Correlation between preoperative platelet levels and heparin response
© Current Science Ltd 1999
Received: 26 November 1999
Published: 23 December 1999
Identification of factors responsible for the development of reduced sensitivity to heparin have important implications for cardiac surgery with cardiopulmonary bypass, because inadequate anticoagulation during this procedure can have profound thrombotic and haemorrhagic consequences. Recently, it was noted [1,2] that preoperative platelet levels are higher in heparin-resistant patients than in those who are heparin sensitive. In the present study, a possible relationship between preoperative platelet levels and heparin response was investigated.
Materials and methods
After local regional ethics committee approval and patients' informed consent was obtained, 87 patients undergoing either coronary artery bypass surgery (n = 73), valvular surgery (n = 8) or a combination of both (n = 6) were studied. Both preoperative platelet count and the heparin dose response (HDR) [measured using the Hepcon Hemostasis Management System (Medtronic, USA)] were determined for each patient. Patients with an HDR slope of 80 s/unit heparin per ml of blood or less were considered to have a reduced heparin sensitivity and were studied further. Heparin administration was standardized in all patients and coagulation status was determined by measuring the activated clotting time (ACT). If an ACT of 480s or greater was not achieved after administration of 300U/kg heparin, then a further 100U/kg was given. Patients were considered heparin resistant if the ACT was 480s or less after the second heparin dose. Patient data were compared using the Mann-Whitney U-test with results expressed as median (interquartile range) where appropriate. Correlation analysis was by Spearman's rank sum correlation.
From the original 87 patients, 30 had an HDR slope of greater than 80 s/U per ml (group 1). From the remaining 57 patients, 42 had an ACT of 480 s or greater after the first heparin dose (group 2), eight had an ACT of 480 s or greater after the additional heparin dose (group 3) and seven were considered to be heparin resistant (group 4). A significant correlation was measured between preoperative platelet levels and a reduced sensitivity to heparin (measured by the HDR slope; P < 0.001). No correlation with preoperative platelet levels was determined for either the baseline ACT or the ACT after the first heparin dose. Preoperative platelet count was shown to be significantly higher in groups 3 [252 (221–270) × 109/l) and 4 [262 (222–314) × 109/l), compared with 194 (165–223) × 109/l in group 1 (P < 0.05).
Preoperative platelet levels have been shown to correlate with a reduced sensitivity to heparin. This can probably be explained by the fact that patients with a higher platelet count have a greater capacity to produce platelet factor-4, which is released when platelet aggregation takes place. This mediator has a heparin neutralizing effect. We conclude therefore that assessment of preoperative platelet levels might be a useful diagnostic tool in identifying patients who have a reduced sensitivity to heparin.