Eighteen-percent of extracorporeal membrane oxygenation (ECMO) therapy experience oxygenator-related complications resulting in 40 to 80% mortality for those patients. Clinical researchers at the University of Iowa found that pediatric ECMO patients over the last decade had a greater incidence of and higher mortality associated with oxygenator clotting (22.4%) compared with adult ECMO patients (7.5%). One effective strategy to identify oxygenator-specific problems in an ECMO circuit is to monitor, hourly, the pressure drop across the oxygenator. However, pressure monitoring does not decipher other sources of distal circuit obstructions.

The clinicians adapted an ECMO circuit with a resistance chamber that simulated controlled and varying levels of distal obstructions to test their hypothesis that distal circuit obstructions would result in an increased diversion of flow from the distal line to the shunt thus elevating shunt flow which would then serve as a marker for a distal circuit obstruction. Experiments were conducted with measurements at 500, 1000, 1500, 2000, 3000, 4000 and 5000 mL/min pump target flow rates to simulate different levels of distal obstructions in the different size patients. Shunt flows and pressure drops across the obstruction were documented at each flow rate.

The results showed measurable and statistically significant elevation in the shunt  flow at all flow rates due to different levels of obstructions. The investigators therefore concluded that shunt flow elevations can serve as an indicator of distal obstruction in the ECMO circuit and flow monitoring can serve as an early nonspecific warning of elevated distal resistance anywhere in the ECMO circuit. This, in turn, can trigger other measurements such as pressure drop across the oxygenator for a more specific assessment of the source for distal resistance. Moreover, the clinicians state that Transonic flow monitoring is non-invasive, maintains sterility of the circuit, and is easy to implement. It is continuous and operator-free while pressure monitoring is not.

Badheka A, Stucker SE, Turek JW, Raghavan ML, "Efficacy of Flow Monitoring During ECMO," ASAIO J. 2017; 63(4): 496-500.