The mainstay of management of diarrhoeal disease is the assessment of dehydration (Figure 50.1) and the appropriate replacement of fluid and electrolytes.^[29] Although diarrhoeal disease can produce dehydration at any age, its impact is greatest in those under 5 years old. This is because, as a result of their relatively greater surface area and thus greater fluid loss through skin, infants require 2.5 times more water per kilogram body weight than older individuals. Fluid and electrolyte loss is also greatly exacerbated by vomiting. Both the initial degree of dehydration and the response to rehydration therapy should be monitored clinically (Table 50.6).

Originally, rehydration was exclusively intravenous. This resulted in a tremendous drop in fatality rates – for example, in cholera, from 40% to less than 1% when properly administered. A major advance was made when an effective oral rehydration regimen was devised.