Anesthesia machine having proportion limiting control system

TL;DR: In this article, a system for providing an interconnection between two needle valves such that movement of either needle valve, in opening or closing thereof, is affected or limited by movement of the other valve is described.

Abstract: A system is disclosed for providing an interconnection between two needle valves such that movement of either needle valve, in opening or closing thereof, is affected or limited by movement of the other valve. The invention is particularly suited to an anesthesia machine wherein separate supplies of oxygen (O 2 ) and nitrous oxide (N 2 O) are fed to individual needle valves which are then individually adjusted to provide a desired mixture of N 2 O and O 2 for administration to a patient to anesthetize the same. The system herein disclosed interconnects the individual needle valves such that the O 2 needle valve may be opened fully without restriction, however, when the N 2 O valve is open, the interconnection provides that closing of the O 2 valve will, at a predetermined point, also correspondingly close the N 2 O valve, thus preventing the percentage of N 2 O in the mixed gas from raising above a set value, i.e. one at which sufficient oxygen for a respirable mixture is assured. Similarly, the N 2 O valve is prevented, through the same interlock system, from being opened beyond a point where the N 2 O percentage could exceed such limit. Again, when the N 2 O valve reaches the predetermined point, further opening of the N 2 O valve also opens the O 2 valve such that the flow can be increased by further opening of the N 2 O valve but the percentage of N 2 O and O 2 will thereafter remain constant. In addition, the overall system has a further preventative feature where the flow of oxygen cannot be set below a predetermined value so that sufficient oxygen flow to the patient is assured.