Abstract: One aspect of the invention provides a patient tissue state monitoring system with a light source; a light detector; a probe adapted to be inserted into a patient to transmit light from the light source to an organ tissue site and to direct light from the organ tissue site to the detector; and a processor programmed to determine tissue state with respect to a tissue site pre-dysoxia point from a fluorescence emission detected by the detector (such as by determining tissue NADH concentration) and to provide an indication of tissue state through an output device (such as by displaying a numerical value corresponding to the fluorescence emission).