An adaptive controller for the administration of closed-circuit anesthesia during spontaneous and assisted ventilation.

Although reduced waste of expensive anesthetic gases is a strong incentive to use closed-circuit anesthesia, manual methods of performing closed-circuit anesthesia are labor intensive and thus not widely used. Automation of closed-circuit anesthesia delivery may reduce the work. A pressure-based adaptive controller was designed and tested on mongrel dogs to evaluate the feasibility of automating closed-circuit anesthesia using an accessory to an existing clinical anesthesia machine and a gas analyzer. The controller was found stable and responsive with good control of oxygen concentration and acceptable control of halothane end-tidal concentration. The response time for oxygen was 5.23 +/- 1.26 minutes, and that for halothane was 2.67 +/- 1.83 minutes. The average peak overshoot for halothane at the start of the experiment was 26.9%. This pressure controller differs from previously published closed-circuit anesthesia controllers that measure gas volume changes within a mechanical ventilator. A pressure-based controller is easily attached to a standard anesthesia machine and is compatible with modes of ventilation other than controlled mechanical ventilation. The controller used in this study is not designed for clinical use, but was developed to investigate the feasibility of pressure as a basis for gas volume control in closed-circuit anesthesia administration.