CHAPTER 3 PERIOPERATIVE HEMATOLOGIC MANAGEMENT
KEY POINTS
Operative planning for high-risk vascular anomalies requires laboratory and/or imaging at least 2 weeks before surgery.
The best laboratory predictor of bleeding risk in patients with consumptive coagulopathy is a low fibrinogen level.
The best predictor of thrombotic risk is patent ectatic veins connecting to the deep venous system.
Consumptive coagulopathy can be normalized with anticoagulation and cryoprecipitate in most patients.
Interdisciplinary communication throughout the planning, surgery, and postoperative care is critical to achieve safe and effective surgical management of vascular anomalies.
Although there has been a recent emergence of medical therapies for a variety of vascular anomalies, procedural management remains central to the care of many of these disorders. This chapter will cover how to assess for bleeding and thrombotic complications and minimize these risks before, during, and after procedures. The combination of bleeding and thrombotic risk in the same patient requires expertise and vigilant, expectant management. Interdisciplinary discussion and coordination of perioperative care are critical to this process. In addition to surgical disciplines, anesthesia, hematology, blood bank, critical care, and interventional radiology can play critical roles.
FUNDAMENTALS OF HEMOSTASIS AND THROMBOSIS
Hemostasis and thrombosis involve three separate but intertwined biologic processes:
Slowed blood flow: Platelets are responsible for the initial adhesion to damaged tissues, and formation of the platelet plug initiates clot formation. This is particularly true for mucosal and cutaneous surfaces. Activated platelets can occur in vascular anomalies and can be predisposed to the initiation of thrombosis, especially around procedures and during inflammation.
Endothelial damage: Subendothelial tissue factor or foreign materials (for example, catheters) can initiate the coagulation cascade, an amplifying proteolytic series of events leading to activated circulating coagulation factors. This process culminates in fibrinogen cleavage by thrombin into fibrin, which is crosslinked and forms the fibrin clot. The conversion of soluble fibrinogen to a solid fibrin clot stops further bleeding and allows healing of the underlying injury.
Hypercoagulability: The balance of fibrin clot breakdown is controlled by plasmin, which proteolytically cleaves crosslinked fibrin, releasing D-dimers into the circulation and recanalizing the vessel. Fibrinolysis is understudied in vascular anomalies, but hypofibrinolytic states promote thrombosis, whereas hyperfibrinolytic states promote recurrent bleeding and poor wound healing. Hyperfibrinolysis is targeted by antifibrinolytic drugs, such as epsilon-aminocaproic acid or tranexamic acid; these agents are most effective for mucosal bleeding.
Each of these has relevance in vascular anomalies. Slowed blood flow is generally considered for periods of immobility, cardiac insufficiency, and vascular compression. In addition, for patients with vascular malformations, dilation (ectasia) of venous channels and saccular vascular structures creates areas of slowed, swirling, stagnant, or even reversed blood flow. Adequate blood flow is protective from thrombosis by diluting activated clotting factors. By allowing activated platelets and clotting factors to concentrate in areas of slowed blood flow, localized intravascular coagulopathy occurs in slow-flow vascular malformations. Studies comparing intralesional with systemic blood have demonstrated the concentration of coagulopathy within intralesional blood.
Endothelial damage generally refers to surgery, catheter placement, and trauma. Vascular anomalies are lined with abnormal endothelium, allowing exposure of subendothelial collagen and tissue factor and resultant activation of platelets and clotting factors. In healthy circulation, vascular endothelium is coated with antithrombotic proteins, including thrombomodulin and endothelial protein C receptor. The loss of these proteins and their endogenous anticoagulant properties also contributes to thrombotic risk. Furthermore, the main therapies for slow-flow vascular malformations are surgical resection and endovascular sclerotherapy, which trigger additional endothelial injury.
Hypercoagulability refers to the inherent properties of the blood favoring thrombosis. Common inherited causes are factor V Leiden and prothrombin gene mutation G20210A, which occur in 5% and 2% of whites, respectively. Deficiencies in anticoagulant proteins such as antithrombin, protein C, or protein S can be inherited or acquired in the setting of thrombosis. Inflammatory and rheumatologic disorders, especially those associated with antiphospholipid antibodies, are also prothrombotic. Specific laboratory assessment for hypercoagulability is not indicated for all patients with vascular anomalies but should be considered for patients with a family history of thrombosis or a personal history of thrombosis outside of the vascular malformation or severe extensive or recurrent thrombosis.
HEMATOLOGIC ABNORMALITIES IN VASCULAR ANOMALIES
There are two general types of coagulopathy in vascular anomalies:
Platelet trapping within vascular tumors
Intralesional thrombosis, leading to consumptive coagulopathy in vascular malformations
These are distinct processes occurring in different types of vascular anomalies.
Platelet trapping within vascular tumors is generally referred to as Kasabach-Merritt phenomenon. The classic vascular tumor associated with platelet trapping is kaposiform hemangioendothelioma (KHE), an infiltrative vascular tumor occurring mainly during infancy. This can also occur in tufted angioma, cutaneovisceral angiomatosis with thrombocytopenia, and kaposiform lymphangiomatosis. Alterations in coagulation testing can occur concurrently in severe cases. Although not proved in the literature, the leading hypothesis is that normal circulating platelets adhere to abnormal lymphatic endothelium. Rapid consumption of transfused platelets in the vascular tumor supports this hypothesis. On adherence, platelets are activated and begin to aggregate and form platelet-rich thrombi. These are visible on histologic findings in KHE. Activated platelets can also initiate fibrin clot formation, although this is secondary, in contrast to consumptive coagulopathy within slow-flow vascular malformations.
Thrombocytopenia can also occur in association with vascular anomalies for other reasons. Central hemorrhage into a large, hepatic, rapidly involuting congenital hemangioma can cause thrombocytopenia. Diffuse gastrointestinal bleeding or secondary hypersplenism from portal hypertension can also lead to mild-to-moderate thrombocytopenia. Massive venous ectasia with slow or stagnant blood flow has also been associated with mild thrombocytopenia and thrombotic risk. Slow-flow venous malformations are at risk of consumptive coagulopathy. This is most common in extensive cases, especially those of pure venous malformation or venolymphatic malformation (blue rubber bleb nevus syndrome). Other mixed-type vascular anomalies with slow blood circulation are also at risk. Activation of the clotting cascade by exposure to abnormal vascular endothelium and subendothelial proteins triggers this process, which is concentrated in a slow-flow environment. In mild cases, aspirin may modulate symptomatic thrombophlebitis. Periprocedurally and in more severe cases, aspirin is insufficient, and anticoagulation is indicated to suppress intralesional thrombin generation and thrombosis. Consumptive coagulopathy may refer to D-dimer elevation, prolonged prothrombin time (PT) or activated partial thromboplastin time (aPTT), or a deficiency of fibrinogen. Low fibrinogen is predictive of bleeding risk and is corrected with anticoagulation and/or cryoprecipitate. If PT/aPTT prolongation remains after fibrinogen correction, further hematologic workup is recommended.
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