Epidemiology

Each year, surgeons in the United States perform more than 46 million inpatient surgeries, the majority of which are nonorthopedic surgeries. Patients undergoing nonorthopedic surgeries are a heterogeneous group in terms of surgery type, comorbidities, and associated risk for venous thromboembolism (VTE), which comprises deep vein thrombosis (DVT) and pulmonary embolism (PE). Patients at low risk for VTE typically undergo surgical procedures lasting less than 30 minutes, are immediately mobile following surgery, or are already receiving therapeutic-dose anticoagulant therapy. All other surgical patients are considered to be at moderate or higher risk for VTE and merit some form of prophylaxis. VTE in the patient undergoing nonorthopedic surgery can cause significant morbidity and mortality and is a common cause of readmission to the hospital.

Pathophysiology

Many factors contribute to VTE after nonorthopedic surgery (Table 58-1).

Trauma and surgery both contribute to venous injury and activation of the coagulation system. Postoperatively, patients may have persistently reduced mobility, which causes stasis of blood flow in the deep venous system. Patients undergoing certain types of surgery may also have independent risk factors for VTE, such as obesity in the bariatric surgical patient.

As in the orthopedic surgery setting, most episodes of postoperative DVT in nonorthopedic surgery are clinically silent. These unnoticed clots usually resolve spontaneously without administration of antithrombotic therapy. However, 25% to 50% grow and cause symptomatic DVT or PE.

Does This Patient Undergoing General Surgery Need VTE Prophylaxis?

Data from studies done more than 20 years ago involving patients who did not routinely receive thromboprophylaxis found that rates of asymptomatic DVT in patients having general surgical procedures were between 15% and 30%, while rates of fatal PE occurred in 0.2% to 0.9% of patients. Current surgical practices, including improved perioperative care, rapid postoperative mobilization, and greater use of regional anesthesia have likely reduced these figures. However, general surgery patients are still considered to be at moderately high risk of VTE. Numerous randomized clinical trials and meta-analyses have shown that thromboprophylaxis with low-dose unfractionated heparin (LDUH) and low-molecular-weight heparin (LMWH) reduce the risk of asymptomatic DVT and symptomatic VTE by more than 60% in these patients.

Patients with no additional risk factors, who have short (<30 minute) procedures, and who can mobilize postoperatively, do not require any specific thromboprophylaxis. All other patients should be evaluated for VTE prophylaxis. Patients at a low risk for bleeding should receive pharmacologic prophylaxis with low dose unfractionated heparin (LDUH), low molecular weight heparin (LMWH), or fondaparinux. There have been no trials that directly compare the two most popular dosing regimens of subcutaneous LDUH, 5000 units every 8 hours and 5000 units every 12 hours. There have been several trials comparing LMWH and LDUH, and both are considered equally efficacious. There is conflicting evidence regarding the safety of LMWH versus LDUH, but a recent meta-analysis showed that lower doses of LMWH were associated with less bleeding than LDUH. Our practice is to use the lowest recommended dose of heparin for prophylaxis, to minimize bleeding complications, and reduce the number of injections that a patient must receive. The selective factor Xa inhibitor fondaparinux has also been evaluated for major abdominal surgery. There does not appear to be any significant difference in VTE, major bleeding, or death when fondaparinux is compared with LMWH.

Mechanical thromboprophylaxis is an option in patients with a high risk of bleeding. However, graduated compression stockings (GCS) and intermittent pneumatic compression devices (IPC) are not as effective as pharmacologic prophylaxis, and do not appear to reduce the risk of proximal DVT or symptomatic PE. Though many use them as an “add-on intervention” in general surgery patients who are at particularly high risk of VTE, such as those with cancer, there is little evidence that they add to the protective effect of pharmacologic prophylaxis.

The evidence for extended thromboprophylaxis in general surgery is not as robust as in orthopedic surgery. One trial showed that the incidence of asymptomatic DVT in cancer surgery patients was lower in patients who had their LMWH continued for two to three weeks after hospital discharge; however, this trial only included patients undergoing cancer surgery. At this time, it is not recommended that all general surgery patients receive extended thromboprophylaxis. However, cancer patients who are at particularly high risk of VTE should be considered for postdischarge prophylaxis for two to three weeks.

Does This Patient Undergoing Gynecologic or Urologic Surgery Need VTE Prophylaxis?