Water Balance in Infants During Water Deprivation

Introduction Loss of body water occurs normally through the skin, respiratory passages, intestine, and kidney. Abnormal losses of hypotonic fluid may result from diarrhea and vomiting, sweating, and hyperpnea. Under these circumstances, hypertonicity of residual body fluids is partially counteracted by renal conservation of water relative to solute through the elaboration of hypertonic urine. Inadequacy of this mechanism contributes to decreased volume and increased osmolality of body water. In considering water conservation, Gamble 1 defined the minimal renal water requirement as the minimum volume of urine containing the measured solute excreted (millimols per 24 hr.) at the maximally achievable concentration (millimols per milliliter). Data on the rates of solute excretion in premature and full-term infants fed modified and unmodified whole cow's milk formulas as well as commercially available diets of varying protein content available. 2-4 Urinary osmolality during water deprivation was measured by Pratt 5 in 1-month-old infants and by