Fat emulsion tolerance in very low birth weight neonates: effect on diffusion of oxygen in the lungs and on blood pH.

Forty-one very low birth weight neonates (820 to 1,510 g and 27 to 34 weeks of gestation) requiring total parenteral nutrition were randomly assigned to one of three regimens of administration of fat emulsion for a period of eight days. Groups I and II received the emulsion at a constant rate for, respectively, 24 and 16 hours, beginning with a daily dosage of 1 g/kg and increasing daily by 1 g/kg to a maximum of 4 g/kg. Group III received the emulsion at a constant rate or 4 g/kg for 24 hours. Blood pH and alveolar-arteriolar gradient of oxygen diffusion in the lungs were measured at regular intervals. The various regimens and rates of fat infusion appeared to have no deleterious effect on blood pH and alveolar-arteriolar oxygen diffusion gradient. Infusion rates as used in the study for appropriate for gestational age very low birth weight neonates appear to be safe, although caution is always warranted when dealing with tiny neonates whose pulmonary reserve is minimal. In view of data from other studies, it is suggested to infuse fat at a constant rate for 24 hours to avoid overloading the clearance mechanisms of fat particles from plasma.

Medium-chain triglycerides in neonatal nutrition. Absence of inhibition of lipogenesis and of laxative effect.

Eighteen neonates ranging in birthweight from 820 to 1570 gm and in gestational age from 29 to 35 weeks were assigned alternately and blindly to feedings with formulas containing 14 or 50% of their fat as medium-chain triglycerides (MCT). Mean daily intakes of formula and mean daily weight gains were similar in neonates in the two groups. Consistency of stools and mean weekly increments in skinfold thickness were not affected by the MCT content of the formula. This suggests that under ordinary clinical conditions, medium-chain triglycerides exert no laxative effect nor affect adversely the deposition of subcutaneous fat in very low-birthweight neonates.

Lipids in plasma of enterally-fed very low-birthweight neonates.

Plasma lipid patterns (total lipids, free glycerol, triglycerides, free fatty acids, and cholesterol) were studied in 10 very low-birthweight neonates assigned alternately to continuous drip versus every 2-hr bolus feedings with a formula containing 50% of its fat as medium-chain triglycerides. In the group of neonates fed continuously, plasma lipids did not vary significantly during the 4-day study. In the bolus-fed group, free fatty acid concentrations peaked 30 min after feeding; the other fractions did not vary significantly during 2 hr after feeding. Mean plasma concentrations of total lipids and triglycerides were higher in the continuous than in the bolus-fed neonates; concentrations of the other fractions were similar. Compared to plasma concentrations measured in a group of 4-day-old very low-birthweight neonates before any exposure to exogenous fat, continuously fed neonates had higher total lipid, triglyceride, free fatty acid, and cholesterol concentrations; bolus-fed neonates only had significantly higher triglyceride levels. These data emphasize the need to obtain information on plasma lipid patterns that is specific for gestational maturity, postnatal age, and method and type of feeding.

Dilution kinetics of chemicals used for estimation of water content of body compartments in perinatal medicine.

Dilution kinetics of markers commonly used for estimation of body water content and distribution in perinatal medicine (p-aminohippurate, inulin, antipyrine, H218O, bromide, and T1824) were studied in pregnant and neonatal baboons. Amniotic fluid concentrations of p-aminohippurate and inulin decreased exponentially after intraamniotic injection of these markers; from 2-24 h after injection, concentrations decreased linearly on semilogarithmic plot (r = 0.96-1.00). Plasma concentrations of antipyrine decreased exponentially during the first 60 min after intravenous injection, then linearly from 1-5 h (r = 0.92-0.90). Plasma concentrations of 18O decreased linearly from 1-6 h after injection in three or four cases (r = 0.94-0.99). Plasma concentrations of bromide decreased during the first 2 h after injection, then stabilized for at least 3 h. Plasma concentrations of T1824 decreased linearly from 10-60 min after intravenous injection (r = 0.97-1.00). Then the decline became exponential until 5 h. These data allow us to make specific recommendations regarding the optimal time and method of amniotic fluid and blood sampling during body water studies.

Influence of intravenous fat emulsion on serum bilirubin in very low birthweight neonates.

Thirty nine very low birthweight neonates (with a birth weight of 820 to 1500 g and gestation of 27 to 34 weeks) who required total parenteral nutrition were randomly assigned to one of three regimens of administration of fat emulsion for a period of eight days. Groups 1 and 2 received the emulsion at a constant rate over 24 and 16 hours, respectively, beginning with a daily dosage of 1 g/kg and increasing daily by 1 g/kg to a maximum of 4 g/kg. Group 3 received the emulsion at a constant rate of 4 g/kg a day over 24 hours. Plasma concentrations of free fatty acids and serum concentrations of total bilirubin, apparent unbound bilirubin, and albumin were measured at regular intervals. Effects of the three regimens on serum bilirubin measurements were determined. The regimen of fat infusion and rate of infusion seemed to have no effect on serum concentrations of total and apparent unbound bilirubin, although there was a trend towards greater variability in apparent unbound concentrations with the intermittent regimen.

Estimates of body water content in normally grown baboons during the first postnatal month.

Water contents of various body compartments were estimated within 9 h of birth in eight baboon neonates and at a mean of 29 days (27-32 days) in seven baboons. All animals were normally grown and delivered spontaneously at term. There was no difference in mean antipyrine space, corrected bromide space, intracellular water, interstitial water, and plasma and blood volumes observed on day 1 and day 29. Mean estimate of red cell volume was lower on day 29 than on day 1.

Effect of extracorporeal membrane oxygenation on body water content and distribution of baboon neonates.

Water contents of the various body compartments were estimated before and after a 7- to 10-h period of extracorporeal membrane oxygenation in five healthy baboon neonates. Total body water, extracellular water, and plasma volume were estimated simultaneously by antipyrine, bromide, and T-1824 dilution. Volumes of intracellular water, interstitial water, and blood and red cells were calculated from the experimental estimates. Mean preextracorporeal membrane oxygenation estimates of body water volume were in agreement with those previously reported in baboon neonates. During extracorporeal membrane oxygenation, no statistically significant changes occurred in the water content of the various body compartments. This absence of changes was contrasted to the changes demonstrated in human infants and adults undergoing intracardiac surgery with extracorporeal oxygenation and hypothermia and various hypotheses were put forward to explain the different changes observed.

Tolerance of fat emulsions in very-low-birthweight neonates. Monitoring of plasma lipid concentrations.

Tolerance to parenterally administered fat emulsions was studied in 45 normally grown neonates ranging from 820 to 1550 gm in birthweight, from 27 to 34 weeks in gestational age, and from 2 to 10 days postnatal age. Concentrations of total lipids, free glycerol, true triglycerides, free fatty acids, and cholesterol in plasma were studied over an 8-day period. The aim was to determine whether the concentrations of any one lipid fraction could be used to predict those of other fractions. With 650 pairs of data being correlated, the best correlation coefficients were obtained between total lipids and triglycerides (r = 0.67), total lipids and cholesterol (r = 0.63), free glycerol and free fatty acids (r = 0.55), total lipids and free fatty acids (r = 0.54), and triglycerides and free fatty acids (r = 0.50). Although all correlation coefficients were highly significant statistically (P less than 0.001), the very large standard errors precluded using any of these relationships to make clinical predictions. Problems and limitations of currently available techniques are discussed in order to provide a lead for further research.

Tolerance of fat emulsions in very low birthweight neonates: effect of birthweight on plasma lipid concentrations.

Plasma concentrations of various lipid fractions (total lipids, free glycerol, true triglycerides, free fatty acids, and cholesterol) were studied in 20 normally grown neonates ranging in birthweight from 820 to 1500 gm and in gestational age from 28 to 34 weeks. They were subdivided into three weight categories: 750 to 999, 1000 to 1249, and 1250 to 1500 gm. A lipid emulsion was infused at a constant rate over 24 hours, beginning with an hourly infusion rate of 0.04 gm/kg and increasing each day by 0.04 gm/kg up to a maximum of 0.16 gm/kg. Neonates who weighed less than 1000 gm had higher mean plasma concentrations of total lipids and free glycerol at hourly infusion rates of 0.08 and 0.16 and of triglycerides and free fatty acids at hourly infusion rate of 0.16 gm/kg than their heavier peers. These data suggest that extreme caution be used when administering parenteral fat emulsions to neonates who weigh less than 1000 gm and that we need to monitor plasma closely for signs of hyperlipemia.