Background: On the one hand, according to the obesity paradox, patients with excessive BMI will have lower mortality after onset. On the other hand, due to higher levels of glucose induced by excessive BMI, they will suffer a worse prognosis. This is contradictory. In the present study, we aim to prove the obesity paradox in critically ill stroke patients and find out the potential role of increased glucose.
Methods: This was a retrospective observational study about patients with acute stroke in the intensive care unit (ICU) and all data were extracted from the Medical Information Mart for Intensive Care III (MIMIC-III) database. The main exposure was BMI classified into normal group (18.5≤ BMI<25), excessive group (BMI≥ 25). The outcome concluded 30-day, 90-day and 1-year mortality. The association between two BMI groups and mortality was elucidated by Cox regression models, propensity score matching (PSM) and inverse probability of treatment weighting (IPTW). The underlying effect of blood glucose on the “obesity paradox” was analyzed by causal mediation analysis.
Results: A total of 522 patients were included in our study, of which 177 were the normal group and 345 were the excessive group. According to Cox regression models, a significant beneficial effect of excessive BMI in terms of mortality was observed: 30-day mortality (HR 0.57, 95%CI 0.35-0.90, p = 0.017), 90-day mortality (HR 0.53, 95%CI 0.36-0.78, p = 0.001) and 1-year mortality (HR 0.65, 95%CI 0.46-0.91, p = 0.013). The conclusions were stable after propensity score matching and inverse probability of treatment weighting. There were no interactions between BMI, gender, age, and diabetes. The causal mediation analysis showed that the increased glucose level would reduce the protective effect of excessive BMI on 30-day mortality.
Conclusions: In severe stroke patients, those with excessive BMI are linked to lower mortality, while the protective effect on 30-day mortality weakened accompanied by the acute increase of glucose level.