Abstract
The development of electroencephalographic indices of anaesthetic depth has in turn generated interest in automated anaesthesia delivery systems using these as the input variable. In this paper, one patented closed loop anaesthesia delivery system (CLADS) (502/DEL/2003) is compared to manual control of propofol delivery titrated to the bispectral index (BIS™). Forty ASA I-II patients undergoing elective surgery under general anaesthesia were enrolled in the study. The study participants were randomised using computer generated random numbers to two equal groups. One group received propofol titrated by the CLADS while in the other group (control), anaesthetic delivery was manually titrated to BIS™. Closed loop anaesthetic delivery using our patented system led to lower induction doses of propofol (P<0.05) and less overshoot of the target BIS (P<0.05). The closed loop system maintained BIS to within ±10 of target for a significantly longer time during the maintenance phase of anaesthesia (P <0.01). Smaller amounts of anaesthetic agent were required (P <0.01) and there was faster postoperative recovery (P <0.05). Manual delivery of propofol required the infusion rate to be changed a median of 30 times (IQR 12-45), which required considerable time and attention by the anaesthetist. In conclusion, automated delivery of propofol adjusted to the bispectral index using our CLADS was both effective and efficient as compared to manual control.