Fluid and electrolyte metabolism in the newborn infant

Water, sodium and acid-base balance in premature infants: therapeutical aspects

One of the main targets of fluid therapy in premature infants is to avoid variations in osmolality, which mainly means providing a stable sodium, glucose, and acid-base balance. Water, sodium, and acid-base balance were measured in 20 infants appropriate-for-gestational age with a gestational age less than or equal to 34 weeks. The infants were randomly assigned to one of two treatment groups. Fluid intake was restricted and air humidity in the incubator was high in order to minimize insensible water loss. Sodium intake in Group 1 was 2 mmol/kg/day and consisted of sodium chloride. Sodium intake in Group 2 was 4 mmol/kg/day and consisted of both sodium chloride and acetate. Weight loss was appropriate in both groups. In the high sodium intake group there was a tendency towards a more stable plasma sodium concentration than in the low sodium intake group. The use of sodium acetate was efficient and practical as normal acid-base balance was maintained. The protocol with restricted fluid intake (1st day 50 ml/kg, 2nd day 70 ml/kg, 3rd day 90 ml/kg, and 4th day 110 ml/kg), high air humidity, a sodium supply of 3 to 4 mmol/kg/day, and a slow correction of metabolic acidosis with sodium acetate, yields suitable guidelines in planning fluid and electrolyte therapy in premature infants less than or equal to 34 weeks' gestation.

Plasma and urine osmolality in full-term and pre-term infants

The purpose of the present study was to determine the normal relationship of urine and plasma osmolality in pre-term and full-term infants. Twenty-nine full-term and 35 pre-term babies were studied during the first week of life. Random simultaneous urine and plasma samples were measured for osmolality. Statistical analysis defined the normal relationship of plasma to urine osmolality. This suggests an osmotic threshold of 282 mOsm/kg and 291 mOsm/kg for full-term and pre-term babies, respectively. These values are different from the 285-290 mOsm/kg of adolescents and adults. The nomograms provided may serve as a useful aid in the bedside diagnosis of dysfunctional secretion of vasopressin.

Central control of vasopressin release and thirst

The effects of changes in the composition and/or the volume of the extracellular fluid on central receptors involved in the regulation of water balance are discussed. A review of results obtained in adults is given, followed by a discussion of possible roles for vasopressin during the neonatal period.

The effect of enteric galactose on neonatal canine carbohydrate metabolism

Newborn pups were assigned to a fasting group or to a group receiving intravenous glucose alimentation. Glucose turnover was determined during steady state equilibration of simultaneously infused [6-3H] glucose. Thereafter, pups from each group received 0.625 g/Kg of either oral [U-14C] galactose or [U-14C] glucose. In fasted or intravenously alimented pups enteric glucose resulted in a rapid and sustained elevation of blood glucose concentrations. Systemic appearance of carbon-14 label from enteric glucose increased rapidly as did the enrichment of blood [14C] glucose specific activity. In those pups given enteric galactose, blood glucose values were equivalent to that in the glucose fed groups, however carbon-14 appearing in blood glucose and blood glucose specific activity was significantly lower. The peak values for rates of appearance and disappearance of systemic glucose were significantly lower in pups fed galactose than among pups fed glucose. Glucose clearance was also significantly lower in these pups despite equivalent plasma insulin responses. Among fasting pups hepatic glycogen content was significantly higher in those given either oral glucose or galactose when compared to a completely starved control group. In contrast, among alimented pups galactose administration significantly enhanced hepatic glycogen content compared to those fed glucose. Similarly, enteric substrate label incorporation into hepatic glycogen was enhanced in both groups given oral labeled galactose. In addition, hepatic glycogen synthase (glucose-6-phosphate independent) activity was increased only among alimented pups fed galactose when compared to completely fasted pups. In conclusion these data suggest that following gastrointestinal galactose administration, hepatic carbohydrate uptake is augmented while glycogen synthesis may be enhanced. Augmented glycogen synthesis following galactose administration may reflect alterations in hepatic glycogen synthase activity or enhanced hepatic carbohydrate uptake.