A defibrillator 1 for determining a CPR compression rate, comprises electrodes 3 adapted for attachment to a subject, an impedance signal measurement system 5 which measures at least one impedance signal via the electrodes and an electrocardiogram (ECG) signal measurement system 7 configured to measure at least one ECG signal of the subject via the electrodes. The impedance signal is processed by an impedance signal processing system 9 (connected to the impedance signal measurement system) to obtain a plurality of impedance signal compression estimates and features and the ECG signal is processed by an ECG signal processing system 11 (connected to the ECG signal measurement system) to obtain a plurality of ECG signal features 18. A compression rate estimate processing system 13, connected to the impedance and ECG signal measurement systems, applies a plurality of criteria in association with compliance or non-compliance to the impedance and ECG signal features to select one of the plurality of impedance signal compression rate estimates as the cardiopulmonary resuscitation compression rate . An output unit 15 connected to the compression rate estimate processing system provides output feedback based on the cardiopulmonary resuscitation compression rate to a user of the defibrillator.
