Effect of a heat and moisture exchanger on temperature and humidity of inhaled gas in isoflurane-anesthetized dogs

OBJECTIVE:To investigate the effects of a heat and moisture exchanger (HME) on the temperature and humidity of inhaled gas in isoflurane-anesthetized dogs. STUDY DESIGN:Prospective, interventional study. ANIMALS:A total of four experimental dogs and four client-owned dogs weighing 13.9 ± 7.4 kg (mean ± standard deviation). METHODS:The four experimental dogs were anesthetized on two occasions with and without an intact HME at least 1 week apart. The four client-owned dogs were anesthetized once only for a surgical procedure and assigned to the HME group or no-HME group in alternate order, resulting in six dogs for each group. All dogs were premedicated, anesthetized with propofol and intubated. The HME was connected to the endotracheal tube. Anesthesia was maintained with isoflurane. A digital thermo-hygrometer was placed between the endotracheal tube and HME. The temperature and relative humidity of the inhaled gas were measured every 5 minutes for 60 minutes and the absolute humidity was calculated at each time point. RESULTS:The temperature and absolute humidity of the inhaled gas was significantly higher at 5-60 minutes after intubation in the HME group than in the no-HME group. Absolute humidity was maintained above 29 mg H2O L-1 in the HME group. No significant time-dependent effects on temperature, relative humidity or absolute humidity of the inhaled gas were observed. CONCLUSIONS AND CLINICAL RELEVANCE:The temperature and absolute humidity of the inhaled gas were higher when an HME was used during isoflurane anesthesia in dogs. The use of an HME may reduce the risk of dehydration and dysfunction of the airway mucosal epithelium.