A crucial component of ECMO circuits are the flow sensors. At minimum, they provide measurement of blood flow rate and bubble detection. Newer sensors can also estimate hematocrit and oxygen saturation. The flow sensor is incorporated into the downstream side of the centrifugal pump. An additional clip-on sensor is sometimes included downstream of the oxygenator. In more advanced compact systems such as the Maquet CARDIOHELP, the sensors are built into the pump/oxygenator disposable component.

ECMO Ultrasonic Flow Bubble Sensor

Blood Flow Sensor

With positive displacement pumps, the blood flow flux through the pump is determined solely by the pump speed. However, with centrifugal flow pumps that rotate at set speeds, the flow rate through the pump also depends on the upstream and downstream pressures. Therefore, an external sensor is required to provide the blood flow rate information.

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The sensors work by by measuring the transit-time of ultrasonic pulses through the blood flow. The flow sensor surrounds the ECMO circuit tubing. Ultrasonic impulses are sent from one piezo crystal to another (either directly in an X-pattern or by a reflector with the crystals acting alternately as transmitters and