Closed loop control of anaesthesia: an assessment of the bispectral index as the target of control

Abstract

SummaryWe 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 closedloop 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.

A randomized controlled trial demonstrates that a novel closed-loop propofol system performs better hypnosis control than manual administration

“…7 Previous studies have shown that the BIS is well suited as a control variable for closed-loop systems. 1,2,[8][9][10][11] Also, studies have shown that closed-loop systems using the BIS outperform manual control. 3,5,6 Relying on a single input signal, the controller can be misled by artefacts that can occur on the EEG signals, and this poses an inherent safety risk to the patient.…”

Feasibility of Closed-loop Titration of Propofol and Remifentanil Guided by the Spectral M-Entropy Monitor

“…A closed-loop controller was described with the BIS Monitor and a fixed mixture of propofol and alfentanil. 7 Use of an isoboller controller has also been de- Data are presented as median ͓interquartile range͔ or number (%) of total patients of each group. Time to tracheal extubation was defined as the time from discontinuation of propofol and remifentanil infusion until tracheal extubation.…”

Towards a Multivariable Model for Controlling the Depth of Anaesthesia using Propofol and Remifentanil

“…The Bispectral index (BIS) is a single composite measure derived from the spontaneous EEG and has been proven to have a high sensitivity and specificity to measure anaesthetic drug effect (Morley et al, 2000;Struys et al, 2003). BIS is now recognized as one of the reference measures of DOA for closed loop control purposes (Ionescu et al, 2008;Absalom et al 2011;Liu et al, 2011).…”

“…Analgesics block the sensation of pain; the hypnotics produce unconsciousness, while the muscle relaxants prevent unwanted movement of muscle tone. The relationship between the hypnotic drug, Propofol, administered during general anaesthesia, and BIS (a signal derived from the electroencephalogram used to assess the level of consciousness during anaesthesia) is widely documented and several studies regarding the interaction model of Propofol and Remifentanil can be found in the literature (Morley et al, 2000;Struys et al, 2003;Absalom et al, 2011). When inducing and maintaining anaesthesia, anaesthesiologists select initial doses based on a variety of considerations, they observe the results, and then make adjustments based on several factors, at irregularly varying intervals.…”