Determination of heat gain in the inferior vena cava during thermodilution measurements

The measurement of blood flow in the inferior vena cava (IVC) by thermodilution may be useful in the determination of hepatic venous blood flow (HVBF), but is subject to major errors. The most serious error is gain of heat from the abdominal viscera by the cool thermodiluent bolus as it moves up the IVC. The determination or elimination of this heat gain is necessary for accurate IVC blood flow measurement. By comparison of the area under the curve (AUC) for cardiac output following femoral vein injection of the thermodiluent bolus to the AUC following right ventricular injection of the thermodiluent, it is possible to quantitatively determine the unidirectional heat gain by the bolus at it moves up the IVC. The heat gain varied from 0 to 40% of the thermodiluent injected. The factors that aggravated the heat gain were a low cardiac output (below 4000 ml/mn), a large thermodiluent calorie load (over -40 calories), and possibly a slow transit time. The error due to heat gain may be effectively eliminated by keeping the size of the thermodiluent bolus below 40 negative calories.