by Salvatore Docimo, Jr., DO, MS
Salvatore Docimo, Jr., DO, MS, is Clinical Instructor and Fellow, Department of Minimally Invasive and Bariatric Surgery, Penn State Hershey Medical Center, Hershey, Pennsylvania.
Bariatric Times. 2015;12(12):18–22.
Patients undergoing bariatric surgery are at an increased risk for venous thromboembolism. Despite this elevated risk, no standardized risk assessment tools for venous thromboembolism exist. A review of the literature was performed that evaluated the three prophylactic options a clinician has in their armamentarium to prevent venous thromboembolism: mechanical (sequential compression devices; chemical prophylaxis, such as unfractionated heparin and low-molecular weight heparin; and inferior vena cava filters. Despite multiple clinical studies, there is no consensus on a venous thromboembolism prevention algorithm. However, a recent position paper released by the American Society for Metabolic and Bariatric Surgery provided recommendations regarding venous thromboembolism prevention thay may be used by surgeons as a guideline to make the best clinical decision for their bariatric patients.
Patients undergoing bariatric surgery are at an increased risk for venous thromboembolism (VTE).[1–4] The incidence of symptomatic deep venous thrombosis (DVT) and pulmonary embolism (PE) in patients following bariatric surgery ranges from 0 to 5.4 percent[5,6] and 0 to 6.4 percent, respectively.[7–8] However, most large, prospective studies have demonstrated a VTE incidence of less than one percent for average risk bariatric patients,[9–11] with the majority occurring following discharge from the hospital within 30 days. Though the incidence of VTE following bariatric surgery is comparable to other elective surgical procedures, VTE remains a leading cause of mortality after bariatric surgery.[14–16]
Currently, no standardized risk assessment tools for VTE exist. However, an awareness of significant risk factors is required in order to not only prevent VTE, but also to expeditiously diagnose and treat VTE. Risk factors for VTE among bariatric patients include a prior VTE, a higher body mass index (BMI), age, gender, lack of mobility, pulmonary hypertension, venous stasis disorders, an increased operative time, and type of surgical approach.[9–12]
Prophylaxis against for VTE is comprises three options: mechanical (sequential compression devices [SCDs]); chemical prophylaxis, such as unfractionated heparin (UFH) and low-molecular weight heparin (LMWH); and inferior vena cava filters.
Mechanical prophylaxis. Mechanical prophylaxis is primarily composed of sequential compression devices and also ambulation. Previous studies have evaluated the benefit of mechanical prophylaxis in isolation over chemical prophylaxis in order to eliminate the risk of bleeding complications associated with LMWH or unfractionated heparin. A retrospective review of 957 consecutive patients was performed to evaluate the ability of mechanical prophylaxis to prevent VTE. Patients enrolled in the study who underwent laparoscopic Roux-en-Y gastric bypass (RYGB) received only calf-length SCDs before surgery and frequent ambulation postoperatively.17 A thirty-day DVT and PE rates of 0.31 percent and 0.10 percent, respectively were noted, along with a bleeding complication rate of 0.73 percent, less than previous bleeding complication rates with LMWH (4.8%).[17,18]
Chemical prophylaxis. One of the largest studies to date evaluating chemical prophylaxis was performed by the Michigan Bariatric Surgery Collaborative (MBSC), which evaluated 24,775 patients who underwent bariatric surgery between 2007 and 2012. The study evaluated three prophylaxis strategies: UFH preoperatively and postoperatively (UFH/UFH), UFH preoperatively and LMWH postoperatively (UFH/LMWH), and LMWH preoperatively and postoperatively (LMWH/LMWH).19 Ninety-eight percent of the patients also received mechanical prophylaxis with SCDs. The rate of VTE was found to be lower for LMWH/ LMWH (0.25%) and UFH/LMWH (0.29%) groups than the UFH/UFH group (0.68%). The authors concluded LMWH is more effective than UFH for prevention of VTE among bariatric patients.
Limitations of the study do exist. For instance, complications such as the bleeding incidents associated with each various treatment modality was not adequately captured and described. The MBSC registry also did not capture any events that occurred beyond 30 days following the procedure. This could have significantly limited the number of VTE incidents.
In a study by Jamal et al, a total of 4,293 patients undergoing bariatric surgery were assessed. Fifty-seven patients (1.3%) were found to have a VTE incident. Of the 57, 17 patients who were discharge on an extended prophylaxis for 2 to 4 weeks postoperatively were also found to have developed a VTE. However, it should be noted only one VTE-related mortality from this group with the extended VTE prophylaxis was documented. The patients in the study underwent two prophylaxis regiments. One regimen comprised an intraoperative injection of 5,000 units of subcutaneous unfractionated heparin, pneumatic compression devices, early postoperative ambulation, and routine anticoagulation in the form of LMWH 40 units twice a day. If the BMI was above 50kg/m2, the patient received 60 units of LMWH twice a day and an extended course of LMWH for two weeks postoperatively. For high-risk patients, an IVC filter was placed prior to surgery, and they received 5,000 units of unfractionated heparin and application of pneumatic compression devices pre- and post surgery. No extended LMWH was given in this high-risk group.
Inferior vena cava filters. Inferior vena cava filters have also been recommended for use in high risk bariatric patients (i.e., BMI >55kg/m2, immobility, venous stasis, pulmonary hypertension, hypercoagulability and a history of VTE).
Currently, the literature regarding the indications, risks, and benefits of IVC use in patients undergoing bariatric surgery are not definitive. Studies by Obeid et al and Trigilio-Black et al suggest a decreased rate of PE and death in patients receiving prophylactic IVC filters, whereas other studies have demonstrated a higher complication rate and risk of death attributable to device-related complications. Table 1 provides a summary of current literature[8,13,21,30–33] regarding the use of IVC filters in bariatric patients. Recent recommendations by the American Society for Metabolic and Bariatric Surgery suggest the use of IVC filters, as the only method of VTE prophylaxis is not recommended.
Pulmonary embolism is a leading cause of mortality among high-risk patients undergoing bariatric surgery. In certain situations, such as the trauma setting, IVC filters have been shown to be effective in the reduction of PE. The use of IVC filters has been advocated in the high risk bariatric patients. In some institutions, IVC filters are placed routinely in bariatric patients who meet certain criteria signifying them as high-risk for VTE. Criteria include poor mobility, history of DVT, venous disease, history of PE, bronze skin changes of lower extremity, pulmonary compromise, and BMI over 60kg/m2.[13,21] However, it is important to note that no published data exist regarding the relative incidence of DVT or PE in low- and high-risk bariatric patients.
The pathogenesis of VTE in the patient with morbid obesity is based upon the theory of Virchow’s Triad, which includes three factors: hypercoagulability, hemostasis, and vascular endothelial injury. At least one of these risk factors can be noted in over 90 perent of patients who develop documented VTE.[2,14,24–27] Obesity itself has also been suggested to be a significant independent risk factor for VTE.[2,24] Obesity potentiates biochemical changes, such as increased levels of plasminogen activator inhibitor-1 (PAI-1).[25,26] Plasminogen activator inhibitor-1 decreases the fibrinolytic activity by blocking the conversion of plasminogen to plasmin, thus creating a hypercoagulable state and an increased risk for VTE.[25,26]
Increased levels of leptin and fibrinogen have also been documented in the obese population. Leptin has been shown to increase the expression of PAI-1 in coronary artery endothelial cells in vitro. Hyperfibrinogenemia, which has been noted in obese patients, is strongly associated with an increased risk of VTE due to elevated levels of fibrinogen which lead to increased levels of fibrin and thrombosis.
In addition to the physiologic changes noted in obese patients, bariatric surgery itself increases the risk of VTE. Reverse Trendelenburg positioning and the pneumoperitoneum utilized during laparoscopy decreases the venous return to the heart, which further potentiates the prothrombotic state. The postoperative sequale of pain and poor ambulation further increases VTE risk. However, it should be noted that when using bariatric surgery as the baseline for VTE incidents, Mukherjee et al found that the odds of developing a VTE were higher in bariatric surgery compared to other abdominal surgery, such as colorectal surgery (1.87; p <0.001), pancreatectomy (2.07; p <0.001), gastrectomy (2.44; p <0.001), esophagectomy (2.47; p<0.001), hepatectomy (2.55; p <0.001), and splenectomy (2.69; p <0.001).
The greatest challenge facing the prevention and treatment of VTE in bariatric patients is the lack of class I evidence. The difficulty arises in the dearth of randomized, controlled studies evaluating the various types of preventative measures available during bariatric surgery. Though no class I evidence exists that can definitively provide recommendations regarding the type or duration of VTE prophylaxis in bariatric patients, the ASMBS did provide the following recommendations in a 2013 publication. Their statement position is summarized in Table 2.
The risk of VTE in bariatric surgical patients is omnipresent. However, a consensus VTE prophylaxis still remains elusive as we attempt to determine the safest, most effective means to prevent VTE. Recommendations by the ASMBS should be used by surgeons as a guideline to make the best clinical decision for their bariatric patients as they see fit until randomized, controlled clinical trials can be conducted.
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FUNDING: No funding was provided.
DISCLOSURES: The author reports no conflicts relevant to the content of this article.