2 1/min+/-1.5. Mean values of cardiac output were similar in the low shunt group (Qs/Qt < 20), with r(2)=0.90 and a bias of 0.01 l/min +/- 0.4; conversely, in. the. high pulmonary shunt group (Qs/Q > 35%) the mean was 9.32+/-1.23 l/min with thermodilution and a mean NICO(2)CO value was 6.97+/-1.53 l/min, with r(2) of 0.38 and a bias of -2.31+/-1.2 min. Conclusions: The partial CO(2) rebreathing technique is reliable in measuring cardiac output in non-postoperative critically ill patients affected by diseases causing low levels of pulmonary shunt, but underestimates it in patients with shunt higher than 35%.