There are many inherited and acquired risk factors associated with VTE and recurrent VTE (Table 4.1). Strong genetic risk factors that lead to a hypercoagulable state include deficiencies in the anticoagulants antithrombin, protein C, and protein S. Moderate genetic risk factors include factor V Leiden, prothrombin G20210A, and non-type O blood (Table 4.2). Acquired risk factors include age, surgery, obesity, cancer, pregnancy, hormone-based contraceptives, hormone replacement, antiphospholipid syndrome, acute infection, immobilization, indwelling catheter use, paralysis, prolonged travel, smoking, hospitalization, reduced fibrinolysis, and acquired thrombophilia.

Plasma markers used to screen for inherited thrombophilia include factor V Leiden mutation, low protein C activity, low protein S activity, and free protein S deficiency. Markers for acquired thrombophilia include D-dimer elevation, fibrinogen elevation, elevation of coagulation factors VIII, IX, and XI, elevation of lupus anticoagulants and homocysteine level, and antithrombin III deficiency (Table 4.2). One study screened bariatric surgery candidates and found that serologic markers occurred more frequently than what would be expected in the general population. Results included D-dimer elevation in 31 %, fibrinogen elevation in 40 %, factor VIII elevation in 50 %, factor IX elevation in 64 %, factor XI elevation in 50 %, and lupus anticoagulant in 13 % [9]. One study identified clinical markers of a hypercoagulable state using rotational thromboelastometry (ROTEM) in patients being prepared for bariatric surgery. ROTEM detects hyperfunctional changes to determine if a hypercoagulable state exists by looking at clot starting time, clot formation time to 20 mm, maximum clot firmness, and clot lysis. Metabolic and inflammatory markers, such as leptin, C-reactive protein, fibrinogen levels, and platelet count, were noted to be significantly higher in the high-risk patients and it was concluded that a hypercoagulable state is associated with central obesity and high fibrinogen levels [10].

Patients undergoing elective general surgery, including bariatric surgery, are at relatively low risk of VTE. Specifically, the incidence of VTE is approximately 0.03 % with inguinal hernia repair and laparoscopic cholecystectomy, 0.1 to 0.6 % with operations involving the abdominal wall or appendix, and up 1.7 % with major resections such as esophagectomy, hepatectomy, and splenectomy. Most large series report VTE rates after bariatric surgery of about 0.4 % [6].

Most studies report the highest risk for VTE within the first 3–4 weeks and up to 3 months postoperatively. However, there are some studies suggesting that VTE risk remains elevated for at least 6 months in the postoperative period [37–40].

Using data from nearly 74,000 patients, the Bariatric Outcomes Longitudinal Database (BOLD) demonstrated a VTE incidence of 0.42 % at 90 days, with a risk of approximately 1.5 % after open surgery compared to 0.34 % laparoscopically [41]. The Longitudinal Assessment of Bariatric Surgery (LABS) study reported a 30-day VTE rate of 0.4 % [43].

Analyzing the VTE events in 93 of 27,818 patients (0.33 %), the Michigan Surgery Collaborative (MBSC) reported a DVT rate of 0.21 %, a PE rate of 0.18 %, and both a DVT and PE in 0.06 % [44]. In this dataset there were eight VTE-associated deaths, giving a case fatality rate of 8.6 % and accounting for one-third of all deaths in the registry.

In a large, multi-institutional retrospective chart review of 4293 patients undergoing primary or revisional bariatric surgery over an 8-year period, 57 patients (1.3 %) had a VTE [46]. Pulmonary embolism occurred in 39 (0.9 %), and DVT occurred 18 (0.4 %). Of note, no patients were denied surgery due to risk of VTE. Interestingly, of the patients with PE, 38.5 % had negative duplex studies of the lower extremities. There was only one VTE-related mortality in this study (0.02 %).

Gastric bypass was more likely to result in VTE events than LAGB (OR = 0.31). The incidence of VTE at 6 months for the different operations were as follows: LAGB 0.8 % (n = 616), laparoscopic RYGB 2.7 % (n = 5695), and open RYGB 3.3 % (n = 11,123).

Despite significant advances in the prevention and treatment of VTE, pulmonary embolism remains the most common preventable cause of hospital death, responsible for many deaths each year in the USA. Thus, it is vital that efforts continue to be made to find the safest and most effective means of preventing and managing VTE. Practical approaches to the prevention of VTE in surgical bariatric patients are reviewed here.

According to the Agency for Healthcare Research and Quality, the prevention of VTE is the number one strategy to improve patient safety in hospitals [51]. As an example, as part of the Surgical Care Improvement Project, the Center for Medicare and Medicaid Services (CMS) now considers appropriate VTE prophylaxis to be a pay-for-performance quality measure for specific procedures (see Table 4.3) [52–54]. Effective and safe prophylactic measures are now available for most high-risk patients [55–58] and numerous evidence-based guidelines have been published for the prevention of VTE [59–61]. The American College of Chest Physicians clinical practice guidelines recommend VTE prophylaxis by surgical risk groups [60].

In the absence of appropriate prophylaxis, the incidence of asymptomatic DVT detected by objective diagnostic screening tests has ranged from 10 to 80 % in various hospitalized medical and surgical groups. From earlier studies, the incidence of fatal pulmonary embolism in the absence of prophylaxis was estimated to be 0.1 to 0.8 % in patients undergoing elective general surgery, which includes bariatric surgery, 2 to 3 % in patients having elective total hip replacement, and 4 to 7 % of patients undergoing surgery for a fractured hip [59].

These estimates are likely lower today because of the increasing use of early ambulation and shorter lengths of hospitalization. However, the incidence of VTE, and in particular fatal pulmonary embolism, remains excessively high, even after hospital discharge.

Most bariatric surgery patients are considered at high risk for VTE given the prevalence of risk factors that promote VTE, including obesity, obstructive sleep apnea/hypoventilation syndrome, and exposure to general anesthesia.