A Heat and Moisture Exchanger (HME) is a passive medical device that serves as an artificial nose for individuals whose upper airway function has been compromised. This small, disposable unit conditions the air entering the lungs, taking over the functions of warming, humidifying, and filtering that the nose and throat naturally perform. The device is placed over the opening in the neck, known as a stoma, through which a person breathes. Its primary function is to retain heat and moisture from exhaled air and transfer it back into the inhaled air, ensuring the lungs receive air at a more appropriate temperature and humidity level.
The Essential Role of Heat and Moisture Exchange
The human upper airway is responsible for conditioning inhaled air before it reaches the delicate tissues of the lungs. Without this conditioning, the lungs are exposed to cold, dry air, which can cause irritation and damage to the airway lining. The HME is designed to mimic this process, which is why it is often referred to as an artificial nose.
The device contains a material, such as treated foam or corrugated paper, often impregnated with hygroscopic salts like calcium chloride, which helps to retain water. As a person exhales, warm, moisture-rich air passes through this material, depositing heat and condensing water vapor onto the surface. During the subsequent inhalation, the cooler, drier ambient air moves through the HME, picking up the stored heat and moisture before continuing into the lungs.
This continuous exchange mechanism ensures the air entering the trachea is significantly warmer and more humid than unconditioned air. The physiological benefit is a reduction in the body’s need to produce excessive, thick mucus, a common reaction to dry air irritation. Consistent HME use helps to maintain the health of the airway lining, leading to a reduction in coughing and the overall risk of respiratory complications.
Patient Populations Who Rely on HMEs
The primary patient groups who rely on HMEs are individuals who have undergone specific surgical procedures that alter their breathing pathway, most commonly a total laryngectomy or a tracheostomy. A total laryngectomy involves the removal of the larynx, or voice box, permanently separating the upper and lower airways. Breathing is then done exclusively through a surgically created opening in the neck called a stoma.
Because the air now bypasses the nose and mouth entirely, the natural functions of filtering, warming, and humidifying are lost. The HME is placed directly over this stoma to restore these functions, which is considered the standard of care following a laryngectomy. The device also helps protect the lungs from airborne particles and dust.
A tracheostomy involves creating a stoma in the neck and inserting a tube into the trachea to facilitate breathing. The HME is commonly used for spontaneously breathing patients to provide portable and convenient humidification. Long-term HME use in both populations results in a significant decrease in respiratory symptoms, such as the frequency of coughing and excess mucus production. Certain HME models can also incorporate a speaking valve, enabling hands-free speech by diverting air through the prosthesis.
Daily Care and Replacement of the Device
HMEs are designed as single-use disposable cassettes that require regular replacement to maintain their effectiveness and hygiene. The typical maximum lifespan for a cassette is 24 hours, and it should be discarded immediately if it becomes visibly soiled or clogged with mucus. A clogged HME increases the resistance to airflow, making it harder to breathe, which signals the need for changing.
The cassette must be securely attached to the stoma, either by connecting to a tracheostomy tube or by fitting into an adhesive baseplate applied to the skin around the stoma. Users must not attempt to wash or rinse the HME to clean it. Doing so removes the hygroscopic salts and renders the device completely ineffective at retaining moisture, potentially increasing the risk of infection.
Consistent use, ideally 24 hours a day, is necessary to achieve the full pulmonary health benefits. Different types of HMEs are available to suit various activities and environments, balancing filtration, humidification, and breathing resistance:
- A model with higher filtering capacity may be recommended for dusty environments or during flu season.
- A “HighFlow” version might be better suited for physical exertion.
- Some HMEs feature an integrated speaking valve, allowing the user to speak without manually covering the device.