Humidification during mechanical ventilation is necessary to prevent inspissation of airway secretions, hypothermia, and atelectasis. This can be accomplished using either a heat and moisture exchanger (HME) or a heated humidifier.

A humidification device should provide a minimum of 30 mg H2O/L of delivered gas at 33 + 2C. HME's are passive humidification systems that retain heat and moisture from the patient's exhaled gas via a hygroscopic filter. Heated humidifiers (or active humidification systems) operate actively to increase the heat and water vapor content of the inspired gas.