Critically ill patients are assumed to be at high risk of VTE and do not require stratification.23 For high-risk patients, prophylaxis with LMWH, low-dose unfractionated heparin (LDUH), or fondaparinux is recommended for the duration of admission.23 For patients at high risk of both VTE and bleeding, mechanical prophylaxis with intermittent pneumatic compression (IPC) is recommended instead of LMWH, LDUH, or fondaparinux.23
Surgery, like trauma (see next page), increases the risk of VTE and has been well studied. Prophylaxis after orthopedic surgery differs from that of other types of surgery.
In orthopedic surgery, risk depends on the procedure. For major orthopedic surgery, including total hip or knee arthroplasty and hip fracture surgery, VTE prophylaxis is recommended for 35 days postsurgically.43 LMWH is the preferred agent, although many other means have been shown to be beneficial.44 A recent systematic review demonstrated that aspirin is not inferior to other medications after hip or knee arthroplasty.45 No mechanical or pharmacotherapeutic prophylaxis is generally recommended after nonmajor orthopedic surgery.43
Nonorthopedic surgery is stratified by risk factors, using Caprini44 (TABLE 539). For medium-risk patients (Caprini score, 3-4) LDUH, LMWH, or IPC is recommended; for high-risk patients (Caprini score, ≥ 5) preventive treatment should combine pharmacotherapeutic and mechanical prophylaxis.46 A recent meta-analysis, comprising 14,776 patients, showed that surgical patients with a Caprini score ≥ 7 had a reduced incidence of VTE when given chemoprophylaxis, whereas patients whose score is < 7 do not benefit from chemoprophylaxis.43 When bleeding risk is high, IPC is recommended as sole therapy.43 Prophylaxis is not recommended when risk (determined by the Caprini score) is low.46
Post-hospitalization. Risk of VTE can persist for as long as 90 days after hospitalization; this finding has led to evaluation of the benefit of prolonged chemoprophylaxis.23 Extended-duration LMWH prophylaxis decreases the incidence of VTE, but at the cost of increased risk of major bleeding.47 Based on this evidence, guidelines recommend against prolonged-duration anticoagulation.23 A 2016 trial showed that 35 days of the direct-acting anticoagulant betrixaban reduced the risk of symptomatic VTE events, compared to 10 days of LMWH (NNT = 167), without increased risk of bleeding.48 This is a limited benefit, however, that is unlikely to change guideline recommendations.
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