A fluid flow sensing apparatus and method for detecting pressure and the presence of bubbles within a fluid tube. The flow sensor comprises a housing configured to receive a portion of the tube and to house the pressure sensor and the ultrasonic transmitter. The pressure sensor is positioned adjacent the tube and is configured to receive a pressure sensor signal, which correlates to a detected pressure differential within the tube. An internal controller transmits a drive signal to the ultrasonic transmitter, which emits ultrasonic waves through a portion of the tube and to the pressure sensor. The pressure sensor receives both the ultrasonic waves and a pressure sensor signal, and subsequently transmits an output signal to the internal controller. In the presence of a pressure differential or a bubble within the tube, the output signal will exhibit a DC shift or a distortion of its signal characteristics, respectively.
