These occur because of the loss of sodium, bicarbonate and potassium associated with watery stools. The electrolyte status of patientswith severe diarrhoeal dehydration, circulatory disturbances or metabolic acidosis should be ascertained.
• Metabolic acidosis is almost always present if the patient has significant dehydration, and is identified by more rapid deep respirations with a clear chest on auscultation. Unless metabolic acidosis is severe, sodium bicarbonate is usually not required, as rehydration allows for correction. Rehydration fluid contains alkali in the form of citrate or bicarbonate. A wide anion gap may suggest the possibility of severe ketosis, salicylate intoxication or lactic acidosis.
• Large amounts of potassium are lost in diarrhoeal stools. Metabolic acidosis is associated with further urinary potassium loss. In acidosis, a shift of intracellular potassium to the extracellular compartment results in a spurious elevation of the serum level, despite intracellular potassium loss. All children suffering from severe diarrhoea should receive oral potassium chloride: 125 mg 8-hourly if under 1 year of age, and 250 mg 8-hourly if over 1 year of age, until dehydration and acidosis are corrected.
• Sodium disturbances occur frequently. Sodium content of the stool water varies from plasma-like in secretory diarrhoea (such as cholera), to very low in pure osmotic diarrhoea. In general, serum sodium is inversely related to the state of the intracellular water compartment, i.e. raised serum sodium reflects intracellular dehydration. Hypo- and hypernatraemia management should follow recommended guidelines; however, where ORT is possible, the process of rehydration usually allows metabolic homeostasis to be re-established.
• Blood glucose disturbances occur in severely ill young children as a result of glycogen depletion with lack of intake, or in association with the stress response of dehydration. Blood glucose estimation should be performed by finger-prick test in all dehydrated children.
Dehydrated or malnourished children are likely to have a metabolic disturbance.