A humidifier used with a mechanical ventilator should deliver a minimum of how much humidity?

• A. 20 mg H2O/L
• B. 30 mg H2O/L at 31-35°C
• C. 40 mg H2O/L
• D. 50 mg H2O/L

Answer: (B)

The key idea is that ventilator humidification should deliver a minimum amount of water vapor per liter of gas, known as absolute humidity, to protect the airway surfaces. The standard target is at least 30 mg of H2O per liter, measured with the gas at about 31–35°C. This level provides enough moisture to keep mucus thin and promote effective mucociliary function, reducing airway drying and secretion viscosity without causing excessive condensation in the circuit. While gas at body temperature can hold more water (closer to 44 mg/L at 37°C), aiming for around 30 mg/L at 31–35°C balances adequate humidification with the practical risks of condensation and circuit pooling. So delivering about 30 mg/L at 31–35°C is the recommended minimum.