Thermodilution cardiac output determination in the guinea pig

Thermodilution cardiac output was compared with simultaneously determined aortic flow in 5 guinea pigs during thoracotomy. Total cardiac output was affected by volume expansion, adrenergic stimulation, and the volume of hemorrhage. For the equation y = mx, where y is aortic flow, x is thermodilution cardiac output, and m is the slope of the regression line, m = 0.88 +/- 0.02 (95% confidence interval). The SE of the regression was 27.8 ml/min. Thermodilution may have been overestimated because the aortic flow measurement did not take into account the coronary arterial blood flow, which is approximately 4% of total cardiac output in the guinea pig. Indicator loss (ie, temperature) also may be an important factor in the calculation of cardiac output, as determinations of thermodilution cardiac output were affected by sampling site in the guinea pig. Thermodilution appears to be a useful and reliable means of determining cardiac output in the guinea pig.