This paper describes PATRICIA, a medical expert system (MES) designed to analyze clinical data, develop adaptive interpretations and elaborate therapeutic guidelines for the management of patients receiving mechanical ventilatory support. PATRICIA is the first application of a new patient-oriented approach that uses two primary modules for representing knowledge. Initially a deterministic module perorms an analysis in which significant demographic and clinical characteristics of each subject are used to speci patient-adapted ranges for clinical variables. Clinical data are then compared to individualized ranges to obtain speciic symbolic information for each patient. The results of the symbolic pre-processing task are then used by the heuristic module to obtain Clinically-adapted conclusions and provide a set of therapeutic options.