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The effect of heat on the generation of gaseous microemboli in a centrifugal pump head : a thesis submitted to the faculty of the Milwaukee School of Engineering in partial fulfillment of the requirements for the degree of Master of Science in Perfusion / by Benjamin Buckoski.

by Buckoski, Benjamin., Milwaukee School of Engineering

Centrifugal pumps

Blood -- Circulation, Artificial

Heat -- Side effects.

Cardiopulmonary bypass -- Adverse effects

60 leaves : illustrations, some of which are in color ; 29 cm.

Thesis advisor: Dr. Jeffrey LaMack.

Committee members: Dr. Larry Fennigkoh, Kirsten Kallies.

Introduction -- Background -- Types of CPB arterial pumps -- Gaseous microemboli -- Cavitation -- Hypothesis -- Methods -- Experimental setup -- Results -- Discussion -- Recommendations -- References -- Appendix A: Data and analysis.

The delivery of microscopic quantities of air is an inevitable consequence of surgery incorporating the use of cardiopulmonary bypass (CPB). Gaseous microemboli (GME) may be room air which has infiltrated the circuit, or it can be generated in the blood through cavitation. GME are believed to be a contributing factor to the cognitive decline seen in patients who have undergone CPB. In order to minimize injury to the patient, it is important for a perfusionist to understand the relationship between their interventions during CPB and the generation of gaseous microemboli. Centrifugal pumps are commonly used to produce the arterial flow in CPB. Centrifugal pumps are afterload dependent, and therefore their outlet may be clamped to cease flow. The purpose of this study is to investigate the generation of heat and GME in an occluded Terumo Delphin centrifugal pump head at various pump speeds, initial fluid temperatures, and occlusion times.

A CPB circuit was created which incorporated EDAC (emboli detection and classification) GME sensors to quantify the amount of air generated by the centrifugal pump head, as well as a temperature probe to monitor the temperature of the fluid inside of the pump head. The circuit was primed with an aqueous glycerol solution to mimic the viscosity of blood at a hematocrit of 25%. The pump head was occluded for periods of 0, 5, 10, and 15 minutes at speeds of 1000, 1800, and 2600 RPM when the initial fluid temperature was 280, and 360C. The temperature of the fluid inside of the pump head was measured throughout the occlusion period, and upon removal of the clamp, the GME exiting the centrifugal pump head was measured for a period of one minute.

The results of this study showed the effect of pump speed and occlusion time on both the volume of GME generation and a change in pump head temperature. Time and the interaction between time and speed had a statistically significant effect on the change in temperature while the pump was occluded. The volume of GME produced at a pump speed of 2600 RPMs was much larger than at the other two pump speeds. Pump speed was found to have a statistically significant effect on GME volume, while occlusion time did not have a significant effect. The initial temperature of the fluid was not found to have a statistically significant effect on GME production. In practice, both centrifugal pump speed and occlusion times are under the control of the perfusionist. A greater understanding of the contribution of these factors to GME and heat generation offers the perfusionist insight into ways in which they may modify their practice to improve patient outcomes.

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