The effect of a heat and moisture exchanger (HME) on bronchial mucus transport in a closed inhalation anesthesia system

Abstract

The administration of dry anaesthetic gases for ventilation leads to morphological changes of the tracheobronchial epithelium that may cause postoperative pulmonary complications. Therefore, additional humidification with a heat and moisture exchanger (HME) is suggested for ventilation during anaesthesia, particularly when using semi-open breathing systems. Recommendations concerning the use of a HME in the semi-closed system are controversial. There are no data in the literature as to whether a HME improves mucociliary transport under these conditions. We therefore studied bronchial mucus transport velocity (BTV) with and without the use of a HME in the semi-closed circle system in humans. The study was approved by the ethics committee of our hospital. In a prospective, randomised trial a total of 22 patients undergoing major abdominal surgery were investigated. In all patients anaesthesia was induced and maintained with midazolam, fentanyl, and vecuronium. After intubation, a HME (BACT/VIRAL HME, Pharma Systems AB, Sweden) was inserted between the endotracheal tube and ventilation tubing in 11 patients; the other 11 were ventilated without a HME and served as controls. Ventilation was assisted with a fresh flow of 3 in a semi-closed system (Dräger Sulla 808 V with an 8 ISO circle system and Ventilog 2 ventilator, Drägerwek AG, Germany) and a 2:1 mixture of nitrous oxide and oxygen. The fresh gas passed through the soda lime canister. At the end of the operation BTV was measured with a small volume of albumin microspheres labeled with technetium Tc99m, which was deposited on the dorsal surface at the lower ends of the right and left main bronchi via a catheter placed in the inner channel of a fibre-optic bronchoscope. The two groups were comparable with regard to age, sex, preoperative lung function, duration of mechanical ventilation, and dose of anaesthetics. There were no statistically significant differences in the BTVs. BTV does not improve with the use of a HME in the semi-closed circle system with a fresh gas flow of 31. With modern anaesthesia machines lower fresh gas flows should be administered, whereby the humidity and temperature of the inspired gases are further increased.