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Body mass index (BMI) is a measure of body fat calculated by dividing weight by thesquare of height. Since the index was devised by Adolphe Quetelet and is defined by dividingone’s body mass by the square of one’s height (kg/m2), BMI has been commonlyused as proxy measure of excess body fat.According to the literature, higher BMI was strongly associated with higher mortalityin the general population.[1-4] However, critically ill patients’ relative mortality risksassociated with overweight or obesity are still subject to debate although underweighthas been established as a strong predictor of their deaths.[5-8]Several large-scale prospective studies have assessed the association between BMIand mortality in critically ill patients using (identical) cut off values. However, most ofthese studies were conducted on western populations.[9,10] The results of these studiescannot be generalized to Asian populations because of variations in body compositionsand body fat distribution. Indeed, Asians have lower BMI but higher levels of body fatthan Caucasians.[11]In the local research context, Lim SY et al claimed that BMI was not significantly associatedwith mortality in critically ill patients and that mortality risk in critically ill patientswas more associated with failed extubation and severity of illness.[8] In their retrospectivestudy, BMI values were classified into three categories: underweight <18.5;normal weight=18.5-24.9 and overweight/obesity ≥25 kg/m2) for analysis.Recently, a prospective multicenter cohort study was also conducted to evaluate theprognostic performance of the Simplified Acute Physiology Score 3 in 3,655 criticallyill patients in 22 different intensive care units in Korea.[12] Those patients were dividedinto five groups using the cut-off values: <18.5, 18.5-22.9, 23.0-24.9(reference category),25.0-29.9, and >30.0 kg/m2). Their findings showed that the Cox-proportionalhazard ratios with exact partial likelihood to handle tied failures for hospital mortalitycomparing the BMI caretories with the reference category were 1.13 (0.88 to 1.44), 1.03(0.84 to 1.26), 0.96 (0.76 to 1.22), and 0.68 (0.43 to 1.08) respectively, none of whichwere statistically significant. Nonetheless, a graded inverse association between BMIand mortality rate was evident. In other words, the lowest mortality rate was observedin the highest BMI group when surgical patients were excluded, and their findings werefurther explained by experimental evidence that adipocyte-secreted hormones such as interleukin-10[13] and leptin[14] decrease the inflammatoryresponse and improve survival by regulating the immunesystem. Thus excess fat tissue can reduce the risk of complicationsthat protein-catabolic critically ill patients candevelop.Another study also suggested the inverse relationship betweenBMI and mortality risk showing a greater mortalityrisk in the group with BMI of 22.6-27.5.[2] While the prevalenceof obesity is rising worldwide, obesity is consideredone of the most serious public health challenges. Obesity iseven defined as a chronic disease based on its physiologicaldisturbances and potential of causing other serious healthproblems. However, the independent prognostic role of obesityin development of disease and outcomes is still poorlyunderstood.To establish BMI as an independent predictor of increasemortality in critically ill patients, we need to pay more attentionto the trend of increasing obesity and allocate moreeffort to studying relevant issues.
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