contraction alkalosis
Summary
Contraction alkalosis is metabolic alkalosis caused by disproportionate loss of chloride and volume relative to bicarbonate, often from vomiting, NG suction, or diuretic use. The kidneys retain bicarbonate to restore volume, perpetuating alkalosis.
Detail
Loss of HCl directly increases plasma bicarbonate, and volume contraction activates RAAS. Aldosterone increases distal Na+ reabsorption with HCO3- and H+ secretion, worsening alkalosis. Loop and thiazide diuretics cause contraction alkalosis by inducing volume depletion and Cl- losses. Characterized by low urine chloride (<10 mEq/L, 'chloride-responsive'). Treatment requires volume repletion with normal saline and correction of hypokalemia.
Sources
- First Aid for the USMLE Step 1
- Pathoma
- Harrison's Principles of Internal Medicine
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