5-year incidence of thrombocytosis and the effect on heparin dose response and heparin requirements

Thrombocytosis has been shown to be associated with heparin resistance. Contact activation of platelets results in release of Platelet Factor 4 from alpha granules present in the platelet cytoplasm. Platelet Factor 4 is a cationic substance that neutralizes heparin. This could result in inadequate heparinization during cardiopulmonary bypass (CPB). Inability to adequately anticoagulate patients with thrombocytosis could result in a poor clinical outcome. A retrospective review of pump records from 1991 to 1996 was used to assess the frequency of thrombocytosis, describe the demographic characteristics of patients with thrombocytosis, and determine the effects on patient heparin dose response (HDR) and additional heparin requirements. A platelet count of 400,000/mm3 was chosen as a cut-off for thrombocytosis. Of the 3281 patients undergoing CPB during this time period, a total of 571 patients were included in this review: 99 had high platelet counts. The over-all prevalence of thrombocytosis during this time period was 3.0%. Patients with thrombocytosis tended to be younger (p = .02), have lower preoperative HCT (p < .001), and weigh less (p < .001). These patients had lower post-heparin loading dose ACTs, lower HDR, required more additional heparin to reach an ACT of 480 sec before CPB, and required more heparin on CPB to maintain the ACT > 480 sec (p < .05). Multiple linear regression was performed and concluded that age, use of NTG and heparin drip preoperatively, and platelet count were significant predictors of the heparin dose response. Use of plasmapheresis to remove platelet-rich plasma (PRP) before CPB was performed in 22 patients, six of whom had high platelet counts. In these patients, removal of PRP resulted in no difference in the amount of additional heparin required pre-CPB to reach an ACT of 480 sec. (p = NS) Additional studies are needed to determine whether use of plasmapheresis is a cost-effective and clinically useful option in patients with thrombocytosis.