Guided closed loop control of analgesia: Are we there yet?

This paper presents the latest state of art and developments in the quest for completing the challenging control of anesthesia, i.e the missing part of regulating analgesia. Drug rate to effect modelling and closed loop control of hypnosis and neuromuscular blockade seem to have been well characterized and successful in clinical practice. By contrast, analgesia remains an intricate process with multiple physiological stages at multiple scales in time and in body loci. Latest developments with fractional order kinetics and fractional order impedance models rise hope to the horizons yet to come. A perspective forms on the next steps to be tackled to achieve the complete guided control paradigm.