Heat and moisture exchanger

Heat and Moisture Exchangers (HME) are devices used in mechanically ventilated patients intended to help prevent complications due to 'drying of the respiratory mucosa, such as mucus plugging and endotracheal tube (ETT) occlusion.' HMEs are one type of commercial humidification system, which also include non-heated-wire humidifiers and heated-wire humidifiers. Heat and Moisture Exchangers (HME) are devices used in mechanically ventilated patients intended to help prevent complications due to 'drying of the respiratory mucosa, such as mucus plugging and endotracheal tube (ETT) occlusion.' HMEs are one type of commercial humidification system, which also include non-heated-wire humidifiers and heated-wire humidifiers. HMEs have been in clinical use for over 30 years. An HME cassette plays a central part of lung rehabilitation after a total laryngectomy. Humidification and suctioning are necessary to manage secretions in patients on mechanical ventilation. According to Branson (2007), the optimal humidification level 'has been not well defined, but it is clear that in a patient with thick and copious secretions a heated humidifier is preferred to an HME'. In patients with acute lung injury and acute respiratory distress syndrome conventional humidifiers are preferred to HMEs for improved elimination of carbon dioxide. An HME has three purposes in laryngectomy: In the lungs a temperature of 37 °C and 100% relative humidity (RH) is the ideal condition for the ciliary activity. If the conditions are too warm or cold, the cilia beat slower and at some point not at all. During normal nasal inspiration, air of 22 °C and 40% RH is conditioned into air of 32 °C and 99% RH at the level of the trachea. The effect of the increased resistance (compared to stoma breathing without HME) in laryngectomy patients is poorly understood, but HMEs add a variable resistance to the airflow resistance, depending on the flow rate, though the outcomes of studies are not consistent. HME cassettes with an electrostatic filter are designed to enhance the protection against airborne microbes to help to reduce the transfer of viruses and bacteria. Wearing an HME cassette does not compensate for the loss of upper airway filtration of smaller particles such as bacteria and viruses; the pores of the HME filter are larger than the diameter of the infectious particles. Only larger particles are filtered by the HME.