What is the minimum humidity value delivered by a humidifier in this context?

• A. 10 mg H2O/L
• B. 20 mg H2O/L
• C. 30 mg H2O/L
• D. 40 mg H2O/L

Answer: (C)

Maintaining adequate humidity in the inspired gas is essential to protect the airway and support mucociliary function. Humidity is measured as absolute humidity, the amount of water (in mg) per liter of gas. The minimum acceptable delivered value on many ventilator humidification guidelines is 30 mg H2O per liter. Providing at least this level helps keep the airway mucosa hydrated, keeps secretions less viscous, and supports ciliary clearance; values much lower than this (10 or 20 mg/L) increase the risk of drying and mucus plugging, while 40 mg/L would be more than the minimum needed. Therefore, 30 mg H2O/L is the correct minimum.