Heat and Moisture Exchangers (HMEs)
A heat and moisture exchanger (HME), also very appropriately called an "artificial nose" or "mist collar", is used for this purpose. An HME retains part of the moisture and heat that is contained in the air exhaled through the HME and releases it back into the respiratory tract during inhalation. Moreover, an HME reinstates the expiratory resistance that is lost and that normally keeps the pulmonary alveoli open to improve the oxygen supply to the blood. In this way, similar pressure conditions in the lung are maintained as those that prevailed prior to the surgical intervention. Without an HME, the respirated air would be too cold and too dry and there would be no respiratory resistance either.
Additionally, the early use of an HME (immediately after surgery) helps prevent the formation of mucous plugs. Without an artificial nose, the tracheal mucosa will dry out within just a few minutes, which can lead to the formation of mucous plugs and significantly increase the risk of infection. An HME can moreover act as an effective filter for foreign bodies (for example, by retaining dirt and dust particles and even insects). Hence, the use of an HME is highly recommended.