Obesity and the Survival of Critically Ill Patients with Acute Kidney Injury: A Paradox within the Paradox?

The obesity epidemic is reflected by the rising number of obese patients requiring intensive care. Obesity is a recognized risk factor for the development of acute kidney injury (AKI) in critically ill patients. Both acute critical illness and AKI are associated with higher in-hospital mortality rates, and intensive care unit (ICU) patients suffering from AKI have an elevated risk of death. The relationships between obesity and mortality in critically ill paediatric and adult patients with or without AKI are less clear. Conflicting evidence exists regarding the potential impact of body mass index on the mortality of ICU patients with AKI. Some studies looking at the ICU outcomes of critically ill obese patients with AKI show reduced mortality and others show either no association or elevated mortality. Despite a high biologic plausibility of the proposed causal mechanisms, such as a greater haemodynamic stability and the protective cytokine, adipokine, and lipoprotein defence profiles associated with obesity, the inconsistency of the data suggests that the obesity paradox is a statistical fallacy and the result of chance, bias, and residual confounding variables in retrospective cohort analyses. Further prospective randomized trials are essential to elucidate the role of obesity and the mechanisms underlying a potential survival benefit of obesity in critically ill patients with AKI.