Abstract: A system for assessing organ function has a plurality of light emitters of distinct spectral characteristics are coupled into a percutaneous fiber delivery assembly with a tip extending to or into an internal organ to illuminate organ tissue. The assembly includes a delivery optical fiber, and a collection fiber that collects and returns light scattered, reflected or emitted by the surrounding tissue to a detector at the proximal end. The device also senses temperature at the tip. Control and processing modules drive the laser diodes and process the return signals. The instrument may assess general metabolic activity by detecting light absorption of a linked substance, for example at a peak attributed to deoxygenated hemoglobin and/or at one or more peaks attributed to oxygenated hemoglobin. Preferably, change of a parameter such as pulse oxygen saturation together with one or more other parameters such as temperature are detected to provide an indication of organ function, e.g., the onset of shock.