Quantitative Anaesthesia with the Help of Closed-Loop Control
Closed-loop control systems have been used since the time of the Babylonians, when irrigation systems were opened and closed in closed-loop control mode . Closed-loop control in anaesthesia began in 1950 when Bickford used the EEG signal to control the infusion of thiopental . A syringe with thiopental was attached to a stepper motor. Each time the EEG crossed zero, a bolus of thiopental was given. As the patient became anaesthesized the infusion rate slowed because the frequency of the EEG decreased. Closed-loop control has adjusted ventilation during anaesthesia by comparing the difference between the desired and a measured end-tidal carbon dioxide concentration . If the CO2 was high, the inspiratory airway pressure was incremented in 0.1-mm steps. When the end-tidal reached the desired level, the airway pressure was held constant. The most common application of closed-loop control is the maintenance of arterial blood pressure by the infusion of sodium nitroprusside . Experience has shown that a desired end-tidal anaesthetic orblood pressure is maintained more consistently andmore accurately under closed-loop control than is done manually . Closed-loop control can perform some very usedful and helpful tasks when it is made available in the anaesthesia machine design.
KeywordsDioxide Dopamine Respiration Syringe Hull
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