Efficacy of Flow Monitoring During ECMO

The hypothesis that blood flow monitoring could serve as an effective early indicator of distal obstruction during extracorporeal membrane oxygenation (ECMO) was tested under controlled experimental conditions. The ECMO circuit typically includes (or could be easily modified to include) a shunt that bifurcates from the main line returning a small amount of blood to the pump with access points for drug infusions. Distal circuit obstructions in the oxygenator and beyond will result in an increased diversion of flow from the distal line to the shunt. Thus, elevations in flow through the shunt can serve as a marker for distal circuit obstruction. An ECMO training circuit was adapted with a resistance chamber that simulates controlled and varying levels of distal obstructions. Experiments were conducted under pediatric and adult pump target flow rates simulating different levels of distal obstructions while documenting the shunt flow and pressure drop across the obstruction. There was measurable and statistically significant elevation in the shunt flow at all flow rates because of different levels of obstruction from baseline values and hence consistent with the hypothesis that shunt flow can serve as an indicator of distal obstruction in the ECMO circuit. Flow monitoring is over the tube, hands free, continuous, and easy to implement. Therefore, it has the potential to serve as an early nonspecific indicator of elevated distal resistance in the ECMO circuit, which can then trigger other measurements (such as pressure drop across the oxygenator) for a more specific assessment of the source for distal resistance.