Dehydration and oral or intravenous rehydration

Overview & Definition

A child who has been vomiting and passing watery stools for two days, who is now listless with sunken eyes and a dry mouth, is the everyday face of dehydration and the most common paediatric fluid emergency. The defining problem is a net loss of body water and electrolytes that outruns intake, so the extracellular volume contracts and the circulating volume falls until the tissues are underperfused. Most episodes follow acute gastroenteritis, and most are mild, but the small proportion that progress to severe dehydration carry a real risk of shock, electrolyte crisis, and cerebral oedema. [11]

The degree of dehydration is expressed most usefully as a percentage of body weight lost, because a recent weight is the single most reliable measure of the water deficit. A loss below 5 percent of body weight is mild and usually clinically inapparent, a loss of 5 to 10 percent produces the recognisable signs of moderate dehydration, and a loss above 10 percent is severe and accompanied by shock and a threatened circulation. The clinical dehydration scale converts these weight bands into a reproducible bedside score, so the clinician can grade severity without waiting for a weight or a blood test. [4]

The treatment is simple in concept and exact in execution, which is the whole point of the topic for an examiner. Mild and moderate dehydration are managed with oral rehydration therapy using reduced-osmolarity oral rehydration solution, which works as well as intravenous fluid and avoids the cannula and the admission. Severe dehydration and shock need intravenous isotonic crystalloid in a staged protocol, and the dysnatraemic child needs that fluid given slowly, because the brain defends its volume and a rapid correction causes cerebral oedema. [7]

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