Thermodilution cardiac output may be incorrect in patients on venovenous extracorporeal lung assist.

Abstract

Cardiac output measurement is part of routine monitoring in critically ill patients. In patients on extracorporeal lung assist, thermodilution cardiac output measurement may lead to erroneous results caused by indicator loss into the extracorporeal circuit. Seven patients on venovenous extracorporeal lung assist were studied using different extracorporeal blood flows. We compared conventional thermodilution cardiac output determinations with dye dilution cardiac output measurement, with dye injection into the pulmonary artery. The latter method is not affected by the extracorporeal circuit. The conventional thermodilution method overestimated cardiac output up to a maximum of 300%, providing results up to 10 L/min higher than true cardiac output. The mean difference between thermodilution and true cardiac output as determined by dye dilution with pulmonary artery indicator injection was 3.0 +/- 2.41 L/min. There was no correlation between thermodilution cardiac output values and true cardiac output (r = 0.06). We conclude that conventional thermodilution is not a suitable method for cardiac output measurement in patients on extracorporeal lung assist, especially if high extracorporeal blood flows are applied.

Transpulmonary thermodilution measurements are not affected by continuous veno-venous hemofiltration at high blood pump flow

“…This might indicate that the blood flow rate of the extracorporeal circuit is too low compared to cardiac output for inducing a significant alteration in the thermal effect of the cold boluses. This hypothesis is in accordance with previous observations that showed that the ratio of extracorporeal blood flow to cardiac output plays an important role in thermodilution accuracy during extracorporeal veno-venous lung assist for acute respiratory distress syndrome [17,18]. The higher this ratio, the higher the overestimation of cardiac output by thermodilution.…”

Common pitfalls and tips and tricks to get the most out of your transpulmonary thermodilution device: results of a survey and state-of-the-art review

“…In extracorporeal lung assist systems, due to indicator loss in the extracorporeal circuit, cardiac output measurement as assessed by TPTD has been reported to be erroneously high, especially when high extracorporeal blood flows are applied [91,92]. However, some reports suggest that EVLWI measurement is reliable if extracorporeal blood flow does not exceed 20% of cardiac output [91,93]. The effects of an extracorporeal circuit are probably more pronounced if CO is low and the blood flow over the circuit is high (blood flow during continuous veno-venous haemofiltration (CVVH) is generally around 150−180 mL min -1 , compared to 450 mL min -1 during dialysis and 3 or more L min -1 during extracorporeal membrane oxygenation (ECMO).…”

Cardiac Output Monitoring Using Indicator-Dilution Techniques: Basics, Limits, and Perspectives

“…Conductive rewarming of indicator by surrounding tissue is more pronounced in low-flow states or when the indicator travels longer distances en route to the arterial thermistor 35 ; a classic example is the distance traveled by the indicator with TCPTD compared with the IB-PATD. These losses can lead to falsely increased COs. Overestimates of CO can also occur with mass diversion of cold indicator from its normal itinerary through the right heart, which can occur with a right-to-left intracardiac shunt, venovenous extracorporeal lung assist, 36 or certain instances of tricuspid regurgitation (TR) (see discussion below).…”