Flow-Bubble Sensors applied to Heart-Lung-Machines

SONOFLOW CO.56 Pro - simply mounted hangingSONOFLOW CO.56 Pro - light weighted and mounted hanging
SONOFLOW CO.56 Pro - simply mounted hangingSONOFLOW CO.56 Pro - light weighted and mounted hanging


  • Non-invasive SONOFLOW CO.56 FlowBubble sensors applied to heart-lung-machines
  • Identifying air bubbles in the arterial line to guarantee active patient safety
  • Continuous flow rate monitoring of the arterial pump
  • Operating up to twelve independent sensors with only one control unit guarantees the world’s smallest footprint for an OEM flow- and bubble detector

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, however, is often also named as heart-lung machine (HLM). As these machines deal with human lives, technical requirements are specifically high. A reliable operation of all utilized equipment must be guaranteed at any time. For that reason, combining flow measurement and air bubble detection is said to be a significant safety and comfort feature.

Hybrid SONOFLOW CO.56 Flow-Bubble sensor series successfully designed into heart-lung machines

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 patients's heart drained into the venous reservoir, where it is processed and smoothly pumped back into the aorta of the human body.

A medical device full of high-grade technologies

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 substitute for human lungs by delivering oxygen to, and extracting carbon dioxide from venous blood. The tubing system of the heart-lung machine consist of PVC and silicone tubes, cannulas and shunts which are used in different tubing sizes. The heart of a 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.

Different sensors monitor, support and protect vital human functions

Bubble detectors are key to patient safety. They need to be necessarily clamped on the arterial line right after the arterial filter to protect against massive air embolism. The bubble sensors automatically warn and cut-out the arterial pump. However, there are further options to place bubble detectors within the HLM circuit. As the venous reservoir will be the first and most likely place where air is introduced into the circuit, subsequent the venous reservoir is thus an optional place to apply a bubble sensor to get the air out before the arterial filter. Even to place a bubble sensor between 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.SONOFLOW CO.56 FlowBubble Sensor in Heart-Lung-Machines

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 are used to do this job failure-free and reliably.

Hybrid SONOFLOW CO.56 ultrasonic sensor series combining flow measurement and air bubble detection

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 the option to operate up to twelve independent sensors with only one control unit guarantees the world’s smallest footprint for an OEM flow- and bubble detector to be used in HLMs. The non-invasive ultrasonic sensors operate without any media contact, 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 of about one percent, depending on where the sensor has been mounted and which kind of liquid is being measured. Simultaneously to measuring flow conditions, the sensor is able to detect air bubbles as small as one third of the inner diameter of the tube.

SONOFLOW CO.56 successfully designed into heart-lung machines

Top medtec 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 leading companies developing and manufacturing HLMs has integrated the hybrid sensor solution into their recently launched devices.

SONOFLOW CO.56 Pro – Product Features at a Glance 
Compact sensor design with onboard electronics and data processing
Clamp-on solution for non-invasive measurement
Fast & bi-directional flow measurement
Measurement accuracy up to +/- 2% and repeatability of +/- 1%
(depending on where the sensor has been mounted and which kind of liquid is being measured)
Detection of bubbles as small as 30% - 50% of the inner tube diameter
Available for a wide range of tubing sizes and materials
SONOTEC is ISO 9001 and ISO 13485 certified

The main aspect of the manufacturer to trust in the SONOFLOW CO.56 sensor series is its small electronic footprint and its option for multipoint measurement. Thus, five of the smart sensors with different tubing channels have been easily applied to the customers’ newly developed console. The onboard electronics and its option for data processing make connecting the sensors an easy game. The built-in microcontroller guarantees to control all processes whose data is transferred via RS485-interface. The sensors themselves operate to measure flow rates on different tubes and shunts going to the body or back into the venous circuit of the heart-lung-machines and simultaneously 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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