In vitro evaluation of sedative drug losses during extracorporeal membraneoxygenation

Sedative agents are routinely administered to critically ill patients, both on and off extracorporeal membrane oxygenation (ECMO), to enable patients to be comfortable and facilitate patient management. It has been observed e mpirically in our paediatric intensive care unit that doses of sedative dru gs required to achieve desired levels of sedation in ECMO patients are far greater than those used in non-ECMO patients. These differences could not s imply be accounted for by differences in patient types, clinical status or sedation levels. We therefore undertook an in vitro evaluation of drug bind ing in ECMO circuits. This study investigated how the polyvinyl chloride (PVC) and silicone rubbe r components of neonatal ECMO circuits affect drug delivery in patients thr ough drug sorption. Phase 1 investigated drug uptake by the two polymers in static solutions of known concentrations of four commonly used sedative dr ugs: lorazepam, midazolam, diazepam and propofol. Phase 2 involved the sett ing up of a complete neonatal ECMO circuit, injecting the drug solutions pr e-reservoir at a flow rate of 350 ml/min and collecting samples post-oxygen ator for analysis. Phase 1 results revealed significant uptake of drugs with losses in the ran ge 40-98% and in the order propofol > diazepam > midazolam > lorazepam. Pha se 2 results were similar acid in the first 40 min of running an ECMO circu it only 10% of propofol passed through the circuit. These results may help to explain observed clinical phenomena and raise important issues regarding drug dosing in ECMO patients.