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An increase in free radical activity has been observed in patients suffering from a variety of illnesses and has been correlated with disease severity. Free radical production is increased by the administration of total parenteral nutrition (TPN) and may be linked to its adverse effects. Some of the complications of TPN can be ameliorated by partial enteral feeding. The aim of this study was to investigate free radical activity during critical illness and during the administration of parenteral nutrition.Three groups of surgical infants were studied: (1) control infants (n = 8) before minor surgery, (2) stable infants on the ward recovering from a major operation (n = 24), (3) critically ill infants in the neonatal intensive care unit (NICU, n = 28). Fourteen patients in the ward and 17 patients in NICU were receiving parenteral nutrition. Of the 31 patients on TPN, 9 were also receiving minimal enteral feeding (3% to 24% of total calorie intake). Plasma malondialdehyde (MDA), an index of free radical activity, was measured in all 60 infants. The Paediatric Risk of Mortality (PRISM) score was obtained on NICU patients. The cytokines tumor necrosis factor (TNF-alpha) and interleukin 6 (IL-6) were measured in 25 patients.Plasma MDA was significantly higher in (1) the stable patients on the ward compared with control patients (P.001) and (2) patients in NICU compared with stable patients in the ward (P.001). Parenteral nutrition was associated with higher levels of plasma MDA both in stable patients in the ward and critically ill infants in NICU. There was no correlation between the PRISM score and MDA. In patients not receiving TPN there is a correlation between MDA and TNF-alpha (r = 0.54, P = .02) and between MDA and IL-6 (r = 0.74, P = .001). The level of free radical activity in patients on TPN is not changed by partial enteral feeding.Critical illness causes a rise in free radical production. Parenteral nutrition causes a significant elevation in free radical activity in both stable infants in the ward and critically ill infants in NICU. The addition of minimal enteral feeding to parenteral nutrition does not reduce free radical activity. We hypothesize that the parenteral nutrition solution directly initiates free radical production.

The methods proposed by Nilsson-Ehle and Ekman [8] for the specific estimation of lipoprotein lipase and hepatic lipase activities in post-heparin plasma were investigated. The procedure for hepatic lipase was found to be specific, but the lipoprotein lipase assay required modification to abolish hepatic lipase interference. The modified procedures were fully validated and found to be relatively simple, rapid and specific and were used to investigate children with primary and secondary hyperlipidaemic states.