A young child, 3 year old, has presented with vomiting for 3 days. Examination: mild to moderate dehydration. What is his ABG (arterial blood gas) profile likely to show?

The key is D. pH high, PCO2 high. [Prolonged vomiting causes loss of H+, Cl- and Na+. There is also hypokalemia. There occur metabolic alkalosis. Compensation for metabolic alkalosis occurs mainly in the lungs, which retain carbon dioxide (CO2) through slower breathing, or hypoventilation (respiratory compensation) leading to high PCO2].