Background: The Obesity Paradox postulates that obesity is a protective factor against mortality in certain chronic conditions such as chronic kidney disease (CKD) and congestive heart failure. Although this paradox is established in CKD, few studies have analyzed the paradox in acute kidney injury (AKI). There are both short and long term ramifications to AKI such as increased length of hospital stay (LOS) and mortality, respectively. This study’s objective is to correlate obesity with post-surgical AKI and the sequelae of length of hospital stay and 2-year mortality rate in adult elective orthopedic patients.
Methods: We retrospectively reviewed the electronic medical records of all adult elective orthopedic surgery patients over two years in a large academic hospital. The 1783 patients who met inclusion criteria were divided into obese (body mass index, BMI ≥ 30, n=1123) and non-obese groups (BMI < 30, n=660). Demographics, comorbidities, and perioperative variables were included in multivariate logistic regression analyses with AKI, LOS, and two year mortality as primary outcomes in all, obese and non-obese patients. Two-year mortality data was obtained from hospital electronic records and the social security death index.
Results: AKI developed in 5% (n=90) of the post-surgical orthopedic patients. Obese patients had a 1.86 times higher odds (95% CI 1.07-3.22, p=0.028) of developing AKI than non-obese patients. AKI increased length of hospital stay in both obese (1.28±0.38 days, p=0.001) and non-obese patients (1.61±0.78 days, p=0.039). AKI also increased odds of 2-year mortality (OR 2.08, 95% CI 1.03-4.22, p=0.041) while obese patients had decreased mortality odds (OR 0.53, CI 0.33-0.85, p=0.009). Of patients who developed AKI, only the non-obese patients had statistically significant higher likelihood of 2-year mortality (OR 3.869, CI 1.26-11.84, p=0.018).
Conclusions: In adult elective orthopedic surgery patients, obese patients had an increased risk of AKI, and patients who developed an AKI had longer hospital stays. However, obesity was a protective factor for 2-year mortality for all post-surgical patients including patients who developed an AKI.