1. Blitt CD (1990) A philosophy of monitoring. In: Blitt CD (ed) Monitoring in anesthesia and critical care medicine, 2nd edn. Churchill Livingstone, New York Edinburgh London, pp 3–8
2. Braun U, Hempel V (1992) Überwachung während der Anästhesie. In: Doenicke A, Kettler D, List WF, Tarnow J, Thomson D (Hrsg) Anästhesiologie, Lehrbuch der Anästhesiologie und Intensivmedzin 1, 6. Aufl. Springer, Berlin Heidelberg New York Tokyo, S 289–319
3. Dornette WHL (1973) The stethoscope–the anesthesiologist’s best friend. In: Dornette WHL (ed) Monitoring in anesthesia. Davis, Philadelphia, pp 75–84
4. Ehrenwerth J (1993) Reaching the limits of technology? ASA Newsletter 57 (8): 8–9
5. Guedel AE (1920) Third stage ether anesthesia: A subclassification regarding the significance of the position and movement of the eyeball. Am J Surg 34: 53