A monitoring device (29) is included in a medical system to implement a method for prediction of a rapid symptomatic drop in a subjects blood pressure, e.g. during a medical treatment such as dialysis. To this aim, a pulse shape parameter (p ) with respect to a pulse generator of the subject is registered by means of a pressure sensor (4a, 4b, 4c) arranged in an extracorporeal blood flow circuit coupled to a cardiovascular system of the subject (P). The pressure sensor (4a, 4b, 4c) is adapted to detect pressure variations in blood vessels of the subject (P). It is investigated, during measurement period, whether or not one or more of the pulse shape parameters fulfil a decision criterion. An output signal (α) is generated if the decision criterion is found to be fulfilled, to indicate a predicted rapid symptomatic blood pressure decrease in the subject (P). The decision criterion may operate on pulse magnitude measures calculated for the received pulse shape parameters (p), or statistical dispersion measures calculated based on the thus-calculated pulse magnitude measures.
