**Venous Thromboembolism in Bariatric Surgery**

Eleni Zachari, Eleni Sioka, George Tzovaras and Dimitris Zacharoulis  *Department of Surgery, University Hospital of Larissa Greece* 

#### **1. Introduction**

66 Pulmonary Embolism

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ISSN (printed): 0002-0729

212-7, ISSN 0006-9248

Deep venous thrombosis (DVT) and pulmonary embolism (PE) constitute clinical presentations of the same vascular disease, known as venous thromboembolism (VTE). VTE is responsible for hospitalization of >250000 Americans annually. It is associated with high morbidity and mortality and represents a primary cause of preventable death. There is strong evidence that obesity is an independent risk factor for DVT and PE. Bariatric surgery is proven to be an effective means in the therapy of morbid obesity and its related comorbidities, thus its prevalence is rapidly increasing. Well established and widely performed procedures include laparoscopic adjustable gastric band (LAGB), Roux-en-Y gastric bypass (RYGBP), biliopancreatic diversion (BPD, with or without duodenal switch) and sleeve gastrectomy (SG). LAGB is a purely restrictive method, while RYGBP and BPD are considered as mainly malabsorbptive procedures. SG was performed as a bridge to further by-pass surgery, however nowadays is performed as a single stage procedure. The risk of VTE in patients undergoing elective bariatric surgery is high, attributable to obesity, intraoperating factors and the lack of an established guidance describing optimal VTE prophylaxis. Overall incidence of VTE in this population is reported to be 1-3%. Diagnosis of PE postoperatively in obese patients can be difficult due to physical limitations and consequently may be underdiagnosed. Furthermore, although VTE is usually diagnosed as immediate postoperative complication, PE can occur in nonhospitalized patients, within the first month after surgery, despite pharmacologic prophylaxis.

#### **2. Obesity**

The most widely applied tool to diagnose obesity is body mass index (BMI). BMI is defined as weight in kilograms divided by the square of height in meters. World health Organization defines obesity as a BMI≥ 30. This cutoff was selected because according to epidemiological studies mortality curve increases at this value. Moreover, morbid obesity is defined as BMI≥40.

The prevalence of obesity increases rapidly in both developed and developing countries and is considered as one of the most serious public health problems.

Recent scientific data from long-term studies support the strong association between obesity and type 2 diabetes, hypertension, cardiovascural disease, dyslipidemia, arthritis, gallbladder disease, sleep apnea syndrome and many types of cancer. Furthermore, obesity deteriorates quality of life and induces severe psychological disorders.

Venous Thromboembolism in Bariatric Surgery 69

Morbid (BMI>50) and truncal obesity are identified as major predisposing factors for VTE. Sedentary lifestyle, increased abdominal pressure and excessive weight resting on the inferior vena cava drainage attribute to the increased risk. Additional risk factors include advanced age, history of previous VTE, immobilization, venous insufficiency and stasis, smoking, estrogen- containing oral contraceptives and hormone replacement therapy, hypercoaguable state, hypoventilation syndrome and anastomotic leakage. According to current literature, obesity interferes in intrinsic and extrinsic coagulation pathways, as well as in the anticoagulant mechanism, leading to a hypercoagulating state. Plasma concentration of fibrogen, von Willebrand, t-PA, PAI-1 and factor VII are significantly elevated in obese patients, while platelet aggregation is promoted due to leptin. There is evidence that treatment of morbid obesity can reverse partially some of the above abnormalities, as weight loss is associated with significant reduction in fibrogen, t-PA, PAI-1

Perioperative factors contributing to VTE include extend of surgical trauma, operative duration, length of postoperative immobilization and the use of general versus regional anesthesia. The risk of developing VTE depends on the type of major abdominal surgical procedure. Mukherjee et al. reported lower incidence of VTE among bariatric surgery patients (0.35%), while VTE rates were higher in patients undergoing nephrectomy, hepatectomy, colorectal resection, splenectomy, gastrectomy, pancreatectomy and esophagectomy. This lower rate may reflect strict adherence of bariatric surgeons to VTE

More specifically, in laparoscopic bariatric surgery, reverse Trendelenburg position and pneumoperitoneum are associated with venous stasis of lower extremity and impaired venous return due to the compression of iliac veins and inferior vena cava. Furthermore several studies show the development of a hypercoagulable state during laparoscopy. Conversely, the risk of VTE during laparoscopy could be compensated by lower degree of surgical injury, early mobilization and reduced postoperative acute-phase response. Podnos et al. in a review of 3464 cases of GBP demonstrated that although the difference was not statistically significant, the incidence of PE was lower in laparoscopic group rather than the open group. In absence of randomized controlled studies, the evidence remains inconclusive

Mechanical modalities include graduated compression stockings, intermittent pneumatic compression devices (IPC) and venous foot pump. Perioperative use of the above devices and early mobilization of patients reduce the risk of VTE by increasing venous outflow and preventing venous stasis. Remarkable advantage of mechanical prophylaxis is lack of interference in the coagulation path, which renders it safe for patients in high risk for bleeding.

Unfractionated heparin (UFH) and low molecular weight heparins (LMWH) are effective in the prophylaxis of VTE in surgical patients. An initial dose of 5000 units UFH is

Limitations of the use of mechanical devices are skin irritation and poor compliance.

**4.1 Predisposing factors to venous thromboembolism in bariatric surgery** 

**4. Venous thromboembolism** 

and improvement of deficiency of antithrombin III.

prophylaxis guidelines relative to other surgical specialties.

as to the relative risk of VTE after laparoscopic bariatric surgery.

**4.2.1 Mechanical prophylaxis** 

**4.2.2 Pharmacological prophylaxis** 

**4.2 Prophylaxis of venous thromboembolism in bariatric surgery** 
