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Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physician Evidence-Based Clinical Practice Guidelines Online Only ArticlesApproach to Outcome Measurement in the Prevention of Thrombosis in Surgical and Medical Patients: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines
Section snippets
Thromboprophylaxis Reduces Fatal PE in Medical and Surgical Patients
Although some studies have limitations of lack of concealment and blinding, evidence from meta-analyses of randomized controlled trials (RCTs) strongly suggests that prophylaxis with an anticoagulant or aspirin reduces symptomatic VTE and fatal PE in medical and surgical patients (Table 1). In patients undergoing orthopedic, general, or urological surgery, unfractionated heparin (UFH) reduces the risk of fatal PE by about two-thirds1; in patients undergoing hip or knee arthroplasty or hip
Evidence Is Stronger for Anticoagulants and Aspirin Than for Mechanical Prophylaxis
Mechanical methods of thromboprophylaxis include graduated compression stockings, intermittent pneumatic compression (IPC) devices, and the venous foot pump. Relative to anticoagulants and aspirin, these methods have the advantage of not increasing bleeding. Moreover, comparisons of these agents against no prophylaxis suggest that they are effective in reducing thrombosis.
Unfortunately, these studies and others comparing mechanical and pharmaceutical agents are relatively few and small in size.9
Comparisons of Alternative Antithrombotic Agents Present Challenges
All the RCTs comparing two different antithrombotic agents have used asymptomatic DVT by mandatory venography as the primary outcome measure or as a component thereof. In general, any improvement in efficacy with any one agent was accompanied by an increase in bleeding. These studies are difficult to interpret because they do not provide information on the trade-off between benefits and risks in patient-important events.
The use of asymptomatic DVT detected by venography as a surrogate for a
Estimating Symptomatic VTE
In AT9, we considered possible strategies for estimating the absolute difference in the frequency of VTE associated with alternative approaches to antithrombotic management. To estimate the absolute benefit of one antithrombotic regimen over another in reducing VTE requires an estimate of the control group event risk and the relative risk reduction associated with the alternative or experimental antithrombotic regimen. In this section, we review the strategies we considered and discuss their
The AT9 Approach to Estimating Symptomatic VTE
Under different circumstances, with different bodies of evidence, any of strategies 1 to 3 might generate the highest-quality evidence. In the presence of rigorous observational studies and in the absence of large RCTs that show significant differences in symptomatic events between competing antithrombotic agents, strategy 3 will yield the highest-quality evidence. When large RCTs show convincing differences in symptomatic events between agents, strategy 1 will yield the highest-quality
Trading Off Symptomatic VTE and Bleeding
Having established best estimates of VTE and bleeding, making recommendations requires deciding on whether net benefit is optimized by administering or withholding antithrombotic prophylaxis. The relevant nonfatal events in medical and surgical prophylaxis are pulmonary embolus, DVT, and GI and surgical site bleeding. AT9 panelists17 rated the disutility (aversiveness or importance) of these events and judged them to be of similar importance to patients (DVT slightly less important; PE, GI, and
Conclusion
None of the approaches we have suggested for estimating the effect of antithrombotic prophylaxis is without problems arising from the conduct of screening ultrasound and venography. Subsequent studies should rely on clinical surveillance to detect symptomatic events.
Acknowledgments
Author contributions: As Topic Editor, Dr Guyatt oversaw the development of this article, including any analysis and subsequent development of the information contained herein.
Dr Guyatt: served as a Topic Editor and was responsible for drafting the entire article, with the exception of the first part on evidence regarding the impact of antithrombotic prophylaxis on mortality, and for final editing and content.
Dr Eikelboom: served as a panelist and was responsible for drafting the first part of
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Funding/Support: The Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines received support from the National Heart, Lung, and Blood Institute [R13 HL104758] and Bayer Schering Pharma AG. Support in the form of educational grants was also provided by Bristol-Myers Squibb; Pfizer, Inc; Canyon Pharmaceuticals; and sanofi-aventis US.
Disclaimer: American College of Chest Physician guidelines are intended for general information only, are not medical advice, and do not replace professional medical care and physician advice, which always should be sought for any medical condition. The complete disclaimer for this guideline can be accessed at http://chestjournal.chestpubs.org/content/141/2_suppl/1S.
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