Viability of Extracorporeal Membrane Oxygenation Circuits during Arterio-venous Shunting: An Observational Study of ECMO Circuits

Trial off veno-arterial extracorporeal membrane oxygenation is often performed by diversion of circuit flow through an arterio-venous shunt. Separation from the patient presents an augmented risk for microbiological growth and deterioration of the circuit components and blood circulating within it. It is unclear how long mechanical components and blood circulating within the circuit remain intact during arterio-venous shunting.

Following decannulation, the arterial and venous lines were connected simulating an arterio-venous shunt. Flow was maintained at 500 ml/min. Observations at 11 intervals were paired with blood culture, blood gases, chemistry and coagulation studies. Heparin was not provided in two circuits, and four circuits received 30 IU/hour.

Of six circuits studied, five maintained flows of 500 ml/min for 48 hours. One circuit developed extensive clot after two hours and blood flow ceased. Microbial growth was not detected. Glucose, fibrinogen and platelet levels reduced progressively from the outset. Cell breakdown was evident by four hours (increase in plasma potassium and phosphate) and lactate rose above 6.3 mmol/L at four hours in all circuits.

Arterio-venous shunting longer than four hours carries a risk of blood decomposition and cell energy pathway depletion. Re-establishing extracorporeal membrane oxygenation support post arterio-venous shunting carries a risk of physiological derangement, given the blood composition changes during arterio-venous shunting. Consideration should be given to an alternate method to assess the physiological stability of patients off extracorporeal membrane oxygenation prior to decannulation. Alternately, consider a crystalloid flush of the circuit to remove decomposed blood if the trial-off exceeds four hours.