Is Morphine Superior to Fentanyl for Analgesia during Extracorporeal Membrane Oxygenation in Adult Patients?

Abstract

Introduction: Studies investigating the increased sedation and analgesic requirements during neonatal extracorporeal membrane oxygenation (ECMO) have reported significant sequestration of these drugs in the ECMO circuit. However, there is no such data to guide therapy in adults. Our aim was to study the disposition of morphine and fentanyl in simulated ECMO circuits. Methods: Four identical extracorporeal circuits were set up using the standard component set used in Australia and New Zealand for ECMO in adult patients (pump-Jostra Rotaflow™ & oxygenator-Quadrox™, Maquet, Germany). The circuit was primed with crystalloid, albumin and human whole blood (<5 day old) and was maintained at a physiological PH and temperature for 24 h. Morphine (0.1 mg) and fentanyl (10 mcg) were injected post oxygenator at the start of the experiment. Serial post oxygenator blood samples were obtained for PK analysis. Plasma samples were assayed using a validated LC–MS/MS assay method. Results: Forty samples were analysed. Significant sequestration of fentanyl occurred in all four circuits (figure) with 67% of the drug lost in the circuit at 1 h (p < 0.05) and 96% at 24 h (p < 0.05). There was no significant sequestration of morphine in the circuit with 99% of the drug recovered from all circuits at 24 h.Conclusions: This difference in disposition of fentanyl and morphine in ECMO circuits probably reflects at least in part, the higher lipophilicity of fenanyl compared with morphine. Clinical studies comparing these two agents are indicated prior to recommending morphine as a first line drug for analgesia during ECMO