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Perioperative anticoagulation:
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Earn Category I CME credit by reading this article and the associated article and successfully completing the post-test. Successful completion is defined as a cumulative score of at least 70% correct. This material has been reviewed and is approved for 1 hour of clinical Category I (Preapproved) CME credit by the AAPA. The term of approval is for 1 year from the publication date of June 2004. |
Learning objectives
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More than 1 million patients in the United States who have atrial fibrillation, a prosthetic heart valve, or a history of venous thromboembolism (VTE) use warfarin (Coumadin) therapy to prevent thrombus formation.1 Although the standard of care for chronic anticoagulation has been well established, the management of warfarin therapy in the perioperative setting is less well understood. Recent studies suggest that a sound approach to managing perioperative anticoagulation is to weigh the risk of thrombosis against the risk of bleeding.2
The term heparin window or heparin bridge describes the time before and after a surgical procedure when a patient's warfarin therapy is replaced with either unfractionated or low-molecular-weight heparin (LMWH). The standard protocol is to discontinue warfarin 4 or 5 days before the scheduled procedure, initiate unfractionated IV heparin or LMWH after the international normalized ratio (INR) falls below the therapeutic range, and then discontinue heparin before surgery (4-5 hours before surgery when using unfractionated IV heparin and 12-24 hours before surgery when using LMWH). After surgery, when the risk of bleeding is minimized, both heparin and warfarin are restarted. Once the INR is within the therapeutic range, heparin therapy is stopped, while oral anticoagulation using warfarin continues.3
Chronic warfarin therapy is used to prevent thromboembolic complications in patients who have atrial fibrillation, certain prosthetic heart valves, or a history of VTE. The decision to implement the heparin window rather than temporarily discontinue anticoagulation must be based on the patient's risk of an embolic event.
Atrial fibrillation Chronic atrial fibrillation is the most common reason for oral anticoagulation therapy. Recent studies have reported that the daily risk of stroke for patients with atrial fibrillation who are not using anticoagulation is 0.003% to 0.05%. The calculated yearly risk of 1% to 20%4 depends on other comorbidities, such as prior stroke, hypertension, valvular disease, increasing age, reduced left ventricular function, and diabetes (see Table 1).2
TABLE 1
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| Condition |
Daily risk of thromboembolism, %
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| Atrial fibrillation |
0.003-0.05
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| Mechanical prosthetic heart valve |
0.02-0.06
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| VTE <1 mo |
1
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| VTE <2-3 mo |
0.2
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| VTE >3 mo |
0.04
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| VTE = venous thromboembolism. | |
| Data from Spandorfer.4 | |
Prosthetic heart valves Currently, patients who have bioprosthetic porcine or bovine valves do not require chronic anticoagulation beyond the sixth month after valve replacement. Having a first-generation mechanical valve (Starr-Edwards ball valve, Björk-Shiley valve, or Lillehei-Kaster valve) is associated with a higher risk of thromboembolic events.5,6 Second-generation valves (St. Jude Medical valves and Medtronic-Hall valves) are associated with a lower risk of embolic events; note, however, that prosthetic mitral valves are associated with a slightly higher risk compared with aortic valves. Mechanical prosthetic valves confer a daily risk of 0.02% to 0.06% for a thromboembolic event, based on an annual risk of 8% to 22%.4
The use of vitamin K to reverse anticoagulation in an emergent situation in patients who have a mechanical valve has been associated with hypercoagulable states and an increased risk of thrombus, particularly postoperatively. The American College of Cardiology/American Heart Association guidelines recommend using fresh frozen plasma instead of vitamin K to achieve emergent preoperative reversal of anticoagulation in patients who have a prosthetic valve.7 Vitamin K should not be used to acutely reverse warfarin in patients with mechanical heart valves.7
Venous thromboembolism Chronic warfarin therapy also is used in the treatment of deep venous thrombosis and pulmonary embolism, together referred to as VTE. In the perioperative setting, the risk of recurrent VTE depends on when the previous VTE occurred; the daily risk of a subsequent VTE occurring within 30 days of a first VTE is 1% if anticoagulation is withheld (overall risk of 40% within the first month).2 The daily risk decreases to 0.2% in the second and third months after the initial event and to 0.04% by the fourth month.4
Another factor to consider in the perioperative care of patients using oral anticoagulation is the theoretical risk of developing a hypercoagulable state after surgery. Although no clinical evidence has emerged showing that this happens, the theoretical risk has been well documented.8 Thus, the overall risk of VTE recurrence cannot be calculated.
Other conditions such as severe left ventricular dysfunction, hypercoagulable states, and apical thrombi also require chronic anticoagulation. Unfortunately, the daily risk of VTE among patients with these conditions is unknown.
Along with the risk of VTE, the risk of postoperative bleeding must be taken into account when managing perioperative anticoagulation. Although the risk of bleeding in patients using anticoagulation therapy is uncertain, the use of postoperative heparin is estimated to increase the absolute risk of bleeding by 3%.2 The risk of postoperative bleeding is multifactorial, depending on the surgical site, surgeon, and type of surgery. For example, ophthalmologic surgery, dental cleanings, and superficial dermatologic procedures are associated with lower risks of bleeding compared to intra-abdominal and urologic surgery (see Table 2).9 Most neurosurgeons recommend achieving a normal INR before surgery because of the high risk of bleeding associated with neurosurgical procedures. When considering whether to anticoagulate a patient with heparin after surgery, the type of procedure, surgical site, and bleeding risk must be taken into account.
TABLE 2
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| Low-risk procedures | High-risk procedures |
| Dental procedures (simple tooth extractions, restorations,
endodontics, prosthetics) Endoscopic procedures Ophthalmic surgery Superficial dermatologic procedures |
Epidural blockade anesthesia Major intra-abdominal surgery Radical prostatectomy |
| Data from Jacobs and Nusbaum9 and Spandorfer.4 | |
The decision to stop warfarin therapy temporarily because of a surgical procedure is based on the risk of thrombosis compared to the risk of postoperative bleeding. The surgeon should be consulted to determine the type of surgery planned, the typical bleeding associated with the procedure, and the required INR before surgery can be performed. Most surgeons prefer an INR of less than 1.5; others may want a completely normalized INR.
The risk of perioperative VTE is largely determined by the reason for using warfarin therapy (see Table 3). The 2001 American College of Chest Physicians guidelines on managing oral anticoagulation during invasive procedures suggest that patients who have a low risk of VTE do not require a perioperative heparin window.3 These patients can discontinue warfarin therapy 4 days before surgery to allow the INR to return to normal, and the INR is checked on the day of surgery to confirm that it is within the desired range. After surgery, warfarin therapy is resumed and the patient's INR is allowed to drift up to the therapeutic range.3
TABLE 3
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| Low risk of bleeding | High risk of bleeding |
| LOW RISK OF THROMBOSIS | |
| No heparin window required Consider continuing therapeutic oral anticoagulation |
No heparin window required Discontinue oral anticoagulation |
| HIGH RISK OF THROMBOSIS | |
| Heparin window required | Consider using modified heparin window |
| Data from Ansell et al,3 Jacobs and Nusbaum,9 and Spandorfer.4 | |
A patient who has a high risk of VTE requires perioperative use of heparin (see "The heparin window"), coordinated by the medical and surgical teams. A patient undergoing a procedure that is associated with a high risk of both bleeding and thrombosis if anticoagulation is withheld poses a difficult decision. When the surgery is not absolutely necessary, the risk of thrombosis outweighs the need for surgery (see Table 3). For example, a patient who develops deep venous thrombosis 2 weeks before a scheduled elective lumbar laminectomy has a high risk of subsequent thrombosis for several months after the initial event, but perioperative anticoagulation poses too great a bleeding risk for this neurosurgical procedure. This patient's elective laminectomy should be postponed until warfarin therapy is completed.
A modified heparin window may be used when surgery is urgent or emergent and the risk of both thrombosis and bleeding is high. This modified heparin window involves no administration of an initial heparin IV bolus, a longer postoperative heparin-free period, and lower-dose maintenance heparin infusion (with a partial thromboplastin time goal of 50-60 sec). These decisions are made on an individual basis, with close collaboration between the surgeon, primary care provider, and patient.
Dental procedures Patients need not interrupt their warfarin therapy before undergoing most dental procedures, provided the INR is within the therapeutic range.10 A meta-analysis of studies involving 774 patients undergoing various dental procedures showed that 98% of those receiving continuous anticoagulation had no serious bleeding problems after dental surgery (extractions, alveolar surgery, and gingival surgery).10 The 2% (n = 12) who had bleeding required systemic control, but none was seriously compromised. In patients who discontinued anticoagulation, 4 of 500 died of embolic complications, and 1 had two nonfatal complications.11 No difference in blood loss during oral surgery has been shown in patients who continued anticoagulation compared to those who stopped.10,12-14 The current recommendation in the dental literature is to maintain a therapeutic INR during dental surgery and control bleeding using local measures like tranexamic acid or epsilon amino caproic acid mouthwash.13
Endoscopic procedures Chronic anticoagulation may need to be discontinued temporarily for some endoscopic procedures. The American College of Gastroenterology recommends that when the endoscopic procedure is associated with a low risk of bleeding (for example, diagnostic esophagogastroduodenoscopy, flexible sigmoidoscopy and colonoscopy with or without biopsy, diagnostic endoscopic retrograde cholangiopancreatography, endosonography, and push enteroscopy), warfarin therapy may continue if the INR is within the therapeutic range.15 Patients undergoing endoscopic procedures that are associated with a high risk of bleeding (colonoscopic or gastric polypectomy, laser ablation coagulation, and endoscopic sphincterotomy) should have an INR of less than 1.5 before the procedure.15
Patients who have a low risk of developing VTE can discontinue warfarin therapy up to 5 days before the procedure and restart it after the procedure is completed.15 A heparin window may be needed in patients who have a high risk of VTE and who are undergoing an endoscopic procedure with a high risk of bleeding. Generally, elective endoscopic procedures in patients using temporary warfarin therapy should be postponed until after warfarin is discontinued.
Hypercoagulable states Patients who have a known hypercoagulable state and who have had a previous VTE are considered at high risk for further thrombotic events.3,8 These patients require a heparin window if oral anticoagulation is to be temporarily discontinued.
Two recent studies showed that LMWH and unfractionated heparin were equally beneficial for perioperative anticoagulation in patients who had mechanical valves. No VTEs were observed in one study of 60 patients with mechanical valves undergoing surgical procedures who received LMWH perioperatively.16 A daily savings of $390 was noted for patients who received LMWH as outpatients compared to those who received unfractionated heparin therapy in the hospital.16 Similar results were observed in a larger study (515 patients) using enoxaparin (Lovenox) and dalteparin (Fragmin).17 However, several cases have been reported recently of massive valve thrombosis in pregnant women with mechanical valves after they received enoxaparin for prophylactic therapy perioperatively.18 LMWH should be used with caution in pregnant patients or in patients with mechanical heart valves.
PAs practicing in primary care or a surgical subspecialty are frequently challenged when preparing patients on chronic warfarin therapy for surgery. In all cases, close collaboration with the surgeon is imperative to determine the best course of action. The clinician should categorize each patient as having a low or high risk of thrombosis, taking into account the guidelines for perioperative management of chronic anticoagulation. Does the benefit of surgery outweigh the risk of possible embolic events or bleeding complications? That is the question that should be asked each time this scenario is encountered, and for each patient, individual needs must be considered.
1. Spandorfer JM, Lynch S, Weitz HH, et al. Use of enoxaparin for the chronically anticoagulated patient before and after procedures. Am J Cardiol. 1999;84:478-480,A10.
2. Kearon C, Hirsh J. Management of anticoagulation before and after elective surgery. N Engl J Med. 1997;336:1506-1511.
3. Ansell J, Hirsh J, Dalen J, et al. Managing oral anticoagulant therapy. Chest. 2001;119(suppl 1):22S-38S.
4. Spandorfer JM. The management of anticoagulation before and after procedures. Med Clin North Am. 2001;85:1109-1116.
5. Tinker JH, Tarhan S. Discontinuing anticoagulant therapy in surgical patients with cardiac valve prostheses: observations in 180 operations. JAMA. 1978;239:738-739.
6. Martin R. Perioperative approach to the anticoagulated patient. Anesthesiol Clin North Am. 1999;17:813-830.
7. American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients with Valvular Heart Disease). ACC/AHA guidelines for the management of patients with valvular heart disease. J Am Coll Cardiol. 1998;32:1486-1588.
8. Kapural L, Sprung J. Perioperative anticoagulaion and thrombolysis. Perioperative anticoagulants and thrombolysis in congenital and acquired coagulopathies. Anesthesiol Clin North Am. 1999;17:923-958.
9. Jacobs LG, Nusbaum N. Thromboembolic disease and anticoagulation in the elderly: perioperative management and reversal of antithrombotic therapy. Clin Geriatr Med. 2001;17:189-202.
10. Wahl MJ. Dental surgery in anticoagulated patients. Arch Intern Med. 1998;158:1610-1616.
11. Wahl MJ. Myths of dental surgery in patients receiving anticoagulant therapy. J Am Dent Assoc. 2000;131:77-81.
12. Campbell JH, Alvarado F, Murray RA. Anticoagulation and minor oral surgery: should the anticoagulation regimen be altered? J Oral Maxillofac Surg. 2000;58:131-135.
13. Mehra P, Cottrell DA, Bestgen SC, Booth DF. Management of heparin therapy in the high-risk, chronically anticoagulated, oral surgery patient: a review and a proposed nomogram. J Oral Maxillofac Surg. 2000;58:198-202.
14. Souto JC, Oliver A, Zuazu-Jausoro I, et al. Oral surgery in anticoagulated patients without reducing the dose of oral anticoagulant: a prospective randomized study. J Oral Maxillofac Surg. 1996;54:27-32.
15. Eisen ME, Baron TH, Dominitz JA, et al. Guideline on the management of anticoagulation and antiplatelet therapy for endoscopic procedures. Gastrointest Endosc. 2002;55:775-779.
16. Galla JM, Fuhs BE. Outpatient anticoagulation protocol for mechanical valve recipients undergoing non-cardiac surgery. J Am Coll Cardiol. 2000;35(1 suppl A):531A. Abstract 1114-1164.
17. Johnson J, Turpie AG. Temporary discontinuation of oral anticoagulants: role of low molecular weight heparin. Thromb Haemost. 2001,86:P2323.
18. Berndt N, Khan I, Gallo R. A complication in anticoagulation using low-molecular weight heparin in a patient with a mechanical valve prosthesis. A case report. J Heart Valve Dis. 2000;9:844-846.
Zachary Hartsell. Looking through the heparin window: Perioperative anticoagulation. JAAPA June 2004;17:21-25.
Copyright © 2004, Advanstar Medical Economics Healthcare Communications at Montvale, NJ 07645-1742. All rights reserved.
