In a method and an implantable medical device for assessing a degree of pulmonary edema of a patient, at least two specific body patients of the patent are detected and at least one impedance sensing session is initiated to sense trans-thoracic impedance signals from the patient when the patient is in one of the at least two specific positions. Impedance values are obtained from the impedance signals, and a relation between respective impedance values at the at least two positions is determined. This relation is then used as a metric of pulmonary edema to assess the degree of pulmonary edema, and is provided as an output.