A fuzzy system for regulation of the analgesic remifentanil during general anaesthesia

During the last decade, the research group Anaesthesia Control at the University of Rostock (Germany) developed an assistant system to support anaesthetists in the operating theatre. The main objectives during general anaesthesia are appropriate hypnosis, analgesia, relaxation, and stable vital functions. The development of our controllers for hypnosis and relaxation were completed in the last years. The systems were established in the clinical routine in the university hospital. Until now there exists no standard method to measure the state of analgesia or stress response of the patient. In this paper a fuzzy approach is presented to control the application of the analgesic drug remifentanil based on the expert knowledge of anaesthetists. The anaesthetists monitor vital parameters for example arterial blood pressure and heart rate to apply the analgesic drug. Additionally, the heart rate variability was involved as input for the fuzzy analgesia system, which is realized with two controllers, one active at a time. The main controller regulates the continuous rate of remifentanil based on the change in the mean arterial blood pressure, the heart rate and its standard deviation. The second controller calculates a bolus amount of remifentanil based on the absolute values of input parameters, if the heart rate is higher than 90 bpm. Both fuzzy controllers are Mamdani inference systems. The usual time regime for general anaesthesia as well as the minimal and maximal dosage of remifentanil are regarded in the system. The development options of the systems and the first results by controller simulations are discussed.