ASSESSING FLUID AND ELECTROLYTE STATUS IN THE NEWBORN

Fluid and electrolyte assessment during the first week of life is comp licated by rapid changes in fluid and electrolyte balance during the t ransition from fetal to neonatal life and by the newborn's small size. A physiologic decrease in extracellular water volume, as well as a tr ansient increase in serum potassium and transient decreases in plasma glucose and total plasma ionized calcium concentrations must be taken into account. In general, the more immature the newborn, the greater t he changes that can be expected. The use of plasma creatinine as an in dicator of glomerular filtration rate is limited because it is a funct ion of maternal renal function at birth and because of non-steady-stat e conditions in the immediate postnatal period. Guidelines for monitor ing schedules are provided on the basis of these physiologic considera tions and the author's experience. Method of blood sampling and time t o separation of serum are important considerations in interpreting res ults. Minimization of sample volume is critical to minimize blood tran sfusion requirements. Clinicians should be aware of the analytical err or associated with these measurements in their own institutions. Refer ence ranges are provided.