Expired gas monitoring by mass spectrometry in a respiratory intensive care unit.

The application of a medical mass spectrometer for the monitoring of respired gases in the respiratory intensive care unit of a community hospital is reviewed. This monitoring system is routinely used with intubated patients for periodic monitoring of end-tidal CO2 tensions (PETCO2), FIO2, and PETO2 dead space to tidal volume ratios, and the determination of AaDO2; the value of these measurements is discussed. It is especially useful for continuous monitoring at critical points in the patient's course such as weaning from the ventilator, determining optimal ventilator settings, monitoring, unstable nonintubated patients, and in better defining the pathophysiological disturbances impeding patient progress, examples of which are presented. Preliminary observations suggest it may also provide a simple technique for determining optimal expiratory retard settings. The initial cost of such a system is justified by the benefit to the patient, i.e., reduction in the frequency of nonessential arterial blood gas determinations, shortened weaning period, and early detection of potentially dangerous trends. Technical problems encountered with this system and potential future uses are also discussed.