The invention provides a multi-sensor system for monitoring a patient's respiratory rate. The system features an impedance pneumography sensor featuring at least two electrodes and a processing circuit configured to measure an impedance pneumography signal and a 3 axis accelerometer) that attaches to the patient's torso and measures an ACC signal indicating movement of the chest or abdomen that is also sensitive to respiratory rate. The signals are collectively processed, e.g. with the adaptive filter to determine a value for the respiratory rate.