The development of parenteral nutrition has been a major advance in the care of neonates undergoing surgery. However, long-term parenteral nutrition can result in complications, some of which may result from an increased free radical activity associated with the lipid component of the regimen. This thesis describes studies undertaken to determine the effects of total parenteral nutrition (TPN) on free radical formation in neonatal surgical patients. The parenteral nutrition regimen was then modified in an attempt to reduce free radical formation. Lipid peroxides and malondialdehyde (MDA), some of the products of free radical formation, were assayed in parenteral nutrition solutions. The mean lipid peroxide concentration was 19.25umol/l and the mean MDA concentration was 8.69umol/l. Neonates receiving TPN had significantly greater MDA concentrations than those not receiving TPN (p<0.0001). Stopping the lipid infusion resulted in a significant decrease in the mean plasma MDA concentration (p<0.01). Promoting oxidation of the administered lipid by reducing the carbohydrate to lipid ratio of the TPN also resulted in significantly decreased plasma MDA concentrations (p<0.01). The administration of a medium chain triglyceride emulsion was, however, associated with significantly greater plasma MDA concentrations than when a long chain triglyceride emulsion was used (p<0.05). Partial enteral feeding during parenteral nutrition did not have any significant effect on free radical activity. A relationship between free radical activity and illness severity in sick neonates was sought. There was no significant correlation between plasma MDA concentrations and the Paediatric Risk of Mortality (PRISM) score. However MDA concentrations showed a positive correlation with plasma TNF-a (p<0.05) and IL-6 (p<0.001) concentrations
