Estimating hydration using capillary refill time

A system for determining a capillary refill time in a tissue of a patient, the capillary refill time determined during a capillary refill time period that begins after a period of mechanically-applied blanching pressure on the tissue is released, the system comprising:

• a pressure system providing the mechanically-applied blanching pressure to blanch the tissue to remove a volume of blood in a capillary bed of the tissue;
• a pressure sensor;
• and
• a processor configured to:
• measure the mechanically-applied blanching pressure;
• compare the mechanically-applied blanching pressure to a target pressure;
• control the pressure system to stop increasing the mechanically-applied blanching pressure when the target pressure is achieved;
• receive an optical signal from a light emitter, the optical signal representing light passed through or reflected from the tissue of the patient, the optical signal including signal characteristics indicating a fluctuation in an intensity of the light passed through or reflected from the tissue during the capillary refill time period;
• determine the capillary refill time based on the signal characteristics indicating the fluctuation in the intensity of the light passed through or reflected from the tissue during the capillary refill time period;
• and
• output the capillary refill time.