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Cardiopulmonary bypass (CPB) is a method that temporarily takes over the function of the heart and lungs during surgery, maintaining the human blood and oxygen circulation. The CPB pump, often also named as heart-lung machine (HLM), deals with human lives. Hence, technical requirements are specifically high. A reliable operation of all utilized equipment must be guaranteed at all times. For that reason, combining flow measurement and air bubble detection constitutes a significant safety and comfort feature.
As the heart-lung machine takes over the function of the heart and the lungs, it technically imitates the heart as a „pump“ and the gas exchange of the lungs. The HLM operates two main circuits: the venous circuit and the arterial circuit with additional feed lines. The venous circuit is fed by venous blood originating from the right ventricle of the patient’s heart drained into the venous reservoir, where it is processed and smoothly pumped back into the aorta of the human body.
The arterial pump takes over the full or partial pumping performance of the heart when required. The pump, which is fed by the venous reservoir and directly connected to an extracorporeal oxygenator, is the main pump of the HLM; all other pumps and components of the HLM are subordinated to it. All stored alarms regulate or stop the main pump and its associated components if required.
The extracorporeal oxygenator is an artificial device that substitutes for human lungs by delivering oxygen to, and extracting carbon dioxide from, venous blood. The tubing system of the heart-lung machine consists of PVC and silicone tubes, cannulas, and shunts which are used in different sizes. The heart of an HLM, however, is the console with integrated control unit and emergency batteries. Heart-lung machines are available as modular systems that each hospital can assemble according to its specific requirements and needs.
Bubble detectors are key to patient safety. They are required to be clamped on the arterial line right after the arterial filter to protect against massive air embolism. The bubble sensors automatically warn and deactivate the arterial pump. However, there are further options to place bubble detectors within the HLM circuit. The venous reservoir represents the first critical position where air can get into the circuit. Therefore, a reasonable location to apply the bubble sensor is between the venous reservoir and the arterial pump. Even to place a bubble sensor between the oxygenator and arterial line filter allows for trapping and purging air if necessary. The ideal and safest set-up would be to have multiple bubble sensors.
Flow sensors are also a main component in HLM’s. In order to not only detect air bubbles but also to effectively manage them, using shunts to connect the arterial circuit line and the venous reservoir in the tubing set-up is a critical point. When air is detected, the arterial line is promptly closed by the arterio-venous shunt while the detected air is directly eliminated to the venous reservoir. When no more air is spotted, the shunt automatically re-opens the tubing to again feed the arterial line going straight into the human body. For this reason, flow rates passing the shunt need to be continuously compared to the flows generated by the arterial pump, monitored and controlled over the time the HLM is running. Ultrasonic flow sensors accomplish this task failure-free and reliably.
As both bubble detectors and flow sensors are elementary safety elements in heart-lung machines, SONOTEC® has developed the SONOFLOW® CO.56 Pro ultrasonic sensor series, which combines both flow measurement and air bubble detection of liquids in one compact unit. The integrated electronics and option to operate up to twelve independent sensors with only one control unit guarantees the world’s smallest footprint for an customized flow and bubble detector to be used in HLMs. The non-invasive ultrasonic sensors operate without any media contact, they quickly perform bi-directional flow readings, and can be easily clamped free-hanging on the tubing.
The accuracy of the SONOFLOW® CO.56 Pro is up to two percent and the repeatability is as low as one percent, depending on where the sensor is mounted and which kind of liquid is actually measured. In addition to the measurement of flow conditions, the sensor is able to detect air bubbles as small as one third of the inner diameter of the tube.
Top medtech companies already rely on this game-changing technology and have implemented the control and monitoring unit for instantaneous flow and bubble detection into their equipment. One of the industry‘s leading companies developing and manufacturing HLMs has integrated the hybrid sensor solution into its recently launched device.
The main reason for the manufacturer to trust in the SONOFLOW® CO.56 Pro sensor series is the small electronic footprint and the option for multipoint measurement: Five of the smart sensors with different tubing channels have been applied to the customer‘s newly developed console. The onboard electronics and its options for data processing make connecting the sensors an easy game. The built-in microcontroller guarantees to control all processes while data is transferred via the RS485-interface. The sensors themselves measure flow rates on different tubes and shunts leading to the body or back into the venous circuit of the heart-lungmachine. Simultaneously, they detect air bubbles accidentally caused. Finally, the non-invasive ultrasonic sensors give feedback on the real flow compared to the theoretical flow of the pump.
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