Effects of standard unfractionated and low-molecular-weight heparins on platelets of patients undergoing total hip replacement surgery.

For prevention of venous thromboembolism in general and in orthopedic surgery, patients are treated prophylactically with standard unfractionated heparins (SH) or with low-molecular-weight heparins (LMWH). Patients (n = 22) undergoing total hip replacement surgery received either 5,000 IU SH (Heparin-Na) three times per day (n = 10 patients) or LMWH (Fraxiparin) once per day (n = 12 patients). Blood samples using CTAD (citrate, theophylline, adenine, dipyridamole) as anticoagulant were collected perioperatively after the first heparin administration, after the operation, and daily until day 4 postoperatively. After cooling at 4 degrees C blood samples were centrifuged, platelet-rich plasmas (PRPs) prepared, and after platelet counting PRPs were divided into platelet sediments (PS) and platelet-poor plasmas (PPP). Cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), serotonin, P-selectin, and laminin were analyzed in PPP and in PS after two freezing/thawing cycles. Platelet serotonin contents and serotonin release did not differ in either heparin group (SH and LMWH). In the LMWH group, 72 h postoperatively the intraplatelet cAMP was significantly (p < 0.01) higher. P-selectin values in PPP and platelet P-selectin release did not vary between the SH and the LMWH group; on the contrary, the platelet P-selectin content increased in the LMWH group 72 and 96 h postoperatively, while in the SH group this parameter showed a small decrease. The differences were significant (p < 0.05). The platelet-bound laminin underwent a slight change 48 and 72 h postoperatively in the LMWH group, but in the SH group the platelet-bound laminin increased permanently and significantly (p < 0.05; p < 0.01) until 72 h postoperatively, but 96 h postoperatively there was a small decline. In the SH group, 24-96 h postoperatively the platelet-bound laminin was significantly (p < 0.05; p < 0.005) augmented, compared with the LMWH group. The higher cAMP and P-selectin contents in the LMWH group suggest that platelets are less impaired by LMWH, and the augmented platelet-bound laminin in the SH group could express the platelet impairment evoked by standard unfractionated heparins.