In vitro clearance of intravenous acetaminophen in extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is a life support system used as a bridge to transplantation in critically ill patients who suffer from acute respiratory or cardiac failure with resultant hypoxemia and tissue hypoxia. This is not amendable to conventional support intervention. Previous studies have shown significant drug losses in the components of an ECMO circuit, leading to decreased plasma drug levels. An in vitro study was conducted to determine: (1) changes in intravenous acetaminophen levels over time and (2) changes in concentration observed between different sites of the ECMO circuit. A single bolus dose of intravenous (IV) acetaminophen was injected into a standard blood-primed ECMO circuit. Plasma drug concentrations in the circuit were then measured at specific time points at three different locations to determine concentrations of the drug at time 0, 15, 30, 60, 240 and 360 minutes. The three samples were drawn pre- and post-membrane oxygenator and the polyvinyl chloride (PVC) tubing. A second bolus dose was administered 24 hours after the first in order to compare "new" and "old" circuits. This entire process was repeated a total of three times. The results show that acetaminophen concentrations do not change significantly over time, with consistent levels seen in both new and old circuits (N=9). Average old circuit concentrations were approximately two times greater than the average new circuit concentrations after the circuit was re-dosed at 24 hours. Drug sequestration in the circuit was not significant in any of the three sites measured. It appears that, while acetaminophen levels remain relatively constant over a six hour period, dosing adjustments may be required for use in a circuit beyond the initial 24 hour period, depending on physiologic clearance of the drug. Assuming a six-hour dosing interval, levels should remain constant.