Background: During stress free fatty acids (FFA) from lipolysis exceeds oxidation and are partially incorporated in plasma lipids. Objectives: compare the FSR of triglycerides(TG), phospholipids (PL), and sterol ester (SE) in critically ill infants measured by the incorporation of PA or LA and to study if FSR correlate with the Rate of appearance (Ra) of the FFA (lipolysis).Subjects: 6 critically ill infants, receiving no oral feeding and 5 g·kg-1·day-1 of IV glucose. Median weight was 3.4kg (range 1.9-5.8) and age 23d (range 1-149)Interventions Albumin bound U13C-PA and U13C-LA were infused for 24 h. Blood was taken at 6, 12, 18, 24 h from the start of the infusion. PA and LA isotopic enrichment (IE) in FFA, TG, PL and SE were determined by GC-MS. FSR were calculated from the IE of PA and LA of plasma lipids (products) and IE of PA and LA in FFA (precursors).Results: The IE of PA and LA in FFA were at plateau throughout the study. Main results are in table: The FSR of TG, PL and SE calculated either with PA or LA were rather similar and they all correlated significantly with their respective Ra and FFA plasma concentrations. FSR were lowest for SE, intermediate for TG and highest for PL(not significant). Conclusions: In critically ill infants FSR of lipid classes can be masured either with PA or LA, FSR correlate significantly with lipolysis.

Table 1
Full size table