Optimum humidification of air administered to a tracheostomy in dogs. Scanning electron microscopy and surfactant studies.

The effect of the inhalation of dried (less than 40% water-saturation) or humidified air (100% water-saturation at 25, 30, 35 and 40 degrees C) was studied in dogs in which a tracheostomy had been performed to determine the optimal humidity. After inhalation for various periods, the dogs were killed and pieces of lung tissue were excised for analysis of surfactant. Sections of the trachea and the primary to tertiary bronchi were taken for scanning electron microscopic examination. Structural changes were observed in the trachea of dogs inhaling dried at and in the tertiary bronchi of dogs inhaling 100% water-saturated air at 35 degrees C. No changes was observed after 24 h in dogs which had inhaled 100% water-saturated air at 25 degrees C under anaesthesia or at 30 degrees C without anaesthesia. Consequently, the optimal range of humidity was determined to be 100% water-saturation between 25 and 30 degrees C.