Why must nitric oxide be removed from the respiratory circuit?

• A. To prevent formation of carbon monoxide
• B. To avoid toxic effects from nitrogen dioxide formation
• C. To increase oxygen delivery
• D. To reduce nitric oxide half-life

Answer: (B)

Nitric oxide must be removed because it can react with oxygen in the airway to form nitrogen dioxide (NO2), a toxic gas. NO2 irritates and damages the lungs, causing inflammation, edema, and respiratory injury. To prevent exposure to this harmful byproduct, the exhaust from the respiratory circuit is treated to remove NO/NO2 before it’s released into the room or environment. The other options don’t fit: nitric oxide doesn’t form carbon monoxide in this context, removing it wouldn’t inherently increase oxygen delivery, and NO’s half-life is already very short—the concern is preventing NO2 formation, not just shortening NO.