Automatic Respiratory Gas Monitoring

Abstract

A unique system is described for automatic sequential sampling of airway gases operating on a 24-hour-a-day basis in a 12-bed Shock Trauma Recovery Unit. A series of 50-foot-long sampling lines run from each bed area to a manifold. A small digital calculator each hour automatically places a mass spectrometer in an operative mode, switches a manifold to a calibrating gas, sequentially samples each occupied bed, prints out calculated data, and then reverts to standby status. The analog waveforms from the spectrometer are conditioned for high and low levels corresponding to inspiratory and peak expiratory values of oxygen and peak expiratory carbon dioxide. The waveforms are counted for respiratory rate, and the respiratory quotient is computed. These data are used, in lieu of frequent blood gas determinations, in making estimates of arterial pCO 2 for adjusting respirators and to monitor airway oxygen levels. The system in conjunction with a pneumotachometer is compatible with on-line computer analysis of respiratory gas exchange and mechanics. Using the system, similar data may be obtained off line by collecting mixed expired gases using more conventional techniques and immediate bedside measurement.