Endogenous morphine is produced in response to cardiopulmonary bypass in neonatal pigs

Background: Cardiopulmonary bypass (CPB) is associated with a systemic inflammatory response. Endogenous morphine production has previously been demonstrated in humans after cardiac surgery with CPB. It has been hypothesized that morphine plays a role as an anti-inflammatory mediator in the systemic inflammatory response. The aim of this study was to investigate if the CPB procedure in itself elicits an endogenous morphine production in neonatal pigs. Methods: Endogenous morphine production was measured in arterial blood in piglets exposed to sternotomy alone (sham group, n=10) or sternotomy and CPB (n=10). Blood samples were obtained immediately after the induction of anaesthesia, at the end of CPB and 4 h later. Morphine in arterial blood was detected by radioimmunoassay and confirmed by gas chromatography mass spectrometry. Results: Animals undergoing CPB showed detectable endogenous morphine concentrations immediately after CPB, with increased concentrations postoperatively. There was no measurable morphine production in the sham operated pigs. Conclusion: The CPB procedures elicits an endogenous morphine production in neonatal pigs. This morphine response is analogous to the previously demonstrated response in patients subjected to cardiac surgery and CPB. (C) Acta Anaesthesiologica Scandinavica 44 (2000).