Chapter 059. Bleeding and Thrombosis (Part 7)

The most important point in a history related to venous thrombosis is whether the thrombotic event was idiopathic (meaning there was no clear precipitating factor) or was a precipitated event. In patients without underlying malignancy, having an idiopathic event is the strongest predictor of recurrence of venous thromboembolism. In patients who have a vague history of thrombosis, a history of being treated with warfarin suggests a past DVT. Age is an important risk factor for venous thrombosis; the risk of DVT increases per decade, with an approximate incidence of 1/100,000 per year in early childhood to 1/200 per year...
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Chapter 059. Bleeding and Thrombosis (Part 7) Chapter 059. Bleeding and Thrombosis (Part 7) The most important point in a history related to venous thrombosis iswhether the thrombotic event was idiopathic (meaning there was no clearprecipitating factor) or was a precipitated event. In patients without underlyingmalignancy, having an idiopathic event is the strongest predictor of recurrence ofvenous thromboembolism. In patients who have a vague history of thrombosis, ahistory of being treated with warfarin suggests a past DVT. Age is an importantrisk factor for venous thrombosis; the risk of DVT increases per decade, with anapproximate incidence of 1/100,000 per year in early childhood to 1/200 per yearamong octogenarians. Family history is helpful in determining if there is a geneticpredisposition and how strong that predisposition appears to be. A genetic thrombophilia that confers a relatively small increased risk, suchas being a heterozygote for the prothrombin G20210A or factor V Leidenmutation, may be a relatively minor determinant of risk in an elderly individualundergoing a high risk surgical procedure. As shown in Fig. 59-5, a thromboticevent often has more than one contributing factor. Predisposing factors must becarefully assessed to determine the risk of recurrent thrombosis, and withconsideration of the patients bleeding risk, determine the length ofanticoagulation. Similar consideration should be given to determining the need totest the patient and family members for genetic thrombophilias. Figure 59-5 Thrombotic risk over time. Shown schematically is an individuals thrombotic risk over time. Anunderlying Factor V Leiden mutation provides a theoretically constant increasedrisk. The thrombotic risk increases with age and, intermittently, with oralcontraceptive (OCP) or hormone replacement (HRT) use; other events mayincrease the risk further. At some point the cumulative risk may increase to thethreshold for thrombosis and result in deep venous thrombosis (DVT). Note: Themagnitude and duration of risk portrayed in the figure is meant for example onlyand may not precisely reflect the relative risk determined by clinical study. [FromBA Konkle, A Schafer, in DP Zipes et al (eds): Braunwalds Heart Disease, 7th ed.Philadelphia, Saunders, 2005; modified with permission from FR Rosendaal:Venous thrombosis: A multicausal disease. Lancet 353:1167, 1999.] Laboratory Evaluation Careful history taking and clinical examination are essential components inthe assessment of bleeding and thrombotic risk. The use of laboratory tests ofcoagulation complement, but cannot substitute for, clinical assessment. No testprovides a global assessment of hemostasis. The bleeding time has been used toassess bleeding risk; however, it does not predict bleeding risk with surgery and isnot recommended for this indication. The PFA-100, an instrument that measuresplatelet-dependent coagulation under flow conditions, is more sensitive andspecific for platelet disorders and vWD than the bleeding time; however, it is notsensitive enough to rule out underlying mild bleeding disorders. Also, it has notbeen evaluated prospectively to determine its utility in predicting bleeding risk,although such studies are underway. For routine preoperative and preprocedure testing, an abnormalprothrombin time (PT) may detect liver disease or vitamin K deficiency that hadnot been previously appreciated. Studies have not confirmed the usefulness of anactivated partial thromboplastin time (aPTT) in preoperative evaluations inpatients with a negative bleeding history. The primary use of coagulation testingshould be to confirm the presence and type of bleeding disorder in a patient with asuspicious clinical history. Because of the nature of coagulation assays, proper sample acquisition andhandling is critical to obtaining valid results. In patients with abnormalcoagulation assays who have no bleeding history, repeat studies with attention tothese factors frequently results in normal values. Most coagulation assays areperformed in sodium citrate anticoagulated plasma that is recalcified for the assay.Because the anticoagulant is in liquid solution and needs to be added to blood inproportion to the plasma volume, incorrectly filled or inadequately mixed bloodcollection tubes will give erroneous results. Vacutainer tubes should be filled to>90% of the recommended fill, which is usually denoted by a line on the tube. Anelevated hematocrit (>55%) can result in a false value due to a decreased plasmato anticoagulant ratio.