24% of candidates passed this question.

Nitric Oxide (NO) is an inorganic colourless and odourless gas presented in cylinders containing 100/800 ppm of NO and nitrogen. Many candidates mentioned oxygen instead of nitrogen. The exposure of NO to oxygen is minimized to reduce formation of nitrogen dioxide and free radicals. Hence it is administered in inspiratory limb close to the endotracheal tube. Many candidates did not mention the contraindications/caution for NO use. Candidates generally did well in mentioning the impact on improving V/Q mismatch by promoting vasodilatation only in the ventilated alveoli and reducing RV afterload. Many candidates did not mention the extra cardio-respiratory effects. The expected adverse effects of NO were nitrogen dioxide related pulmonary toxicity, methemoglobinemia and rebound pulmonary hypertension on abrupt cessation. Pharmacokinetics of NO carried a significant proportion of marks. It was expected that the answers would involve mention of location of delivery of NO in inspiratory limb and reason behind it, the high lipid solubility and diffusion, the dose (5-20ppm), very short half-life of < 5 seconds and combination with oxyhemoglobin to produce methaemoglobin and nitrate. The main metabolite is nitrate which is excreted in urine.