Innovative System Regulates Anesthesia via Computer

A novel system detects the hypnotic state of the sedated patient at all times and automatically controls anesthesia during surgical operations.

The new system developed by researchers at the at the University of La Laguna (ULL; San Cristobal De La Laguna Spain) and the University Hospital of the Canary Islands (HUC; San Cristobal De La Laguna, Spain), uses sensors and a monitor to record the patient's electroencephalogram (EEG) and bispectral index (BIS), a parameter that measures hypnotic state and relates this to the patient's level of consciousness. The BIS value fluctuates between 100 (the maximum possible state of alertness) and 0 (lack of cortical electrical activity, the state of deepest unconsciousness). The researchers focused on the BIS region involved in general anesthesia, between 40 and 60.

The data are processed by a computer with a specific control software application that is based on adaptive proportional integral derivative (PID) algorithms with dead-time compensation, a control-loop feedback mechanism that automatically regulates the right dose according to the measured and desired values by controlling the pump that injects the anesthetic. The control methods are based in the use of PID controllers using the Smith predictor to avoid undesirable oscillations in the BIS signal during the process. To validate the technique, the researchers carried out simulations using various models, and tested it on 15 volunteer patients (aged between 30 and 60) at the HUC. The study describing the new system and the validation process was published in the December 2009 issue of Computer Methods in Biomechanics and Biomedical Engineering.

"This is an efficient control technique which regulates anesthesia in operating theatres by computer, with the aim of adapting the dose of the drug administered according to the individual characteristics of each patient,” said lead author Juan Albino Méndez, a researcher in the anesthesia control group at ULL. "The first results obtained both in surgery and in the simulations show that the system operates very satisfactorily, and has surgical applications with well-founded expectations of success.”

The BIS is an EEG-derived multivariate scale that correlates with the metabolic ratio of glucose; from this metabolic activity the brain obtains the ability to capture information from both outside and inside the body and integrate that information into conscious perception, with the ability to remember it later. Both loss of consciousness and awakening from anesthesia are correlated with this scale.

Related Links:
University of La Laguna
University Hospital of the Canary Islands