This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Stomach & Duodenum, Subject name: Surgery
Excessive vomiting with gastric outlet obstruction secondary to pyloric stenosis leads to - 
Select and explain. 
A. Hypokalemic hypochloremic metabolic alkalosis, B. Hypokalemic hyperchloremic metabolic acidosis, C. Hyperkalemic hyperchloremic metabolic alkalosis, D. Hyperkalemic hypochloremic metabolic acidosis
A: Hypokalemic hypochloremic metabolic alkalosis
Answer: A: Hypokalemic hypochloremic metabolic alkalosis 
Explanation: Ans. is 'a' i.e., Hypokalemic hypochloremic metabolic alkalosis Metabolic consequences of persistent vomiting in case of pyloric stenosis:* The metabolic consequences of benign pyloric stenosis are unique.* The vomiting of hydrochloric acid results in hypochloraemic alkalosis.* Initially, the sodium and potassium may be relatively normal. However, as dehydration progresses, more profound metabolic abnormalities arise, partly related to renal dysfunction.* Initially, the urine has a low chloride and high bicarbonate content, reflecting the primary metabolic abnormality. This bicarbonate is excreted along with sodium, and so with time the patient becomes progressively* Hyponatraemic and more profoundly dehydrated.* Because of the dehydration, a phase of sodium retention follows and potassium and hydrogen are excreted in preference.* This results in the urine becoming paradoxically acidic and hypokalaemia ensues. This finally culminates into hypokalemic hypochloremic metabolic alkalosis.* Alkalosis leads to a lowering in the circulating ionised calcium, and tetany can occur.