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A preliminary investigation into the use of the cavitation number equation to predict emboli formation in the cardiopulmonary bypass circuit / Thomas J. Grulkowski.

by Grulkowski, Thomas J.

Cardiopulmonary bypass -- Adverse effects

Extracorporeal Circulation

Venous pressure

94 leaves : ill. ; 28 cm.

Advisor: Dr. Ronald Gerrits

Committee members: Dr. Larry Fennigkoh, Dr. Charles Tritt

Introduction -- Background -- Methods and materials -- Statistical analysis -- Results -- Discussion Appendix A) Trial order B) Raw blood gas data C) Three-way ANOVA repeated measures results D) Tukey multiply comparison test.

Purpose: In this preliminary investigation the cavitation number equation was used as a model if it could accurately predict bubble formation in a cardiopulmonary bypass (CPB) circuit while using porcine blood. There are many documented sources of gaseous emboli production within the CPB circuit, but this current study focuses on cavitation. Cavitation is the pulling of gas out of solution due to pressure gradients within a liquid. Based on this equation, it was predicted that a larger amount of bubbles would be produced at higher flow rates and as the vacuum pressure becomes more negative.

Methods and Materials: A standardized model of an adult CPB circuit was utilized. Two flow rates were tested, 3.5 L/min and 5.5 L/min, along with four vacuum pressures, (0, -25, -50, -75 mmHg). These were chosen due to the wide range of cavitation numbers they represented. The cavitation number is a dimensionless number, the higher the number the less likely bubbles will be produced and the lower the number the more likely bubbles are to be produced. There wee four sites on the circuit where bubble formation was recorded; they were the venous line, pump inlet, pump outlet, and post arterial filter. Ten trials were conducted for each flow rate, vacuum pressure, and circuit location, while recording the bubble formation with a Doppler ultrasound bubble detector.

Results: A three way ANOVA repeated measures design was used to evaluate the velocity, vacuum pressure, and circuit locations. When comparing the two flow rates there was a significant increase in bubble formation at 3.5 L/min. When comparing the four vacuum pressures, there was a significant increase in bubble formation at -75 mmHg. When comparing the four circuit locations, there was a significant increase in bubble formation at the pump inlet. There are other significant data, but more importantly there is a trend in the mean bubbles produced to the cavitation number in the 5.5 L/min group at all four circuit locations, while this trend is less clear at the 3.5 L/min group. In conclusion the cavitation number can be used as a general guide in bubble formation but to predict an actual number is too difficult from this data at this time.

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