Causes

• Loss of total body fluid, Na + , Cl + , K+ usually due to:

• large nasogastric aspirates, vomiting

• Secondary hyperaldosteronism with potassium depletion

• Use of haemofiltration replacement fluid containing excess buffer (e.g. lactate)

• Renal compensation for chronic hypercapnia. This can develop within 1-2 weeks. Although more apparent when the patient hyperventilates, or is hyperventilated to normocapnia, an overcompensated metabolic alkalosis can occasionally be seen in the chronic state (i.e. a raised pH in an otherwise stable long term hypercapnic patient)

• Excess administration of bicarbonate

• Excess administration of citrate (large blood transfusion)

• Drugs, including laxative abuse, corticosteroids

• Rarely, Cushing's, Conn's, Bartter's syndrome

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