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.

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.

PAH, p-aminohippurateNumerous studies of perinatal physiology, metabolism, nutrition, and pathologic conditions require estimation of the fluid content of various body compartments. As direct volumetric determinations are not possible in vivo, less direct methods must be relied upon to obtain an acceptable estimate. The most commonly used techniques involve a principle developed by Fick. Fick's principle states that the fluid content (V) of a given space may be calculated following the administration of a dye or chemical into that space if the exact amount (Q) of substance injected and its concentration (C) in the fluid of the space are Rece~ved August 15, 1988; accepted November 22, 1988 known, or V = Q/C. The dye or chemical must have five main properties: It must I ) be harmless to the organism; 2) be easily measurable; 3) diffuse evenly and within a predictable period of time throughout its vol of distribution; 4) have no effect on fluxes of fluids across membranes; and 5 ) neither be metabolized nor leave the space for which the vol is being measured for the duration of the study. This last requirement is seldom met. If, however, the decrease in dye concentration with time follows a straight line, extrapolation of that line to time 0 (y-intercept or Co) still allows a vol determination to be made, or V = Q/Co. In that case, the rate at which the substance escapes from its vol of distribution, be it by metabolism or excretion, may be also calculated (slope of the concentration versus time line).In cases where all four criteria are met, the marker diffuses as soon as it is administered to reach an even concentration throughout its vol of distribution. In cases where the fourth criterion is not met, two phenomena occur simultaneously as soon as the marker is administered. First, the marker diffuses to reach an even concentration throughout its vol of distribution; second it is being cleared from its assigned space. To interpret the data correctly, it is important to determine at what point in time equilibration is complete and the behavior of the marker concentration thereafter, i.e. the kinetics of the marker. Yet kinetic data have often been disregarded or remained buried in the investigators' laboratory data books and are scarce in the relevant literature. Also, in human perinatal medicine, there are ethical and practical limitations on the number and vol of body fluid samples that may be obtained. In this report, we have made use of the baboon (Papio cynocephalus), whose fetoplacentouterine unit and neonatal physiology and metabolism are very similar to those of Homo sapiens, to determine the kinetics of six markers: PAH (amniotic fluid vol), inulin (amniotic fluid vol), antipyrine (total body water), H2'" (total body water), bromide (extracellular water) and T-1824 (plasma vol). From these kinetics, precise recommendations may be made regarding optimal time and method of amniotic fluid or blood sampling. MATERIALS A N D METHODSPAIf and inulin dilution. The kinetics of PAH and inulin dilution in amniotic f...

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.

METHODSFive healthy baboon (Papio cynocephalus) neonates (two male and three female) were studied. Postnatal ages at the time of study ranged from 17 to 28 days. Body weights, measured to the nearest gram, ranged from 820 to 1478 g. Each animal was anesthetized with 10 mg/kg ketamine hydrochloride and 0.05 mg/kg diazepam. These doses were repeated as needed for sedation until muscle relaxants were instituted. Thereafter, both drugs were administered every 20 min for three doses, every 30 min for two doses and then hourly. A neonatal monitor was used to measure rectal temperature, heart rate, and respiratory rate. Each animal was intubated using a 3.0-mm internal diameter endotracheal tube which fit snugly through the vocal cords. Pancuronium bromide 0.2 mg/kg was administered and the ventilator was adjusted as required. The right femoral artery was catheterized using a 3.5 F umbilical artery catheter. This line was used to monitor the animal's blood pressure and arterial blood gasses. The left femoral artery was also catheterized with the largest allowable catheter (5 or 6 F). This catheter was used to return oxygenated blood to the distal aorta. A Bourns BP 200 ventilator was adjusted to provide an arterial pcoz of 35 to 45 Torr and an arterial pOz greater than or equal to 55 Torr.Through an incision medial to the belly of the right sternocleidomastoid muscle, the right internal jugular vein and common carotid artery were identified. Both vessels were isolated and prepared for cannulation. A 3.5 or 5 F umbilical artery catheter was passed distally up the internal jugular vein to the base of the skull and the vein was ligated proximally. Through the carotid artery, the largest allowable catheter (5 or 6 F) was passed to the level of the aortic arch. This catheter was used to return oxygenated blood to the proximal aorta. A midline sternotomy was performed and the pericardium was reflected and secured to the sternal edges. The ductus arteriosus was identified and ligated, and umbilical tapes were passed around the root of the aorta and the pulmonary artery and out through a cut segment of red rubber catheter to serve as Romel snares. A 14 F venous cannula was introduced into the right atrium through an incision in the right atrial appendage, and the cannula was secured in place. The positions of all catheters and of the endotracheal tube were verified radiographically.The ECMO circuit was assembled and primed as described previously by Bartlett (4). Blood samples (125 ml) were collected from each of four healthy adult baboons and pooled 24 to 72 h prior to each experiment. The blood was centrifuged to separate the plasma from the red cells within a few hours of drawing. The red cells were then stored at 4 0 C until the pump was primed just 381 Abbreviations ECMO, extracorporeal membrane oxygenation CBS, corrected bromide space ABSTRACT. 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 bo...