Humidification of the airways. Adequate for function and integrity?

gastrointestinal hemorrhage by irradiation with a power neo-dymium-YAG laser. 8 Cortese DA, Kensey JH. Endoscopic management of lung cancer with hematoporphyrin derivative phototherapy. Photoradiation therapy in the treatment of advanced cancer of the trachea and bronchus. Chest (in press) 11 Dougherty TJ. Photoradiation therapy (PRT) of malignant tumors. In: Critical review in oncology-hematology. he upper respiratory tract serves as an air condi-T t i o n i n g system; particulate matter is entrapped while inspired air is warmed and humidified prior to entry into the major airways. Turbulent flow through the nose and pharynx propels solid particles towards the surface, enhances convective transfer of heat from the mucosa, and increases the apparent surface area of exposure for evaporation of water vapor into the air stream. Because the nasal mucosa becomes cooled in the process, exhaled gas, which is fully humidified at body temperature, gives up water vapor to the cooler surface and the effluent gas temperature is reduced to 32-34°C.' Fully saturated air at this temperature contains 10.2 mg/L less water vapor than alveolar gas. Water and heat recapture by this mechanism conserves 20-25 percent of insensible losses during normal breathing in temperate atmospheric conditions.' The administration of relatively dry anesthetic gases and oxygen-enriched mixtures via an endotracheal tube obliges the lower respiratory tract to perform these functions. The potential hazard of greater heat and water losses, as well as structural damage was appreciated early in tracheotomized patients, and external application of humidity was demonstrated to alleviate excess mucus production and encrustation of secretions. Much subsequent study has revealed the sensitivity of the tracheobronchial tree to incompletely humidified gas. Cessation of ciliary beating occurs within ten minutes of exposure of the trachea to 50 percent relative humidity.' Tracheal mucus velocity, studied in intact dogs,5 was reduced by half after one hour of breathing dessicated room air and completely ceased after three hours. Subsequent rehumidification of the airway rapidly restored tracheal mucus velocity, but histologic evidence demonstrated that extensive inflammation and sloughing of ciliated epithelium in the trachea and bronchi were present despite the functional restoration observed. Cytologic studies in anesthetized human subjects confirmed that damage to the tracheal epithelium occurs within two hours of administration of dry gases through an endotracheal tube, whereas gases at 60 percent relative humidity produce no damageas However , air at 60 percent relative humidity delivered through an endotracheal tube reaches only 83 percent …