James W. Kendig

Changes in Pulmonary Mechanics after the Administration of Surfactant to Infants with Respiratory Distress Syndrome

We assessed pulmonary mechanics in 35 premature infants with respiratory distress syndrome just before and one hour after the administration of 90 mg of surfactant to each infant. Transpulmonary pressure was measured between the airway opening and an esophageal balloon with use of a differential transducer, and flow rates were measured by a pneumotachometer. Values for pulmonary mechanics were then calculated by microcomputer processing. The administration of surfactant produced a large decrease (56 percent) in the mean (+/- SEM) ratio of alveolar to arterial oxygen, from 7.1 +/- 0.5 to 3.1 +/- 0.2 (P less than 0.0001)--a change that indicates improvement in gas exchange. Associated changes in pulmonary mechanics were not demonstrable when 10 of the infants were studied during continuous mechanical ventilation. However, in the 25 infants examined during spontaneous breathing with continuous positive airway pressures (identical airway pressures before and after treatment), large and consistent improvements in pulmonary mechanics were found after the administration of surfactant. Tidal volume increased by 32 percent (P less than 0.03), minute ventilation by 38 percent (P less than 0.02), dynamic compliance by 29 percent (P less than 0.004), and inspiratory flow rates by 54 percent (P less than 0.01). We conclude that significant improvement in pulmonary mechanics results from surfactant-replacement therapy for respiratory distress syndrome, but that these mechanical changes are apparent only during spontaneous respiration and can be masked if measurements are made during mechanical ventilation.

Feeding premature infants while low umbilical artery catheters are in place: A prospective, randomized trial

OBJECTIVE The objective of this prospective, randomized clinical trial was to test the hypothesis that there is no difference in the frequency of feeding problems and necrotizing enterocolitis between a group of premature infants who received early enteral feedings while low umbilical artery catheters (LUACs) were in place, and a late group who were not fed until 24 hours after removal of LUACs. PATIENTS AND METHODS Twenty-nine premature infants (born at 28.5 +/- 3.0 SD weeks of gestational age) who were in stable condition received early enteral feedings at a median of 2 days while a LUAC was in place; 31 infants (born at 28.6 +/- 2.7 SD weeks of gestational age) received late enteral feedings at a median of 5 days of age, 24 hours after the removal of the LUAC. Feeding complications and interventions and nutritional characteristics were recorded prospectively. RESULTS There were no differences in the baseline perinatal characteristics of the two groups. The incidence of gastric residua and the incidence of abdominal distention were the same in both groups. The early feeding group had significantly fewer percutaneous central venous catheters, evaluations for sepsis, and episodes of receiving nothing by mouth while a gastric suction tube was in place. Infants in the early group received parenteral alimentation-lipid emulsion infusions for a median of 13 days versus 30 days for the late-fed group (p = 0.0028 by Wilcoxon test). There were two cases of necrotizing enterocolitis in the early group versus four cases in the late group. CONCLUSIONS Premature infants in stable condition who receive enteral feedings while LUACs are in place do not have an increased incidence of feeding problems compared with infants who do not receive enteral feedings until 24 hours after removal of LUACs.

Concentration-dependent, temperature-dependent non-Newtonian viscosity of lung surfactant dispersions.

The bulk shear viscosities of aqueous dispersions of lavaged calf lung surfactant (LS) and its chloroform:methanol extract (CLSE) were measured as a function of concentration, shear rate and temperature. At 10-mg phospholipid per milliliter, dispersions of LS and vortexed CLSE in 0.15 M NaCl (saline) had low viscosities near 1 cp over a range of shear rates from 225 to 1125 s(-1). Lung surfactant viscosity increased with phospholipid concentration and became strongly non-Newtonian with higher values at low shear rates. At 37 degrees C and 40 mg/ml, LS and vortexed CLSE in saline had viscosities of 38 and 34 cp (77 s(-1)) and 12 and 7 cp (770 s(-1)), respectively. Viscosity values for LS and CLSE were dependent on temperature and, at fixed shear, were lower at 23 degrees C than at 37 or 10 degrees C. Hysteresis was also present in viscosity measurements depending on whether shear rate was successively increased or decreased during study. Addition of 5 mM Ca(2+) at 37 degrees C markedly reduced CLSE viscosity at all shear rates and decreased LS viscosity at low shear rates. Dispersion by sonication rather than vortexing increased the viscosity of CLSE at fixed shear, while synthetic phospholipids dispersed by either method had low, relatively Newtonian viscosities. The complex viscous behavior of dispersions of LS and CLSE in saline results from their heterogeneous aggregated microstructure of phospholipids and apoproteins. Viscosity is influenced not only by the aggregate surface area under shear, but also by phospholipid-apoprotein interactions and aggregate structure/deformability. Similar complexities likely affect the viscosities of biologically-derived exogenous surfactant preparations administered to patients in clinical surfactant therapy.

Effect of Dexamethasone Therapy on Serum Vitamin E Concentrations in Premature Infants with Bronchopulmonary Dysplasia

OBJECTIVE: To investigate the effect of dexamethasone therapy on serum vitamin E concentrations in premature infants with bronchopulmonary dysplasia.STUDY DESIGN: A total of 10, 24 to 29 weeks’ gestational age, infants enrolled in a prospective study designed to evaluate the effect of dexamethasone on lipid intolerance were eligible for the study. Eight of these 10 infants had serum vitamin E concentrations measured simultaneously with serum triglyceride concentrations before the start of dexamethasone therapy (baseline) and within 5 days of the initiation of dexamethasone therapy. Charts were reviewed for vitamin E intake at baseline and on dexamethasone therapy for each of these eight infants.RESULTS: All eight infants had physiological serum vitamin E concentrations (1 to 3 mg/dl) at baseline, while six of eight infants had pharmacological serum vitamin E concentrations (≥3 mg/dl) on dexamethasone therapy. All infants with an increase in serum vitamin E concentration also had a simultaneous increase in serum triglyceride concentrations with a significant correlation between vitamin E and triglyceride concentrations (Spearmans ρ=0.92). There was a significant difference in mean serum vitamin E concentration between baseline and post-dexamethasone therapy (P=0.01, Wilcoxons signed-rank test). There was no significant difference in vitamin E intake between baseline and post-dexamethasone therapy.CONCLUSION: Dexamethasone therapy in premature infants induces significant increase in serum vitamin E concentrations to pharmacological levels independent of vitamin E intake.

SURFACTANT PROPHYLAXIS AS IMMEDIATE BOLUS (IB) VERSUS POST-VENTILATORY ALIQUOTS (PVA): A MULTICENTER RANDOMIZED TRIAL. † 1311

SURFACTANT PROPHYLAXIS AS IMMEDIATE BOLUS (IB) VERSUS POST-VENTILATORY ALIQUOTS (PVA): A MULTICENTER RANDOMIZED TRIAL. † 1311

Epidemiology of Neonatal Necrotizing Enterocolitis in the Post-Surfactant Era:A Population-Based Study

Epidemiology of Neonatal Necrotizing Enterocolitis in the Post-Surfactant Era:A Population-Based Study