A method is described for determining at least one patient-related parameter for monitoring a patient. A general population-related non-linear pressure/CSA relationship of the arterial vascular bed is used and the arterial pressure of the patient is measured to obtain a prediction of the cross sectional area (CSA) of the thoracic part of the aorta. The cross sectional area is measured, wherein at least one parameter of the general population-related non-linear pressure/CSA relationship is corrected by means of the measured cross sectional area to determine a patient-related non- linear pressure/CSA relationship such that the cross sectional area obtained with this patient-related pressure/CSA relationship is equal to the measured cross sectional area.