EP790 - Estimating The Causal Effect Of Obesity On IPAA Construction Using NSQIP Database

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Purpose/Background: Body mass index (BMI) is a known modifiable risk factor in patients receiving ileal pouch anal anastomosis (IPAA). By looking at BMI as a continuous variable, we target a more optimal BMI range to reduce serious postoperative complications after IPAA.

Methods/Interventions: We performed a retrospective analysis of ileal pouch anal anastomosis (IPAA) surgeries (CPT codes 44211, 44158, and 45113) from the NSQIP database from 2018-2021. In total, there were 2340 records analyzed. Within this database and using a causing inference framework, we evaluated the impact of BMI on five outcomes: operation time, length of stay, discharge disposition, readmission, and post operative complications based on Clavien-Dindo grades (1-5). Non-linear causal effects of BMI were estimated with exposure response functions and G-computation. The covariates include age, sex, race, diagnosis type (malignancy, IBD, benign neoplasm/polyposis, other), surgery type (CPT codes), ASA class (1/2 vs 3/4), and comorbidities (smoking, diabetes, and hypertension).

Results/Outcomes: Preliminary analyses show that BMI had a non-linear effect on both operation time and length of stay, such that there were exponential increases for BMIs between 30-36. There was no impact of BMI on discharge disposition. We found that the extreme ends of BMI were different in the probability of obtaining a 3 or higher Clavien-Dindo grade with respect to a reference BMI of 22, which had the lowest probability. Patients with a BMI of 22 had a 16.9% lower Clavien-Dindo complication rate (>=grade 3) than patients with a BMI of 18. Patients with a BMI of 35 had a 9.2% higher Clavien-Dindo complication rate (>=grade 3) compared to patients with a BMI of 22

Conclusion/Discussion: Constructing an IPAA is an immense undertaking for which the first attempt is typically the best chance for long-term intestinal continuity, desired functional outcome, and low morbidity. Therefore, it is imperative to address preoperative risk factors as aggressively as possible to mitigate risk of serious postoperative complications. Obesity is a known risk factor for intraoperative difficulties and postoperative complications that we believe can be modified in the preoperative setting. This retrospective analysis highlights the positive correlation of higher BMI and longer operating room time. It also highlights how the probability of a serious complication (Clavien Dindo >/= 3) is not only exacerbated by the class of obesity, but on the other end of the spectrum, having a relatively low BMI.

Although isolated BMI is an imperfect marker for surgical risk, it is an acceptable surrogate for discussion in the context of a patient’s nutritional status, which is vital to the healing of a pouch-anal anastomosis. Furthermore, the majority of prior studies correlating BMI and pouch complications looked at BMI as a categorical variable. When looking at BMI as a continuous variable, we identify a more accurate, lower risk BMI range to proceed with pouch construction that is more specific than the conventional nomenclature quantifying BMI as “underweight”, “healthy weight”, “overweight”, and “obese”. This newly identified BMI range may help guide timing of future pouch construction surgery to allow nutritional and BMI goals to be met, as well as influence the staging approach to IPAA construction (1-,2-, modified 2-, and 3-stage). It is plausible that delaying pouch construction for patients to achieve a BMI closer to 22 would reduce the probability of serious pouch complication and the lifelong consequences that accompany them.