Two-degree-of-freedom control scheme for depth of hypnosis in anesthesia ⁎ ⁎This work has been partially funded by the following projects: DPI2014-55932-C2-1-R, DPI2014-55932-C2-2-R, DPI2014-56364-C2-1-R and DPI2012-31303 financed by the Spanish Ministry of Economy and Competitiveness and EU-ERDF funds); and the UNED through a postdoctoral scholarship.