Impact of body mass on incidence and prognosis of acute kidney injury requiring renal replacement therapy

In patients with chronic kidney disease, survival has been shown to be better with increasing body mass, an observation which was termed the "obesity paradox". To investigate if such an effect would also be present in patients with acute kidney injury (AKI), we analysed the impact of body mass on the prognosis of intensive care patients with severe AKI requiring renal replacement therapy. A total of 5,232 patients with AKI requiring renal replacement therapy from 53 Austrian ICUs were analysed. Patients were divided into one of five BMI groups: underweight, normal, overweight, obese and morbid obese. The incidence of AKI increased with increasing body mass from underweight, normal (5.4%) to morbid obese (11.8%). Moreover, adjusted odds ratios to develop AKI were significantly increased for all groups (reference group: normal). Risk-adjusted hospital mortality rates followed a U-shaped pattern, with the lowest mortality in obese patients (BMI of a parts per thousand yen 30 < 35). Multivariate analysis (with adjustment for severity of illness, sex, reason for admission and comorbidities) confirmed these results: obese patients presented with a significantly reduced probability to die in the hospital [odds ratio 0.81 (0.66-0.98)]. Obesity is an independent risk factor for developing AKI. Our results provide further evidence that body mass impacts on survival of patients with AKI requiring renal replacement therapy. Obese patients seem to have a survival benefit compared to underweight or normal weight patients.