Adaptation of the quadrupole mass spectrometer to multipatient anaesthesia gas monitoring.

A series of modifications designed to increase the suitability of the quadrupole mass spectrometer for multipatient gas monitoring in the operating suite are presented and evaluated. The adaptations include a pressure-stabilised long capillary inlet system and computer control of the quadrupole filter together with tuning, calibration and subsequent multitheatre analysis and display of clinical information. A pilot study of three months clinical monitoring provided documentation of contributions towards the safety and effectiveness of anaesthesia. These included indication of equipment malfunction, and fluctuations in gas exchange associated with inappropriate ventilation, haemodynamic instability and variations in body temperature. Limited accuracy for carbon dioxide and a low signal-to-noise ratio together with rapid ageing of electron multipliers were identified as problems still only partially solved.