Metabolic alkalosis may be caused by a loss of hydrogen ions or a gain of bicarbonate. It is due mainly to problems of the kidney or gastrointestinal tract

Causes

• vomiting / aspiration
  • (e.g. peptic ulcer leading to pyloric stenos, nasogastric suction)
  • vomiting may also lead to hypokalaemia
• diuretics
• liquorice, carbenoxolone
• hypokalaemia
• primary hyperaldosteronism
• Cushing's syndrome
• Bartter's syndrome

Mechanism of metabolic alkalosis

• activation of renin-angiotensin II-aldosterone (RAA) system is a key factor
• aldosterone causes reabsorption of Na in exchange for H+ in the distal convoluted tubule
• ECF depletion (vomiting, diuretics) → Na+ and Cl- loss → activation of RAA system → raised aldosterone levels
• in hypokalaemia, K+ shift from cells → ECF, alkalosis is caused by shift of H+ into cells to maintain neutrality