Vascular surgery is often needed to salvage an ischemic limb threatened by HIT-associated acute arterial thromboembolism involving large arteries (Sobel et al., 1988). When performing vascular surgery during acute HIT, it is appropriate to maintain anticoagulation at least in the lower therapeutic range, if possible, before, during, and after surgery, until platelet count recovery. In patients with latent HIT (i.e., no longer thrombocytopenic, but with clinically significant levels of HIT antibodies still present), the intensity of anticoagulation depends on the perceived risk of vessel (or graft) occlusion. In patients at high risk of occlusion (e.g., surgery involving below-knee vessels), the patient should be therapeutically anticoagulated before vessel clamping (in addition to receiving intraoperative flushes with anticoagulant), with therapeutic anticoagulation maintained for several days after surgery. In surgery involving larger vessels, the use of intraoperative flushes alone, followed by postoperative prophylactic-dose anticoagulation, might be sufficient.
Either danaparoid or lepirudin can provide intraoperative anticoagulation. One author (AG) uses one of the following solutions to flush the vessel postembo-lectomy: (1) lepirudin, 0.1 mg/mL saline (one 20 mg ampule in 200 mL saline), using up to 250 mL in a normal-weight patient, and assessing the aPTT before giving more lepirudin to avoid overdosage (the lepirudin flushes thus can achieve therapeutic intraoperative anticoagulation; see Chapter 14); (2) danaparoid, 3 anti-Xa U/mL (one 750 U ampule in 250 mL saline), using up to 50 mL in a normal-weight patient (this small flush dose is used because systemic anticoagulation is achieved by giving a 2250 U bolus of danaparoid preoperatively (see Chapter 13).
Recommendation. Surgical thromboembolectomy is an appropriate adjunctive treatment for selected patients with limb-threatening large-vessel arterial thromboembolism. Thrombocytopenia is not a contraindication to surgery. An alternative anticoagulant to heparin should be used for intraoperative anticoagulation (grade 1C).
In contrast to large artery thrombosis, a surgical role for severe venous or microvascular limb ischemia is less certain (Warkentin, 2007). Fasciotomy is sometimes performed in patients with severe venous limb ischemia and suspected compartment syndrome, but this procedure may delay or interrupt much-needed anticoagulation. Further, it is uncertain to what extent compartment syndromes contribute to limb ischemia/necrosis in patients with HIT-associated DVT and associated microvascular thrombosis, including those related to severe disseminated intravascular coagulation (DIC) and/or coumarin-induced protein C depletion. In our view, therapy should focus on intensive medical therapy, including aggressive anticoagulation and (when appropriate) reversal of coumarin anticoagulation with iv vitamin K.
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