Ventilator alarm nonfunction associated with a scavenging system for waste gases.

A 73-year-old man underwent a bitemporal scalp flap and advancement for squamous cell carcinoma of the scalp. After induction of anesthesia and tracheal intubation, ventilation was controlled with a Ventimeter Ventilator (#20-000-70, Narco Scientific, Air Shields Division, Hatboro, PA). Exhaust from the ventilator was collected by a Scavenging Waste Gas Interface Valve (#216-6739-671, Ohio Medical Products, Division of Airco, Madison, WI) connected to wall suction. Anesthesia was maintained with N20-02 (3:2 Limin) and fentanyl. Muscle relaxation was provided by pancuronium. One hour later, breath sounds heard through the esophageal stethoscope suddenly ceased. The ventilator bellows continued to function normally and the audio disconnect alarm was not activated. Airway pressure within the circle absorber was zero and a quick examination of the breathing hoses under the surgical drapes revealed disconnection from the endotracheal tube. The circuit was reconnected, ven-