An ultrasonic sensor is attached to the body to detect flow in a blood vessel. Signals from the sensor are processed to produce measures of flow during the administration of CPR such as flow velocity and flow pulsatility. The flow measures are compared with flow characteristics desirable during CPR and the result used to produce audible instructions guiding a caregiver in the administration of CPR. The flow measures may be used in conjunction with other detected physiological parameters such as compression force or depth, chest impedance, blood pressure, and ECG data to guide CPR.
