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

The NICO(2) monitor determines "pulmonary capillary blood flow" (Qpc) and cardiac output (Qt) using the "partial CO(2) rebreathing technique". The agreement between NICO(2) and thermodilution (TD) cardiac output was compared before and after cardiac surgery with cardiopulmonary bypass (CBP). In addition, the possibility of calculating the intrapulmonary shunt fraction (Qs/Qt) by combining data from the NICO(2) monitor and the TD was investigated.

In 32 patients measurements were made following induction of anesthesia ("pre-CBP"), 30 min after weaning from CBP ("post-CBP"), and 6-8 h after surgery ("post-OP"). Qt was determined by the NICO(2) monitor and TD, Qpc by the NICO(2) monitor, and Qs/Qt(O(2)) from the standard formula. An intrapulmonary shunt was calculated using Qpc(NICO(2)) and Qt(TD) according to the equation Qs/Qt=1-Qpc/Qt. Bland-Altman and regression analysis techniques were used for statistical evaluation.

"Pre-CBP" there was a good agreement between Qt(NICO(2)) and Qt(TD) with both a bias and precision of -0.13+/-0.46 l/min and a correlation of r=0.88+/-0.47 ( p<0.001). In contrast, "post-CBP" and "post-OP" there was a lack of agreement for Qt (bias and precision: 0.97+/-1.05 l/min and -0.33+/-0.8 l/min, respectively). Regarding the shunt calculations no significant correlations between methods could be found.

Cardiac output measurement by the NICO(2) monitor agree well with TD under steady-state conditions but after CBP the agreement was too small. Combining Qpc(NICO(2)) and Qt(TD) does not offer a reliable possibility for calculating intrapulmonary shunt.