Background: Minimizing Gaseous microemboli (GME) introduced into the CPB circuit can help alleviate neurologic injury. This study focuses on understanding how suction flow rate and the reservoir level can influence the introduction of GME past the venous reservoir during CPB. 

Methods: An in vitro mock CPB loop filled with bovine blood was used to simulate adult CPB. A Gampt BCC-300 bubble detector measured bubble size, volume, and count at three locations: post-reservoir (venous), post-oxygenator/arterial filter (arterial), and the venous inlet to the reservoir (recirculation). Room air was added into the suction line at 200 mL/min and mixed with blood to simulate aerated suction return. Bubble transmission was measured for three minutes at three reservoir levels, 200 mL, 500 mL, and 1000 mL, and at four pump sucker flow rates: 25 RPM (0.32 L/min), 50 RPM (0.65 L/min), 75 RPM (0.99 L/min), and 100 RPM (1.32 L/min). GME count data were pooled from three commonly used, coated, disposable reservoirs/oxygenator combinations: Medtronic Affinity Fusion, Terumo CAPIOX FX25, and Sorin Inspire 8F. 

Results: A total of 284 measurements were conducted, and the data from all reservoir manufacturers were analyzed and averaged. A statistically significant interaction was noticed between roller pump suction rate and reservoir level (p-value < 0.0001) at the venous sensor. As the suction flow rate increased, the reservoir level decreased, or a combination of the two occurred, a significant increase in GME count was observed at the post-reservoir sensor. Analysis of the GME count from the post-oxygenator/filter sensor revealed a significant increase as the suction flow rate increased from 25 RPM to 100 RPM. 

Conclusion: A minimum effective suction flow rate and maximum practical reservoir level are recommended to prevent the transmission of GME through the cardiopulmonary bypass circuit and potentially to the patient. Care should be taken to continuously monitor these variables throughout the case and adjust them accordingly.