Plasma osmolality and protein intake in preterm infants.

Davies, D. P. (1973). Archives of Disease in Childhood, 48, 575. Plasma osmolality and protein intake in preterm infants. Plasma osmolality was measured in 53 preterm, low birthweight infants on 3 days (days 7, 14, and 28) during the first month of life. The aim of the study was to compare the plasma osmolality of infants fed expressed human breast milk with that of infants fed two proprietary cow's milk formulae of higher protein content. The mean plasma osmolality in 15 infants fed Ostermilk No. 1 (group B), with protein contributing 15X4% of the total calorie intake (2.7 g/100 ml), did not differ from that of 17 infants on human milk (group A) in which protein made up only 5 *9% of the total calorie content (1 1 g/100 ml). 21 infants fed Ostermilk C.20 (group C), with 21 * 1% ofthe calorie content provided by protein (3 *7 g/100 ml), had significantly higher mean values than group A infants; the highest mean plasma osmolality occurred with a daily protein intake of 8 5 g/kg. The number of individual observations > 300 mOsm/l. in groups A, B, and C were 4, 4, and 16, accounting respectively for 9 * 1, 10 * 8, and 32 * 6% of the total number of observations in each group. The higher plasma osmolality in group C infants was not accompanied by significant weight gain or clinical oedema. It is suggested that a milk formula with protein contributing more than 20% ofthe total calorie intake or a daily protein intake greater than 8 0 g/kg considerably stresses the capacity ofthe immature kidney to maintain plasma osmolality within normal limits, and should, therefore, be used with caution if hyperosmolar states are to be avoided.