The invention refers to a method of determining an indicator that is representative for a patients volume responsiveness, comprising the following steps: (i) measuring a sequence of pulse signals of a patient (ii) determining an envelope(signal)-curve based on the sequence of measured pulse signals (iii) determining a fit(envelope(signal))-function based on the previously determined envelope(signal)-curve, the fit(envelope(signal))-function representing an idealised curve progression of the envelope(signal)-curve without comprising pulse variations caused by ventilation or respiration induced heart-lung interaction (iv) determining respiratory pulse variation signals corresponding to the pulse variations caused by ventilation or respiration induced heart-lung interaction (v) determining an envelope(respiration)-curve based on the previously determined respiratory pulse variation signals (vi) determining a fit(envelope(respiration))-function based on the previously determined envelope(respiration)-curve, the fit(envelope(respiration))-function representing an idealised curve progression of the envelope(respiration)-curve (vii) determining the indicator that is representative for the patients volume responsiveness based on the fit(envelope(signal))-function and the fit(envelope(respiration))-function. The invention also relates to a logic unit and a system, both for determining an indicator representative for the patients volume responsiveness.
