von Willebrand Factor and Platelet Count in Ruptured Abdominal Aortic Aneurysm Repair

AbstractObjective: von Willebrand factor (vWF) is essential for the formation of platelet aggregates at sites of vascular endothelial cell (EC) injury. Peri-operative thrombocytopenia is associated with poor outcome in ruptured abdominal aortic aneurysm (AAA) repair. This prospective study examines the relationship between vWF and platelet count (PC) in ruptured AAA repair.Methods: plasma vWF antigen, PC and C-reactive protein (CRP) were measured pre-operatively, and immediately before and 5 min after aortic clamp release, and on post-operative days 1 and 2 in 20 patients (18 men and 2 women of median age 74, range 63–86, years) with ruptured AAA.Results: elevated vWF was present in 13 (65%) patients pre-operatively, and 14 of 16 (88%) survivors at 24 h post-operatively. All patients demonstrated an intra-operative fall in vWF. There was no significant difference in vWF levels between survivors and non-survivors. PC was below the normal range in 8 (40%) patients pre-operatively and all patients at 24 h. Eighteen (90%) patients demonstrated an intro-operative fall in PC. PC was significantly lower in non-survivors pre-operatively (p=0.007), immediately before (p=0.009) and 5 min (p=0.009) and 24 h (p=0.02) after clamp release. There was a significant positive correlation between vWF and PC pre-operatively (r=+0.48, p=0.033), and immediately before (r=+0.47, p=0.044) and 5 min after clamp release (r=+0.5, p=0.043). There was a significant positive correlation between peak vWF level and the greatest fall in PC (r=+0.65, p=0.006). There was a significant negative correlation between vWF and CRP and operative blood loss; and between PC and CRP, operative blood loss and aortic clamp time.Conclusions: these data demonstrate that EC activation, the acute phase protein response, operative blood loss and aortic clamp time all contribute to the peri-operative fall in PC in patients with ruptured AAA. The peri-operative fall in circulating levels of vWF and PC may represent consumption secondary to macro- and microvascular thrombus formation. The resultant procoagulant state may partly explain the association between low PC and poor outcome in ruptured AAA