Thromboembolic disease: The case for routine prophylaxis
Preventive strategies can reduce fatal pulmonary embolism as much as 75% in gynecologic surgery patients. This article explains the evidence on how to assess risk and choose mechanical and drug therapies for these women, including gravidas.
TABLE 4
Incidence of thromboembolic events based on level of risk
| SITE OF THROMBOSIS | RISK LEVEL (%) | |||
|---|---|---|---|---|
| Low | Moderate | High | Very high | |
| Calf veins (distal) | 2 | 10–35 | 30–60 | 63.5 |
| Iliofemoral veins (proximal) | 0.4 | 2–8 | 5–10 | 10–20 |
| Pulmonary emboli | 0.2 | 1–2 | 2–4 | 4–10 |
| Fatal pulmonary emboli | 0.002 | 0.1–0.5 | 0.4–1 | 0.2–5 |
| Source: Modified from Geerts WH, et al.13 | ||||
Drug and mechanical therapies
Strategies for preventing thromboembolic disease attempt to mitigate the impact of venous stasis, endothelial injury, and hypercoagulable states. Traditionally, early ambulation, adequate hydration, and elevation of the lower extremities have been used, because they are simple and inexpensive interventions.
More recently, pharmacologic and mechanical therapies have proven effective in reducing the incidence of DVT and fatal pulmonary emboli. Prophylactic measures commonly used today are:
- graduated compression stockings
- external pneumatic leg or foot compression devices
- low-dose unfractionated heparin
- low molecular weight heparin
MECHANICAL THERAPIESGraduated compression stockings
Compression stockings are one of the earliest methods of preventing perioperative thrombosis. Compression is greatest at the toe and gradually diminishes toward the thigh. When Belcaro14 studied the risk of recurrent venous thrombosis in nonsurgical hospitalized patients, thrombosis recurred in 40% of patients with no therapy, but only 9.4% of patients wearing graduated compression stockings (GCS). Adding oral antiplatelet therapy lowered the risk to 2%. However, GCS were not superior to any other method of preventing recurrent DVT.
As for surgical patients, a single study15 demonstrated protection against DVT when compared with no GCS in elective gynecologic surgery patients.
Today, GCS are usually a perioperative adjunct to other preventive methods, to provide added protection.
Proper fitting by trained personnel is vital; otherwise, a tourniquet effect may cause venous stasis and reduce benefit.
Sequential pneumatic compression devices
Like GCS, these devices decrease the caliber of veins by simple compression. They also increase blood flow velocity and stimulate the endogenous fibrinolytic system.
Enhanced fibrinolytic activity due to intermittent compression occurs even if the device is used on only 1 lower extremity, or on an upper extremity. Patient and nursing-staff compliance may affect efficacy. Sequential pneumatic compression devices (SPCDs) may be thought inconvenient, impeding nursing functions. Some patients may find the repetitive inflation-deflation cycles annoying.
These devices must be activated prior to surgery and continued for a minimum of 24 hours. Some studies suggest that SPCDs be used for 5 days in high-risk situations.16
Calf- and thigh-length devices have similar effects. Rare complications include peroneal nerve injury and compartment syndrome.
What the data show. In an analysis of 4 trials comparing SPCDs with no therapy, thromboembolic disease occurred in only 2% of patients who wore SPCDs but in 20% of those who did not.17 Compared with low-dose unfractionated heparin, no difference in the rate of DVT was seen.18 However, risk of transfusion and retroperitoneal drainage volume increased in the heparin group.
Contraindications include active or suspected DVT, congestive heart failure, known pulmonary embolus, and leg injuries.19
Combined therapy may be best for high-risk women. A study20 of women who developed thromboemboli despite appropriate treatment with SPCDs found the women more likely to be older than 60 years and/or to have cancer or history of thromboembolic disease or hypertension. This high-risk group may benefit from combined therapy.
Foot compression devices resemble booties and mimic the plantar compression that occurs during walking. They increase blood-flow velocity, stimulate the endogenous fibrinolytic system, and have the same indications as SPCDs. However, they are only moderately effective in reducing venous thrombosis.21 Potential drawbacks are that the devices must be removed when the patient ambulates and replaced when she returns to bed.
DRUG THERAPIESLow-dose unfractionated heparin
Heparin alters the molecular configuration of antithrombin III, making it 1,000 to 4,000 times more potent as an inhibitor of thrombin formation, which in turn limits conversion of fibrinogen to fibrin. This prolongs the activated partial thromboplastin time (aPTT) commonly used to monitor patients receiving full anticoagulation therapy.
A naturally occurring mucopolysaccharide with a molecular weight ranging from 3,000 to 30,000 daltons, heparin is richly concentrated in mast cells. Its anticoagulant properties relate primarily to interaction with antithrombin III (also known as heparin cofactor II), factor IXa, factor Xa, factor XIa, factor XIIa, and platelet aggregation.22
Heparin also inhibits the effects of factor Xa on the coagulation cascade and limits platelet aggregation.23
Half-life is 1 hour for intravenous heparin and about 3 hours for subcutaneous heparin.
Use in pregnancy. Low-dose unfractionated heparin (LDUH) does not cross the placenta and is safe to use during pregnancy.
What the data show. Randomized clinical trials conducted prior to 1988 showed venous thrombosis decreased by 70% and pulmonary embolus by 50% in patients treated with LDUH, compared with those receiving no therapy.24
Dosing options. LDUH typically is given as a 5,000-U dose 2 hours before surgery. The single preoperative dose seems to be as effective as multiple preoperative doses.25 Postoperative therapy is instituted 8 to 12 hours after surgery; heparin is given every 8 to 12 hours until the patient is fully ambulatory.
