A system for monitoring the transcutaneously measured partial pressure of oxygen at a measuring site of a patient, comprising: a sensor for transcutaneously measuring the partial pressure of oxygen at the measuring site, the sensor comprising: - a heating element, for heating a skin of the patient at the measuring site, - a control unit for controlling the temperature of the heating element, processing of the sensor signals, and controlling communication between the sensor and a monitor of the system for displaying the measured partial pressure of oxygen, the control unit further being adapted to control the heating element to cycle the temperature of the skin at the measuring site between a lower and a higher temperature by: - adjusting and maintaining, by the controller and the heating element, the measuring site at a temperature close to body core temperature in a first time interval so that the skin temperature at the measuring site is maintained at the lower temperature, and - increasing and maintaining, by the controller and the heating element, the temperature at the measuring site in a second time interval so that the skin temperature at the measuring site is maintained at the higher temperature, which is at least 41 0 C, wherein the controller is configured so that the first time interval is longer than the second time interval; wherein the controller and the heating element are configured so that the sequence of first and second time intervals is repeated for performing the cycling of the temperature of the skin at the measuring site; wherein the system further comprises means for communicating between the sensor and the monitor; and wherein the system is further configured to: show measured levels at the monitor for points in time when the skin temperature is sufficient for reliable meausures; and show, at the monitor, extrapolated levels which are extrapolated from one or more of the measured levels for points in time when the skin temperature is such that the measures cannot be relied upon directly. a sensor for transcutaneously measuring the partial pressure of oxygen at the measuring site, the sensor comprising: - a heating element, for heating a skin of the patient at the measuring site, - a control unit for controlling the temperature of the heating element, processing of the sensor signals, and controlling communication between the sensor and a monitor of the system for displaying the measured partial pressure of oxygen, - a heating element, for heating a skin of the patient at the measuring site, - a control unit for controlling the temperature of the heating element, processing of the sensor signals, and controlling communication between the sensor and a monitor of the system for displaying the measured partial pressure of oxygen, the control unit further being adapted to control the heating element to cycle the temperature of the skin at the measuring site between a lower and a higher temperature by: - adjusting and maintaining, by the controller and the heating element, the measuring site at a temperature close to body core temperature in a first time interval so that the skin temperature at the measuring site is maintained at the lower temperature, and - increasing and maintaining, by the controller and the heating element, the temperature at the measuring site in a second time interval so that the skin temperature at the measuring site is maintained at the higher temperature, which is at least 41 0 C, - adjusting and maintaining, by the controller and the heating element, the measuring site at a temperature close to body core temperature in a first time interval so that the skin temperature at the measuring site is maintained at the lower temperature, and - increasing and maintaining, by the controller and the heating element, the temperature at the measuring site in a second time interval so that the skin temperature at the measuring site is maintained at the higher temperature, which is at least 41 0 C, wherein the controller is configured so that the first time interval is longer than the second time interval; wherein the controller and the heating element are configured so that the sequence of first and second time intervals is repeated for performing the cycling of the temperature of the skin at the measuring site; wherein the system further comprises means for communicating between the sensor and the monitor; and wherein the system is further configured to: show measured levels at the monitor for points in time when the skin temperature is sufficient for reliable meausures; and show, at the monitor, extrapolated levels which are extrapolated from one or more of the measured levels for points in time when the skin temperature is such that the measures cannot be relied upon directly. show measured levels at the monitor for points in time when the skin temperature is sufficient for reliable meausures; and show, at the monitor, extrapolated levels which are extrapolated from one or more of the measured levels for points in time when the skin temperature is such that the measures cannot be relied upon directly.