An evaluation of methods to monitor infants receiving intravenous lipids

Nephelometric measurement of light-scattering index and visual estimates of turbidity have been advocated to monitor serum Intralipid levels. This study describes a simple modified fluorometric method for accurately measuring lipid particles in serum and examines the reliability of such estimates compared with other chemical measurements. Ten percent IL was diluted with either saline or serum to various concentrations (0 to 250 mg/dl). The LSI showed an excellent correlation with known IL standard solutions in saline or serum (R = 0.99) and with triglyceride concentrations (R= 0.98). One hundred nine blood samples were obtained from 35 patients (28 neonates) receiving IL. An elevated TG, free fatty acid, or cholesterol level could not be reliably predicted from the LSI. The ability of clinical personnel to visually grade the degree of turbidity was evaluated by having them assign a turbidity score of 0 to 4+ to 39 hematocrit tubes which contained clear, hemolyzed, or icteric serum, each of which had IL concentrations varying from 0 to 292 mg/dl. The 15 tubes of identical IL concentration of 99 mg/dl were graded from 0 to 4+ by two of the observers, from 1 to 4+ by three of the observers, and 0 to 3+, 1 to 3+, and 2 or 3+ by one each of the observers. This study shows that (1) in vitro fluorometric LSI correlates well with IL concentrations; (2) in vivo correlations of LSI with FFA, cholesterol, and TG are poor; and (3) personnel are unable to reliably grade turbidity by visual examination of hematocrit tubes. Infants on IL should be monitored by TG and FFA levels.