Beschreibung:
<jats:p> Assessment of native cardiac output during extracorporeal circulation is challenging. We assessed a modified Fick principle under conditions such as dead space and shunt in 13 anesthetized swine undergoing centrally cannulated veno-arterial extracorporeal membrane oxygenation (V-A ECMO, 308 measurement periods) therapy. We assumed that the ratio of carbon dioxide elimination (V̇co<jats:sub>2</jats:sub>) or oxygen uptake (V̇o<jats:sub>2</jats:sub>) between the membrane and native lung corresponds to the ratio of respective blood flows. Unequal ventilation/perfusion (V̇/Q̇) ratios were corrected towards unity. Pulmonary blood flow was calculated and compared to an ultrasonic flow probe on the pulmonary artery with a bias of 99 mL/min (limits of agreement −542 to 741 mL/min) with blood content V̇o<jats:sub>2</jats:sub> and no-shunt, no-dead space conditions, which showed good trending ability (least significant change from 82 to 129 mL). Shunt conditions led to underestimation of native pulmonary blood flow (bias −395, limits of agreement −1,290 to 500 mL/min). Bias and trending further depended on the gas (O<jats:sub>2</jats:sub>, CO<jats:sub>2</jats:sub>) and measurement approach (blood content vs. gas phase). Measurements in the gas phase increased the bias (253 [LoA −1,357 to 1,863 mL/min] for expired V̇o<jats:sub>2</jats:sub> bias 482 [LoA −760 to 1,724 mL/min] for expired V̇co<jats:sub>2</jats:sub>) and could be improved by correction of V̇/Q̇ inequalities. Our results show that common assumptions of the Fick principle in two competing circulations give results with adequate accuracy and may offer a clinically applicable tool. Precision depends on specific conditions. This highlights the complexity of gas exchange in membrane lungs and may further deepen the understanding of V-A ECMO. </jats:p>