Fig. 2. Schematic representation of the application system. Using two xenon-proof tubes (blue ) and xenon-proof sealing devices (green ), xenon or air was delivered into the nasopharyngeal space of the intubated patients at a rate of 1.0 l/h by adjustable peristaltic pumps. A drain tube (ID 1.7 mm) in the mouth of the patient (via a Guedel airway) led to exhaustion. Using endotracheal tubes with inflatable cuffs the tracheobronchial tree was sealed against leakage of respiratory gases or desflurane. In the opposite direction a pulmonary contamination with xenon was avoided.