Moderate/High VTE Risk
Key Points:
- Pharmacologic prophylactic regimens are started one to two hours prior to surgery.
- Aspirin is not recommended as an anticoagulation regimen.
- For short-term prophylactic anticoagulation there are relatively few conditions with excessive bleeding risk or other considerations that would contraindicate anticoagulation.
Moderate-risk patients include:
- Major surgery in those less than 40 years of age
- Minor surgery in those age 40 to 60
- Minor surgery in those less than age 40 with additional risk factors (prior VTE, cancer, hypercoagulability)
Without prophylaxis, moderate-risk VTE patients have a 2 to 4% proximal DVT risk, 1 to 2% clinical PE risk, and a 0.1 to 0.4% risk of fatal PE.
High-risk patients include:
- Minor surgery in those over 60 years of age without additional risk factors
- Major surgery in those over 40 years of age without additional risk factors
- Minor surgery in those over 40 years of age with additional risk factors (prior VTE, cancer, hypercoagulability)
Without prophylaxis, high-risk VTE patients have a 4 to 8% proximal DVT risk, 2 to 4% clinical PE risk, and a 0.4 to 1.0% risk of fatal PE.
See Annotation #2, "Assess VTE Risk for Procedure-Related and/or Patient-Related Risk Factors" (for patient-related risk factors see the original guideline document).
Evidence supporting this recommendation is of classes: B, D, R
VTE Prophylaxis Plan for Moderate/High VTE Risk
In addition to patient education and early ambulation, all patients with moderate risk for VTE should receive elastic graded compression stockings, intermittent pneumatic compression if immobilized, and pharmaco-logic prophylaxis unless contraindicated. Pharmacologic regimens reduce compliance issues and have been shown to reduce the incidence of postoperative VTE.
Selecting a Pharmacologic Agent
Three issues that need to be addressed are choice of agent, dosing, and duration of therapy. For moderate-risk patients who do not have a contraindication to pharmacologic prophylaxis, the current choice is between LMWH and UFH started 1 to 2 hours prior to surgery, subcutaneously every 8 to 12 hours. Aspirin has not been shown to be an effective agent in general surgical patients and is not recommended.
UFH is cost effective and effective in reducing the risk of postoperative VTE in moderate-risk patients. While LMWH has the convenience of single-day dosing, it is not superior to UFH and is significantly more expensive. Further, overall complication rates appear similar between UFH and LMWH.
Studies, primarily in patients over 40 years of age, have shown that UFH is as effective as LMWH as an anticoagulant prophylactic agent for moderate- and high-risk surgical patients. [Conclusion Grade I: See Conclusion Grading Worksheet A - Annotation #7, 8 (Selecting Heparin) in the original guideline document]
See Appendix C, "Pharmacologic Prophylaxis Table" for more information.
- Mechanical Prophylaxis
Data suggest that below knee and above knee stockings are equally effective and the effectiveness of stockings is enhanced when combined with other measures. Side effects are rare, although a proper fit, particularly in the obese, may be difficult in 10-15% of patients. In general, the data would not support the use of elastic stockings as the sole measure in this group.
The clinical implications of this are unknown although augmentation with foot pumps was less than with IPC devices. Foot pumps may be better tolerated and can be applied in cases in which the leg is not available for placement of an IPC device but the work group is not aware of any studies comparing IPC and foot pumps in general surgery or trauma patients.
See Annotation #4 for more information on elastic graded compression stockings and intermittent pneumatic compression devices.
Although the work group recommends all of the above non-pharmacologic methods for high-VTE-risk patients, the work group also strongly recommends pharmacologic prophylaxis in these patients unless specifically contraindicated. There is no substitute for critical assessment and judgment on the part of the clinician when considering the relative benefits and risks of prophylactic anticoagulation.
Evidence supporting this recommendation is of classes: A, C, M, R
Supportive Statements for Pharmacotherapy of High-VTE-Risk Patients:
- For most general surgery patients, UFH remains the agent of choice. LMWH has been found to be as safe and effective yet remains significantly more expensive.
- In general surgery, patients may receive preoperative heparin without increased risk of bleeding.
- LMWHs cause less heparin-induced thrombocytopenia (HIT) than UFH. There is early evidence to support the use of fondaparinux in HIT although further confirmatory studies are needed.
- LMWH should be adjusted at prophylactic doses for patients with a creatinine clearance less than 30 mL/minute. The manufacturer-recommended dose of enoxaparin is 30 mg daily in this population; the manufacturer of dalteparin does not list a similar dose recommendation.
- Fixed-dose prophylaxis in the severely obese patient will likely result in underdosing. Current expert opinion suggests that LMWH be increased by 25% in the very obese patient (body mass index [BMI] 35 or more): for example, enoxaparin 40 mg every 12 hours.
- In gynecologic surgery, evidence is strongest to support use of UFH. For patients with malignancy, a regimen of every-8-hour dosing should be maintained.
Additional patient related risk factors may place younger patients and/or those with more minor procedures into the high-risk category. (See Annotation #2 in the original guideline document for more information.)