Incidence in USA: 1:2000-5000 (may be higher)

Men and women equally affected and no racial or ethnic difference

Risk of postop thromboembolic phenomena; 40% to 70%, most common (in descending order): DVT, pulm embolus, mesenteric thrombosis, cerebral venous, and retinal thrombosis; highest risk in those with antithrombin III (AT III) levels <50% of normal

Risk of pregnancy-related venous thromboembolism may be >50% in untreated pts

Heparin resistance is common

Risk of postop thromboembolic phenomena; 40% to 70%, most common (in descending order): DVT, pulm embolus, mesenteric thrombosis, cerebral venous, and retinal thrombosis; highest risk in those with antithrombin III (AT III) levels <50% of normal

Risk of pregnancy-related venous thromboembolism may be >50% in untreated pts

Heparin resistance is common

Hypercoagulable state periop

Thrombus formation on indwelling cath

Pulm emboli or DVT with immobility

Mesenteric, inferior vena cava, or CNS thrombosis

Withdrawal of warfarin sodium preop, as pts may be heparin resistant

Timing of neuraxial anesthesia in anticoagulated pts

AT III is an α ₂ -globulin and a serine protease inhibitor, capable of inactivation of thrombin and factor Xa in blood.

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  It has antiinflammatory properties via interactions with the endothelium.

  
  
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  AT III deficiency results in an unusual susceptibility to thromboembolic disease.

Heparin resistance may be problematic during surgery.

Massive thromboembolism can occur periop with AT III levels <50.

Genetic: Reduced AT III synthesis inherited as an autosomal dominant trait, manifests as thromboembolism in late teens to early 30s

Acquired: Secondary to consumption of AT III due to massive thromboembolic disease, DIC, renal disease with proteinuria (especially nephrotic syndrome), chronic liver disease, prolonged heparin therapy, and increased protein catabolism

Conflicting data about role of oral contraceptive use, pregnancy, and CAD