Treatment of Dehydration in Infancy
Laurence Finberg MD1
1 Montefiore Hospital and Medical Center, Bronx, New York
NORMAL CHEMICAL ANATOMY AND PHYSIOLOGY
Before discussing dehydration it is worthwhile to review the normal features of an infant with respect to content and distribution of water and mineral. Approximately 70% of the lean body mass is water. The distribution of this water is shown in Fig 1. The plasma volume owes its integrity to its protein content, which is a relatively impermeable species of molecule. The extracellular fluid composition differs strikingly from the intracellular fluid despite the movement of most ions across cell membranes because of an active transport system (Na+, K+, ATPase) in the membrane that extrudes sodium. The compositional differences are diagrammed in Fig 2.
The second consideration necessary to handle any problem is that of obligatory water requirements to replace losses. Table 1 gives the relationship between caloric expenditure and water loss with the basal state as the point of reference. For ordinary clinical circumstances requirements are about 1
times basal state. Electrolyte requirements have a wide range. Practical considerations make it necessary to provide solute in an intravenous solution, when one is needed, to prevent hemolysis. All conditions may be met by allowing 2 to 3 mEq/kg/day of both sodium and potassium. Chloride and bicarbonate (or other base) ions for the healthy infant awaiting surgery, for example, should be divided about 3:1.
