Which is a common side effect of inhaled nitric oxide (NO) therapy?

• A. Formation of free-oxygen radicals
• B. Improved oxygenation
• C. Production of nitrogen dioxide (NO2)
• D. No adverse effects

Answer: (C)

Inhaled nitric oxide helps by dilating the pulmonary vessels to improve oxygenation, but a common adverse effect comes from NO reacting with oxygen in the airways to form nitrogen dioxide. NO2 is a toxic oxidant that can irritate and injure the airways if not monitored, so its production is the classic side effect clinicians watch for during NO therapy. Improved oxygenation is a therapeutic effect, not a side effect, and while there are other potential concerns at higher doses (like methemoglobinemia), NO2 formation remains the most recognized common adverse effect. Saying there are no adverse effects isn’t accurate because NO2 production can cause irritation and lung injury with inappropriate dosing or monitoring.