Persistent vomiting leads to loss of large amount of gastric fluid. Gastric fluid consists of large amount of HCL along with potassium Thus the metabolic abnormality associated with repeated vomiting is metabolic alkalosis in combination with hypochloretnia and hypokaletnia. In the early stages the kidneys are able to compensate by reabsorbing hydrogen and chloride ions in exchange for sodium potassium and bicarbonate, however as the body stores of sodium and especially potassium becomes depleted these ions are selectively retained while hydrogen is excreted in the urine, causing the paradoxical aciduria. The excretion of hydrogen in the urine aggravates the alkalotic stage.