Effect of dextran and enoxaparin on early ePTFE graft thrombogenicity in sheep.

Objectives: To evaluate the effect of low molecular weight heparin (LMWH), dextran 70 and their combination on platelet adhesion and fibrinogen uptake in ePTFE grafts in an experimental sheep model.

Design: Prospective open study.

Setting: Animal Laboratory of a University Hospital.

Materials: Early thrombogenicity of ePTFE grafts was studied after interposition in the two common carotid arteries of 40 adult sheep. The animals received one of four different treatment regimens in a double blind randomised way: enoxaparin and polygeline, saline and dextran 70, enoxaparin and dextran 70 or saline and polygeline (control). The substances were administered i.v. with a total dose of 73 antifactor-Xa U/kg for enoxaparin and 1.0 g/kg for dextran 70. Polygeline and saline were used as placebo substances in equivalent volumes. On one side (random allocation) the carotid blood flow was restricted to 25 ml/min, on the other side it was left unrestricted.

Chief Outcome Measures: The following variables were studied: 1) fibrinogen uptake; 2) platelet uptake; 3) early graft patency; 4) blood flow in patient grafts; 5) visible presence of graft thrombus; 6) thrombus weight.

Main Results: The results verified the importance of adequate blood flow as only 30% of grafts with restricted blood flow in the control group were patent compared with 80% of those with unrestricted blood flow (p = 0.038). Dextran 70, enoxaparin and the combination of the two increased early graft patency (p < 0.05) and reduced thrombus weights (p < 0.05) in grafts with restricted blood flow. The relative number of grafts with thrombus free surface was increased in the unrestricted blood flow situation.

Conclusions: Dextran 70 and enoxaparin appeared to be equally effective in decreasing fibrinogen and platelet uptake in the grafts. Their combination was not significantly more effective although there was a favourable trend.