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The effects of clamping the outlet of two different centrifugal pumps on platelet function / George G. Watts.

by Watts, George G.

Cardiopulmonary bypass -- Adverse effects

Centrifugal pumps

Blood Platelets

Blood Coagulation.

Stress, Mechanical

49 leaves : ill. ; 29 cm.

Thesis advisor: Dr. Jeffrey LaMack.

Committee members: Dr. Ronald Gerrits, Shannon Voborsky.

Introduction -- Background -- Hypothesis -- Materials and methods -- Results -- Discussion -- References -- A: Three-way ANOVA SigmaStat report for percent platelet inhibition -- B: Multiple linear regression SigmaStat report for percent platelet inhibition -- C: One-way ANOVA SigmaStat report for baseline platelet count -- D: Raw data.

One of the most important components of hemostasis is the function and efficacy of platelets. They are responsible for being one of the first response mechanisms to tissue injury and they also activate the coagulation and wound healing responses. Cardiopulmonary bypass (CPB) is well known to have an adverse effect on platelet function and number, yet is a necessary component for most cardiac surgical procedures. One possible cause of platelet dysfunction during CPB is platelet damage caused by the shear stress generated by centrifugal pump heads. Shear stress has a notable effect on platelet function both in terms of irreversible aggregation and complete lysis. Shear stress is generated at different locations within centrifugal pumps, depending on the pump design.

Every surgery involving CPB eventually involves weaning of the patient off of the extracorporeal pump. In a circuit that uses a centrifugal pump, this requires eventually shutting off forward flow (and also backflow) to the patient by placing a clamp distal to the pump head. The non-occlusive nature of the pumps require a clamp be in place, and from there, the perfusionist will fill the patient with whatever volume remains in their circuit depending on the current patient hemodynamics. The practice of many perfusionists is to leave the centrifugal pump running at a speed high enough to still overcome the resistance posted by the patient. With the clamp in place, this will result in high pressures and shear forces on the blood within the pump head. The goal of this novel study was to determine a correlation between pump speed, the time that the outflow of the pump is clamped, the pump design and the resultant level of platelet activation due to each factor.

A total of 24 trials were performed in which bovine blood was circulated through miniature mock CPB circuits. A Bio-Medicus Biopump BP-80 and a Sarns 7850 centrifugal pump were used with two different levels of clamp time and pump speed. The levels of time were chosen to be 30 seconds and 5 minutes, and the speeds were correlated for each pump to a flow rate of 6.15 LPM and 12.9 LPM in this minimal resistance circuit. The Plateletworks platelet function assay, with collagen as an agonist, was used to determine levels of platelet activation. All statistical analyses were performed with a level of significance at p<0.05.

There was a positive correlation found with the Biopump, increased clamp time, and increased pump speed with an increase in platelet inhibition. However, the findings were not statistically significant and had a low statistical power associated with the analyses. Considering that this was a novel study, it was encouraging to see the expected correlation despite a lack of statistical significance. Further study should be performed to determine a statistically significant association between the variables.

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