1. A perfusion trend indicator comprising: an optical sensor that transmits multiple wavelengths of optical radiation into a tissue site, detects the optical radiation after attenuation by pulsatile blood flowing within the tissue site, and generates a sensor signal responsive to the detected optical radiation; a patient monitor that demodulates the sensor signal so as to generate a plurality of plethysmograph channels; a digital signal processor (DSP) within the patient monitor that inputs at least one of the plethysmograph channels and outputs a perfusion parameter accordingly; a perfusion process that executes on the DSP so as to derive a perfusion trend from at least one of the plethysmograph channels, said perfusion trend different than historical values of said perfusion parameter, said perfusion trend responsive to trend values determined during relatively stable portions of said perfusion parameter, said trend values including at least a first baseline value during a first stable portion, a second value during a subsequent second stable portion, and a third value during a subsequent third stable portion, said perfusion trend responsive first to a first smoothed combination of said baseline and second values, and subsequently to a second smoothed combination of said second and third values, said stable portions including at least a plurality of values of said perfusion parameter; and a patient monitor output that is responsive to the perfusion trend.