20 T. Rath et al.: J Extra Corpor Technol 2026, 58, 19 – 31
enables investigators to understand the source of GME generation and explain the transmission observed in TCD studies. Investigators use these devices clinically to understand the air-trapping capabilities of various CPB disposables, such as oxygenators [ 9 ], venous bubble traps [ 10 ], and integrated versus non-integrated arterial line filters [ 11 ]. Others have used bubble counters to understand air entry associated with open vs. closed surgical procedures, perfusionist interventions, left ventricular venting, and surgical manipulation [ 12 – 14 ]. A benefit of measuring bubble activity in vivo is that results can be linked to neurologic testing. Doganci and colleagues demonstrated a positive correlation between intraoperative GME intensity and neurocognitive tests, suggesting that the level of GME may be a determinant of the psychological outcome after coronary artery bypass grafting with CPB [ 15 ].
The simultaneous use of ultrasonic bubble measuring devices attached to the CPB circuit and ultrasonic measurement of emboli in the cerebral arteries during surgery provides clinicians with a clearer picture of best practices in mitigating emboli during CPB. It can help develop quality improvement plans [ 16 ].
In vitro studies using ultrasonic bubble counters enable patient-independent examination of the air-handling capabilities of CPB circuit components and perfusion practices associated with increased GME. Controlled benchtop studies can minimize potential confounders associated with clinical studies and isolate the influence of variables such as air in the venous line / reservoir, air entering the cardiotomy suction ports, and the influence of the venous reservoir level.
Investigators have found that residual or entrained air in the venous cannula / line can be transmitted past the pump, oxygenator, and arterial filter [ 17 – 19 ]. Venous air is especially concerning when using vacuum-assisted venous drainage [ 20, 21 ]. Excessive cardiotomy suction or vent speed can also increase the number of bubbles transmitted to the arterial line. Mixing nitrogenous air with blood results in foam that can pass through the cardiotomy, pump, oxygenator, and arterial filter [ 22 – 25 ]. A lower reservoir level shortens the distance bubbles introduced into the venous line or cardiotomy reservoir must travel to exit and move into the arterial pump, and has been implicated in the ability of these disposables to remove air [ 26 ].
The ability to trap or remove air after it enters the cardiopulmonary bypass circuit is also vital, leading investigators to test the GME removal capability of oxygenators and arterial filters [ 27 – 30 ]. Recently, interest has focused on the efficacy of GME removal by arterial filters integrated into oxygenators [ 31 – 34 ].
The amount of GME a patient receives results from the combined impact of many variables. A recent paper elegantly described this using an in vitro circuit and ultrasonic bubble counter on the reservoir outlet to develop a neural networkbased modeling of the number of microbubbles associated with four circulation factors: suction flow rate, venous reservoir level, continuous blood viscosity, and perfusion flow rate [ 35 ]. They found the field suction flow rate to be the most predictive of anticipated GME activity, while perfusion blood flow was the least predictive, as measured post-reservoir. This group also developed a five-factor model examining how temperature changes can affect GME transmission [ 36 ].
Building on the work of these investigators, this project aims to develop an understanding of how the introduction and movement of GME in the cardiopulmonary bypass circuit are related to two modifiable interventions – suction flow rate and venous reservoir level. We aimed to isolate and explore the influence of these interventions using a state-of-the-art bubble counter, testing currently used perfusion disposable reservoirs and oxygenators / arterial filters from three different manufacturers. We hypothesize that the suction flow rate will be directly proportional to GME transmission, while the reservoir level will be inversely proportional, and we aim to guide safe threshold values for each.
Materials and methods Hardware
All trials were conducted using a four-pump base heart-lung machine( Stockert S3 Roller Pump with S3 Console 10-60-00, SORIN Group Deutschland GmbH, Müchen, Germany) with a Sorin Revolution centrifugal pump driver and ultrasonic flow probe( LivaNova, Mirandola, Italy) placed distal to the oxygenator. A 3T Heater / Cooler( LivaNova, Mirandola, Italy) was used to control temperature.
Circuit description
The in vitro, open, recirculating test circuit( Figure 1) is a modified version of a previous design [ 37 ] used in our laboratory to mimic adult perfusion. The first modification to this circuit was adding a Terumo CapioxÒ FX25 Advance venous reservoir( Terumo, Ann Arbor, MI, USA) to serve as a“ patient” reservoir. This functioned to minimize GME returning to the reservoir being evaluated via the venous line, allowing for independent control of level and volume in the“ test” reservoir using a Hoffman clamp. We found anecdotally that it was easier to de-air the circuit before experimentation if blood was directed to this“ patient” reservoir via the venous line. A second modification was adding a 1 / 4-inch sucker configuration to deliver a controlled mix of room air( 200 mL / min) and blood into the cardiotomy portion of the“ test” venous reservoir( Figure 1).
The arterial pump was a Sorin Revolution centrifugal pump( LivaNova, Mirandola, Italy) with a flow probe calibrated to zero before each trial. The roller pumps used for suction and air injection were set to 100 % occlusion. PVC tubing( 1 / 4, 3 / 8, 1 = 2 inch) was cut to the same standardized lengths for each experimental trial and connected with appropriate tubing connectors. Following the completion of each trial, all disposable components were discarded and replaced.
The coated“ test” reservoir and oxygenator with integrated arterial filter combinations trialed were as follows: Medtronic Affinity Fusion TM( n = 10)( Medtronic, Minneapolis, MN, USA), SORIN Inspire 8F( n = 9)( LivaNova, Mirandola, Italy), and CapioxÒ FX25 Advance( n = 6)( Terumo Cardiovascular, Ann Arbor, MI)( Table 1). The oxygenator manifold and arterial filter purge lines were opened during the trials, and the volume was returned to the test reservoir’ s cardiotomy.