© Springer International Publishing Switzerland 2017Andrew Loveitt, Margaret M. Martin and Marc A. Neff (eds.)Passing the Certified Bariatric Nurses Exam10.1007/978-3-319-41703-5_26
26. Complications of Bariatric Surgery: Venous Thromboembolism
Department of General Surgery, Rowan University, Stratford, NJ, USA
One of the major complications of bariatric surgery is venous thromboembolic (VTE) disease which manifests itself as deep venous thrombosis (DVT) and/or pulmonary embolism (PE). The risk of DVT is between 1 and 3 %, and PE is between 0.2 and 2 % within 30 days of bariatric surgery [1, 2]. While uncommon, PE is one of the leading causes of death within the postoperative period. There are multiple factors that place obese patients at higher risk for VTE :
Increased body weight by itself is an independent risk for VTE events. It leads to an increased intra-abdominal pressure and decreases venous return to the heart contributing to venous stasis.
Inactivity causes venous stasis and increased blood viscosity in the lower extremity veins that contributes to the formation of blood clot in the lower extremities.
Finally, there are also multiple obesity-related biochemical changes that contribute to the increased risk of VTE.
Bariatric surgery further contributes to the already increased risk of VTE events for obese patients :
Reverse trendelenburg positioning (head of the table up) and pneumoperitoneum (filling the abdomen with CO2) during surgery decrease venous return to the heart and thus contribute to a prothrombic state.
Decreased mobility after surgery secondary to pain.
Bariatric surgery patients are considered moderate to high risks of VTE events. Therefore, bariatric centers have implemented multiple VTE protocols. The guidelines for prevention of perioperative VTE events are variable. There are multiple accepted forms for DVT prevention such as mechanical compression devices, early ambulation, chemoprophylaxis, and sometimes the use of inferior vena cava filters (IVC). The majority of the bariatric surgeons routinely use (1) early ambulation, (2) pharmacologic agents, and (3) mechanical compression devices to prevent VTE complications. The most commonly used chemical agents are unfractionated heparin or enoxaparin [4, 5].
Heparin works by binding to the enzyme inhibitor antithrombin III (ATIII). It activates thrombin (factor IIa) and factor Xa. Heparin is reversible and has a short half-life. Prophylactic dosing of 5000 units every 8–12 h is common. The most serious side effect is heparin-induced thrombocytopenia (HIT). HIT is an antibody-mediated attack on platelets and can lead to significant bleeding as the platelet level drops. It is treated by discontinuation of all heparin products and starting other means of chemoprophylaxis.
Lovenox (low molecular weight heparin) is another popular chemoprophylactic agent among bariatric surgeons. It acts mostly on factor Xa. It requires less frequent administration and significantly lower risk of HIT, but compared to heparin, it is more expensive and the half-life is longer. Additionally it is not as easily reversible.
Inferior vena cava filters (IVCFs) are mechanical devices that trap venous thromboembolism that originates in lower extremities and can go to the lungs. They are usually placed into high-risk patients who have known hypercoagulable state, prior history of VTE, or very high BMI.
The most common complaint of a patient with a suspected DVT is lower extremity pain . While physical exam of the lower extremities is limited in the morbidly obese, you should look for swelling of the lower extremity, tenderness over the calf area, discoloration of the skin, or a palpable cord On physical exam, you can find swelling of the lower extremity, tenderness over the calf area, discoloration of the skin, or palpable cord. The most common modality used to evaluate for DVT is ultrasound of lower extremities. Ultrasound is noninvasive and has greater than 95 % sensitivity and specificity for proximal DVT. Findings suggestive of DVT on ultrasound will be noncompressibility of the vein and abnormal flow within the vein.