Which mechanism explains the metabolic alkalosis observed with chronic diuretic therapy for ascites and edema?

Which mechanism explains the metabolic alkalosis observed with chronic diuretic therapy for ascites and edema?

• A. Loss of bicarbonate-poor, chloride-rich extracellular fluid causing contraction and higher bicarbonate concentration
• B. Increased bicarbonate production by the kidneys
• C. Hyperventilation leading to decreased CO2
• D. Ingestion of bicarbonate-rich antacids

Answer: (A)

Contraction alkalosis from diuretic-induced volume loss is the key mechanism. Chronic diuretic therapy reduces extracellular fluid, and the fluid lost is chloride-rich and bicarbonate-poor. As the body attempts to restore volume, the kidneys conserve sodium, and aldosterone-driven processes increase hydrogen ion loss and bicarbonate reabsorption. chloride depletion impairs bicarbonate excretion in the distal nephron, so plasma bicarbonate rises, producing metabolic alkalosis. The other scenarios—such as new bicarbonate production, hyperventilation-induced CO2 loss, or external bicarbonate ingestion—don’t explain the diuretic-associated alkalosis in this setting.

Contraction alkalosis from diuretic-induced volume loss is the key mechanism. Chronic diuretic therapy reduces extracellular fluid, and the fluid lost is chloride-rich and bicarbonate-poor. As the body attempts to restore volume, the kidneys conserve sodium, and aldosterone-driven processes increase hydrogen ion loss and bicarbonate reabsorption. chloride depletion impairs bicarbonate excretion in the distal nephron, so plasma bicarbonate rises, producing metabolic alkalosis. The other scenarios—such as new bicarbonate production, hyperventilation-induced CO2 loss, or external bicarbonate ingestion—don’t explain the diuretic-associated alkalosis in this setting.