Feedback control is engineering, let's treat it as such.

Ngai Liu, Thierry Chazot, Antoine Genty, Alain Landais, Aymeric Restoux, Kathleen McGee, Pierre-Antoine Laloë, Bernard Trillat, Luc Barvais, Marc Fischler, Titration of propofol for anesthetic induction and maintenance guided by the bispectral index: closed-loop versus manual control: a prospective, randomized, multicenter study. Anesthesiology. ,vol. 104, pp. 686- 695 ,(2006) , 10.1097/00000542-200604000-00012

Tom De Smet, Michel M. R. F. Struys, Scott Greenwald, Eric P. Mortier, Steven L. Shafer, Estimation of optimal modeling weights for a Bayesian-based closed-loop system for propofol administration using the bispectral index as a controlled variable: a simulation study Anesthesia & Analgesia. ,vol. 105, pp. 1629- 1638 ,(2007) , 10.1213/01.ANE.0000287269.06170.0F

Ngai Liu, Morgan Le Guen, Fatima Benabbes-Lambert, Thierry Chazot, Bernard Trillat, Daniel I. Sessler, Marc Fischler, Feasibility of closed-loop titration of propofol and remifentanil guided by the spectral M-Entropy monitor. Anesthesiology. ,vol. 116, pp. 286- 295 ,(2012) , 10.1097/ALN.0B013E318242AD4F

Ngai Liu, Thierry Chazot, Sophie Hamada, Alain Landais, Nathalie Boichut, Corinne Dussaussoy, Bernard Trillat, Laurent Beydon, Emmanuel Samain, Daniel I. Sessler, Marc Fischler, Closed-loop coadministration of propofol and remifentanil guided by bispectral index: a randomized multicenter study. Anesthesia & Analgesia. ,vol. 112, pp. 546- 557 ,(2011) , 10.1213/ANE.0B013E318205680B

Gregory Crosby, Deborah J. Culley, Processed Electroencephalogram and Depth of AnesthesiaWindow to Nowhere or into the Brain Anesthesiology. ,vol. 116, pp. 235- 237 ,(2012) , 10.1097/ALN.0B013E318242B2FF

Tom De Smet, Michel M. R. F. Struys, Martine M. Neckebroek, Kristof Van den Hauwe, Sjoert Bonte, Eric P. Mortier, The accuracy and clinical feasibility of a new Bayesian-based closed-loop control system for propofol administration using the bispectral index as a controlled variable Anesthesia & Analgesia. ,vol. 107, pp. 1200- 1210 ,(2008) , 10.1213/ANE.0B013E31817BD1A6