No randomized control trials (RTC) were identified comparing patients with IVC filter and no IVC filter in the population of interest. There were numerous observational studies in the bariatric patient population, both retrospective and prospective [7–22]; (Table 35.2). Most studies are observational and involve small number of patients. These studies include several comparing cohorts with IVC filter to controlled cohorts without. Most studies are either advocating IVC filter use in morbidly obese patients, or neutral about filter use, citing benefit in the prevention of PE, or lack of major complications regarding its use. Gargiulo et al., in a study of 58 patients with IVC filter who underwent gastric bypass surgery, out of a total of 571 morbidly obese patients, showed that 56 patients remained free of VTE, while only one developed a DVT that resolved with treatment [9]. The only mortality was in a patient who required multiple operations from bypass complications and who could not be treated with intravenous heparin, progressed to IVC thrombosis and phlegmasia cerulea dolens requiring bilateral above knee amputations; the patient subsequently died. They concluded that use of IVC filter is benign with maximal benefit in term of PE prevention. Piano et al. reported a prospective observational study of 59 consecutive high risk patients undergoing laparoscopic gastric bypass or duodenal switch [13]. Patients were considered high risk if they met any of these criteria: BMI > 55 kg/m², hypercoagulable state, severe immobility, venous stasis, or previous history of VTE. The mean BMI was 61 ± 10 kg/m². One patient developed PE with filter in place while not on post-operative anti-coagulation and there was no death. The primary retrieval rate was 90 % and 3 patients underwent another attempt and all had successful retrievals. There were no complications with filter placement or retrieval. The authors concluded that use of filters in high risk bariatric patients is safe and offer potential clinical benefit.

A few studies question the efficacy and safety of IVC filter in what is considered high risk patient groups. Li et al. used the Bariatric Longitudinal Database (BOLD), comprised of patients undergoing Roux-en-Y gastric bypass and adjustable gastric banding surgeries [21]. They identified 332 patients (out of 97,218) who had concurrent prophylactic IVC filter placement. For this small group of patients, they had more co-morbidity, including sleep apnea, history of VTE, pulmonary hypertension, and obesity hypoventilation syndrome. This group also had longer length of operative duration and hospital stay, and was associated with higher incidence of DVT and higher mortality from PE and indeterminate causes. The authors summarized their findings as concurrent use of IVC filters was associated with increased health resource utilization and a higher mortality in patients undergoing bariatric operations, and concluded that they were unable to establish an outcome benefit for concurrent IVC filter use.

Birkmeyer et al. looked at a cohort of 1,077 patients with IVC filters and compared them to 1,077 matched control patients out of a database of 35,477 bariatric surgery patients [22]. From this database, they found 95 % of patients in the low-risk group, 4 % in the medium-risk group and 1 % in the high-risk group. In the matched study cohorts the breakdown was 69, 22, and 9 % for high-risk, medium-risk, and low-risk group respectively. They found that compared to their matched cohort using propensity scores, IVC filter patients had higher rates of VTE, higher but not statistically significant rate of PE, and higher rates of surgery related complications. The authors acknowledge limitations of their study including outcomes of interest being a rare event affecting the statistical power, a lack of data on hypercoagulable states in the registry, multitude of IVC filter available with difference in efficacy and safety profile, and the 30-day after surgery endpoint. The authors concluded that, based on their study, IVC filters do not reduce the risk of PE in high-risk bariatric patients and use of IVC filters should be discouraged.