An automated mechanism for protection of mass spectrometry sampling tubing

The usefulness of medical mass spectrometers in intensive care units can be limited by too frequent obstruction of the tubing that transports gases from the patients to the analyzing unit. To overcome this problem, we developed an automated system consisting of an infrared light sensor and a three-way valve. One port of the three-way valve connects to 2.4-m disposable tubing that collects gases from the patient's airway. The second port is connected to a mass spectrometer analyzing unit through 30-m permanently installed tubing. The third port is connected to a pressurized oxygen source. An infrared light sensor is placed on the shorter tubing, between the patient and the three-way valve. When increased optical density is detected, due to entrainment of respiratory secretions, the three-way valve is activated. Gas flow is closed between the patient and the mass spectrometer and opened between the pressurized oxygen source and patient tubing to flush its contents. During the six years that the protection system has been in use, the frequency with which the disposable gas collection tubing is changed has been halved. Furthermore, periodic tests of delay and response times, performed at each bedside station, indicate that permanent connection tubing only needed cleaning at 2- to 3-year intervals. The system has decreased the cost of operating our mass spectrometers while also reducing periods of unavailability due to equipment failure.