Monitoring an infant on inhaled nitric oxide (iNO) therapy includes measurement of which parameter?

• A. Liver function values
• B. Methemoglobin levels
• C. Ventilation-perfusion disturbances (V/Q)
• D. Blood pressure

Answer: (B)

Inhaled nitric oxide can oxidize iron in hemoglobin to methemoglobin, which cannot effectively carry oxygen. Therefore, methemoglobin level is the parameter to monitor. Measuring it with co-oximetry on blood samples allows early detection of methemoglobinemia; if levels rise, iNO can be adjusted or stopped to prevent worsening hypoxemia. Baseline levels before starting therapy and periodic monitoring during treatment are standard. While other parameters like liver function, ventilation-perfusion status, or blood pressure are relevant to overall care, methemoglobin monitoring specifically tracks the main safety risk of iNO therapy.