Automated respiratory gas monitoring of critically injured patients.

Since 1971, we have used a mass spectrometer system for automatic hourly sampling of airway gases on a 24-hour basis in our 12 bed Critical Care Unit. Used in conjunction with arterial and mixed-venous blood samples, the availability of end-tidal O2 and CO2 values allows early identification of increasing AaDO2 and aADCO2 gradients. The ability to monitor end-tidal CO2 allows the monitoring of the adequacy of alveolar ventilation both in patients on and following removal from mechanical ventilation. Continuous information of the end-tidal PCO2 is of particular value in the management of patients with severe head injury.