A system extrapolates and interpolates patient fluid intake or output parameter values and associated cumulative values over variable time intervals from a reduced set of stored fluid parameter values affecting fluid cumulative volume computation or rate of fluid intake or output computation. The extrapolation and interpolation function accomodates drip (continuing) fluid volumes as well as supplemental (non-continuing e.g., bolus) fluid volumes. A patient medical parameter data processing system provides patient medical parameter data for trend indicative display covering a time period comprising user selectable patient parameter acquisition time intervals. The system includes an acquisition processor for receiving data identifying, for a continuing infusion, rate of volume of fluid infusion into a patient, a fluid type identifier and a start time and start date of said continuing infusion. The received data also identifies for a non-continuing infusion, a total volume of fluid infusion, a fluid type identifier and a time and date of the non-continuing infusion. A data processor determines, from the received data, a cumulative total volume infusion of a particular fluid into a particular patient for a particular user selectable patient parameter acquisition time interval.