1. A physiologic parameter monitor, comprising: a processor that determines a parameter value indicative of a response of a human or animal subject to fluid intake during fluid therapy based on an impedance cardiographic (ICG) output signal, wherein the processor is configured to: determine a stroke volume value, for a plurality of heartbeats, based on an area under respective ICG output signal waveforms from when the aortic valve opens to when the aortic valve closes; determine a respiratory rate value, for the plurality of heartbeats, based on peaks of the respective ICG output signal waveforms over a predetermined time period; and determine the parameter value based at least on the determined stroke volume value and the determined respiratory rate value as a change in the determined stroke volume divided by the determined respiratory rate; and a display that displays the parameter value in a human readable format.