Heat and Moister Exchangers and the Booster^® System: Technology and Clinical Implications

Abstract

It is well recognized that delivering warm, humidified gas to patients ventilated through an endotracheal or tracheostomy tube is of primarily importance. The upper airway and the normal heat and moisture exchanging process of inspired gases are bypassed during mechanical ventilation with endotracheal intubation or tracheostomy. A continuous loss of moisture and heat occurs and predisposes patients to serious airway damage. In addition, medical gases are dried to avoid condensation damage to valves and regulators in the distribution network. To prevent complications associated with ventilation with cold and dry gases, the addition of exogenous heat and humidity by the use of heated hot water systems (vaporizers or nebulizers) can be considered. Vaporizing humidifiers have some disadvantages: condensation of water that can be a source of infection, malfunctions, high maintenance costs, and increased workload for nursing staff. Heat and moisture exchangers (HMEs) with microbial filtration capacity (HME filters, HMEFs) may be a simple solution to the problems of conditioning respiratory gases and, eventually, of reducing the contamination of the apparatus and subsequent bacterial pneumonia. An important advance in the design of HMEs was made with the introduction of plastic foam impregnated with a hygroscopic substance as the active element. The hygroscopic substance chemically absorbs a portion of the expired water vapor on the humidifier element, which is collected by dry inspiratory gases. Paper-based condensation surfaces have also become available, and their efficiency is reinforced after impregnation with a hygroscopic substance. The HMEs preserve patients’ heat and water, and globally they recover 70% of expired heat and humidity.