How apt that this morning I watched one of my favourite episodes of “The Simpsons,” “King-Size Homer” from series 7, in which Homer gains 60 Lbs in order to reach 300 Lbs, allowing him to work from home on a disability scheme. As always, The Simpsons provide a very accurate commentary on modern society, in this case the obesity epidemic. The episode contains one of my all time favourite lines from a Simpsons episode; when Homer is refused entry to the movie “Honk if you’re Horny” on account of the cinema seats being inadequate for his girth, a fellow movie-goer jibes “Hey, fatty. I’ve got a movie for ya – A fridge too far!”
Anyway, what does this have to do with intensive care. Well an early release article appeared the other day in “Critical Care” that caught my eye. Abhyankar et al retrospectively reviewed a large ICU database from a single hospital in Boston, MA. Sounds dodgy, but the database had 16,812 patients covering a 7 year period from 2001-2008. Some of the over 25,000 patients in the MIMIC database were excluded (children, no weight available) leaving 16,812 for analysis.
The authors compared 30 day and 1 year all cause mortality with BMI, using the standard WHO categories of underweight (<18.5), normal weight (18.6-25), Overweight (25-30) and Obese (>30). They controlled for SAPS score, comorbidities, gender, insurance status, and ethnicity. Height wasn’t available for 25% of patients, so they had a height allocated based on their other demographic factors. The final analysis was conducted with and without these patients.
The results were pretty impressive. OR for mortality in overweight patients was 0.81 at 30 days and 0.68 at one year. Even more impressive were the results for obese patients, OR for death 0.74 at 30 days, 0.57 at one year. So if you’re obese you’re almost half as likely to die following an ICU admission than someone who is normal weight. Of note, the survival advantage disappears for the very obese (BMO >40). Results were all significant.
I think that the authors did a pretty good job controlling for potential confounders like diabetes, obesity related cancers, age, SAPS score, etc. The results were also similar when the 25% with guessed heights were removed.
So what’s going on? The authors have a couple of hypotheses. One is related to immunomodulatory effects of apidocytes. The other is a bit more simple – overweight and obese people have more nutritional reserves, giving them a survival advantage.
So perhaps one of the most effective lifesaving tools that we have in the ICU is a bucket of fried chicken…?
The paper is open access, so have a look for yourself. Here’s the abstract if you’re short of time.
Lower short- and long-term mortality associated with overweight and obesity in a large cohort study of adult intensive care unit patients
Swapna Abhyankar, Kira Leishear, Fiona M Callaghan, Dina Demner-Fushman and Clement J McDonald
Critical Care 2012, 16:R235
Published: 18 December 2012
Two-thirds of U.S. adults are overweight or obese, which puts them at higher risk of developing chronic diseases and of death compared to normal weight individuals. However, recent studies have found that overweight and obesity by themselves may be protective in some contexts, such as hospitalization in an intensive care unit (ICU). Our objective was to determine the relationship between body mass index (BMI) and mortality 30 days and one year after ICU admission.
We performed a cohort analysis of 16,812 adult patients from MIMIC-II, a large database of ICU patients at a tertiary care hospital in Boston, Massachusetts. The data were originally collected during the course of clinical care, and we subsequently extracted our dataset independently of the study outcome.
Compared to normal weight patients, obese patients had 26% and 43% lower mortality risk at 30 days and one year after ICU admission, respectively (OR 0.74 [95% CI, 0.64-0.86] and 0.57 [95% CI, 0.49-0.67]); overweight patients had nearly 20% and 30% lower mortality risk (OR 0.81 [95% CI, 0.70-0.93] and 0.68 [95% CI, 0.59-0.79]). Severely obese patients (BMI [greater than or equal to]40 kg/m2) did not have a significant survival advantage at 30 days (OR 0.94 [95% CI, 0.74-1.20]), but did have 30% lower mortality risk at one year (OR 0.70 [95% CI, 0.54-0.90]). There was no significant difference in admission acuity or ICU and hospital length of stay across BMI categories.
Our study supports the hypothesis that patients who are overweight or obese have improved survival both 30 days and one year after ICU admission.