Rehydration

Rehydration is the correction of dehydration by replacing water and, when necessary, electrolytes that have been lost from the body. Dehydration develops when body-water losses exceed replacement and can occur with varying degrees of electrolyte loss. Rehydration therefore aims to restore body-fluid volume and composition toward normal .^1,2

Fluid for rehydration can be taken through the gastrointestinal tract or, when clinically necessary, administered directly into the circulation. Oral rehydration is particularly effective for fluid losses caused by diarrhea because the small intestine can continue to absorb sodium and glucose together during many diarrheal illnesses. Water is absorbed along with these solutes, allowing a properly formulated oral rehydration solution to replace both water and electrolytes .^1,2

Oral rehydration solutions (ORS) contain water together with specific amounts of glucose and electrolytes. Glucose is included not primarily as an energy source but because its coupled absorption with sodium promotes intestinal sodium and water uptake. The electrolytes in the solution also help replace ions lost from the body. This makes ORS different from simply drinking water when substantial electrolyte losses have occurred .^1,2

Rehydration and hydration are related but not identical concepts. Hydration describes body-water status or the maintenance of adequate body water, whereas rehydration specifically refers to restoring fluid after dehydration has developed. The amount and composition of fluid required for rehydration therefore depend on the nature and extent of the preceding fluid and electrolyte losses .¹