What is the rationale behind hypotonic maintenance fluids?
Maintenance solutions contain less sodium and more potassium than do replacement fluids. Many maintenance solutions contain approximately 50 mEq sodium per liter. Consider a 10 kg dog with 6 L of total body water. Four liters is intracellular fluid with a sodium concentration of 10 mEq/L (total of 40 mEq) and 2 liters is extracellular fluid with a sodium concentration of 140 mEq/L (total of 280 mEq). Thus, the average sodium concentration of the total body water is approximately 320 mEq divided by 6 liters or 53 mEq/L. Thus, maintenance solutions provide a sodium concentration that approximates the average sodium concentration of total body water. This same approach however cannot be applied to potassium because excessively rapid intravenous administration of solutions containing large amounts of potassium can be lethal (see question above—the maximum safe intravenous infusion rate for potassium is 0.5 mEq/kg/hr). Thus, most maintenance solutions do not contain more than 15 mEq/L of po
