HMEs

Heat and moisture exchangers (HMEs) are devices used in respiratory care to conserve heat and moisture from the patient’s exhaled breath and deliver it back to the inspired gas. They are commonly placed in ventilator circuits between the endotracheal or tracheostomy tube and the breathing apparatus, helping to maintain mucosal integrity and reduce drying of the airway.

HMEs work by capturing water vapor and heat from expired air using hygroscopic or porous materials and releasing it during inhalation. There are passive HMEs, which rely on the energy and moisture of exhaled air, and active HMEs, which include an external heating element to provide additional humidification. The principle is to approximate natural airway conditioning without a separate heated humidifier.

Applications of HMEs include patients requiring mechanical ventilation via endotracheal or tracheostomy tubes and during anesthesia where ambient gas humidity is low. They are useful when compact circuit components are desired or when active humidification is unavailable or unnecessary. Selection depends on factors such as tidal volume, minute ventilation, and the risk of CO2 retention, aiming to balance adequate humidification with minimal added dead space and resistance.

Limitations and considerations include the potential for increased dead space and airway resistance, mucus plugging or secretion buildup, and reduced effectiveness in cases of airway leaks or very high ventilatory demands. HMEs may be less suitable for patients with thick secretions or high expiratory flows, where a heated humidifier might perform better.

Maintenance involves using disposable HMEs according to manufacturer guidance and institutional protocols, with timely replacement to maintain effectiveness and reduce infection risk.