Ventricular function determination during extracorporeal membrane oxygenation (ECMO) following Norwood operation: a...

Extracorporeal membrane oxygenation has been used successfully to support both cardiac and pulmonary function following Stage I Norwood operation. Determination of the return of native cardiac function and pulmonary function can be easily accomplished because of the single ventricle physiology. The pulmonary function can be assessed while on full flow ECMO by isolating the membrane oxygenator gas compartment, allowing evaluation of native pulmonary gas exchange through the modified Blalock-Taussig shunt. Cardiac output can be calculated by using the following oxygen delivery equation: Total O2 delivery = ECMO oxygen delivery + ventricular oxygen delivery. The ventricular O2 saturation used in the formula for oxygen delivery is same as the mixed venous O2 saturation returning to the ECMO pump because of the large atrial communication following the Norwood operation. A 3.2 kilogram patient was placed on a pediatric ECMO circuit utilizing a heparin-coated centrifugal pump and a microporous membrane oxygenate after failure to wean from bypass because of a low oxygen saturation and poor ventricular function. On day 1 of support, the systemic arterial oxygen saturation was 100% and matched the ECMO arterial saturation. On day 2 of the support, the patient's arterial saturation decreased to 96%, and the ECMO mixed venous saturation was 87%. Using the oxygen delivery formula, the ventricular cardiac output was calculated to be 175 mL/min, with an ECMO flow of 400 mL/min for a total cardiac output of 575 mL/min. The native ventricular contribution was, therefore, 30% of total cardiac output. Calculation of cardiac output would normally require a left ventricular sample in a patient with biventricular physiology. The single ventricle physiology in the post-operative Norwood patient makes this calculation a useful tool for assessing return of ventricular function in these patients.