title: Closed loop control of anaesthesia: an assessment of the bispectral index as the target of control.
abstract: We investigated the performance of a closed-loop system for administration of general anaesthesia, using the bispectral index as a target for control. One hundred patients undergoing gynaecological or general surgery were studied. In 60 patients, anaesthesia was maintained by intravenous infusion of a propofol/alfentanil mixture. In 40, an isoflurane/nitrous oxide based technique was used. For each technique, patients were randomly allocated to receive either closed-loop or manually controlled administration of the relevant agents (propofol/alfentanil or isoflurane), with an intra-operative target bispectral index of 50 in all cases. Closed-loop and manually controlled administration of anaesthesia resulted in similar intra-operative conditions and initial recovery characteristics. During maintenance of anaesthesia, cardiovascular and electro-encephalographic variables did not differ between closed-loop and manual control groups and deviation of bispectral index from the target value was similar. Intra-operative concentrations of propofol, alfentanil and isoflurane were within normal clinical ranges. Episodes of light anaesthesia were more common in the closed-loop group for patients receiving propofol/alfentanil anaesthesia and in the manual group for patients receiving isoflurane/nitrous oxide anaesthesia. Convenience aside, the closed-loop system showed no clinical advantage over conventional, manually adjusted techniques of anaesthetic administration.
authors.affiliation: Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: A
authors.initials: A
authors.lastname: Morley
authors.forename: J
authors.initials: J
authors.lastname: Derrick
authors.forename: P
authors.initials: P
authors.lastname: Mainland
authors.forename: B B
authors.initials: BB
authors.lastname: Lee
authors.forename: T G
authors.initials: TG
authors.lastname: Short
mesh_terms: D000328:Adult; D015760:Alfentanil / Q000008:administration & dosage; D000764:Anesthesia, Closed-Circuit / Q000379:methods*; D000771:Anesthesia, Intravenous / Q000379:methods*; D019162:Anesthetics, Combined / Q000008:administration & dosage; D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D004334:Drug Administration Schedule; D016503:Drug Delivery Systems; D004569:Electroencephalography / Q000187:drug effects*; D005246:Feedback; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009609:Nitrous Oxide / Q000008:administration & dosage; D015742:Propofol / Q000008:administration & dosage
chemical_list: D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D015760:Alfentanil; D007530:Isoflurane; D009609:Nitrous Oxide; D015742:Propofol