Noninvasive methods and apparatus for detecting blood volume imbalances in a mammalian subject are disclosed. The method includes obtaining baseline measurements of at least three physiological parameters from a subject wherein the parameters are selected from the group consisting of heart rate, electrical body impedance, skin temperature, perfusion index, peripheral blood flow and skin humidity. Measurements of electrical body impedance, skin temperature, perfusion index, peripheral blood flow and skin humidity are taken at one or more extremities of the subject such as the calf, ankle, forearm, thigh, fingers and toes. The physiological parameters for which baseline measurements were obtained are then monitored to detect changes from the baseline measurements that indicate blood volume imbalances. A preferred embodiment comprises computing a baseline blood volume index from the baseline value measurements of each parameter to be monitored and then carrying out the step of monitoring by obtaining real time (current) value measurements of these parameters which are inputted into an algorithm which computes a real time (current) blood volume index based upon the differences between the baseline and real time (current) value measurements.
