During most surgical procedures the patient is paralyzed and must depend completely on the anesthesiologist to maintain such vital physiologic functions as breathing and heart rate. It is therefore not surprising that with relatively few effective physiological monitors available to the anesthesiologist, the frequency of mishaps is high. Of the approximately 20 million surgical procedures preformed annually in this country, it is estimated that about 6,000 people die or become seriously disabled as a result of the anesthetic procedure. Anesthesia monitoring can be divided into 1) monitors which primarily check the performance of the anesthesia delivery system and 2) monitors which are aimed at measuring the physiological effects of anesthetic the precedure on the patient. The goal of this proposed work is to extend the capabilities of a monitoring system (presently designed for performance checking) for monitoring of physiological variables. The proposed system will be capable of continuously monitoring circulation, ventilation, and gas exchange variables. Anesthetic gas uptake and tissue concentration are by-product measurements of the method. The key to economical and high quality measurements of these cardiopulmonary parameters is the development of a miniaturized, high quality mass spectrometer, already competitively priced for service as just an anesthetic gas monitor. However, since this analyzer represents the major cost of a total anesthesia/physiologic monitoring system, the physiological monitoring addition represents a very substantial monitoring benefit at a disproportionately modest cost.