Body Mass Index, Outcomes, and Mortality Following Cardiac Surgery in Ontario, Canada

Abstract

BackgroundThe “obesity paradox” reflects an observed relationship between obesity and decreased morbidity and mortality, suggesting improved health outcomes for obese individuals. Studies examining the relationship between high body mass index (BMI) and adverse outcomes after cardiac surgery have reported conflicting results.Methods and ResultsThe study population (N=78 762) was comprised of adult patients who had undergone first-time coronary artery bypass (CABG) or combined CABG/aortic valve replacement (AVR) surgery from April 1, 1998 to October 31, 2011 in Ontario (data from the Institute for Clinical Evaluative Sciences). Perioperative outcomes and 5-year mortality among pre-defined BMI (kg/m2) categories (underweight <20, normal weight 20 to 24.9, overweight 25 to 29.9, obese 30 to 34.9, morbidly obese >34.9) were compared using Bivariate analyses and Cox multivariate regression analysis to investigate multiple confounders on the relationship between BMI and adverse outcomes. A reverse J-shaped curve was found between BMI and mortality with their respective hazard ratios. Independent of confounding variables, 30-day, 1-year, and 5-year survival rates were highest for the obese group of patients (99.1% [95% Confidence Interval {CI}, 98.9 to 99.2], 97.6% [95% CI, 97.3 to 97.8], and 90.0% [95% CI, 89.5 to 90.5], respectively), and perioperative complications lowest. Underweight and morbidly obese patients had higher mortality and incidence of adverse outcomes.ConclusionsOverweight and obese patients had lower mortality and adverse perioperative outcomes after cardiac surgery compared with normal weight, underweight, and morbidly obese patients. The “obesity paradox” was confirmed for overweight and moderately obese patients. This may impact health resource planning, shifting the focus to morbidly obese and underweight patients prior to, during, and after cardiac surgery.

Hydrogen Gas Attenuates Myocardial Ischemia Reperfusion Injury Independent of Postconditioning in Rats by Attenuating Endoplasmic Reticulum Stress-Induced Autophagy

“…What’s more, recent studies indicate that post-ischemic 30 day mortality (about 8.5% after angioplasty and about 14% with thrombolysis) remains high [6]. Lines of studies have demonstrated that myocardial ischemic/reperfusion (I/R) might contribute to reperfusion arrhythmia, myocardial diastolic dysfunction, and irreversibly disordered metabolism and function [7]. …”

Morbid obesity and perioperative complications

“…In light of these limitations, it is difficult to conclusively determine the association between BMI and perioperative mortality. Compared with normal weight patients, at this time the literature suggests a survival benefit in the lower BMI obesity range and worse long-term mortality at the higher BMI ranges (>40 kg/m 2 ) [41,42,44].…”

“…Similarly, multivariate analysis of 78 762 Canadian CABG and combined CABG and aortic valve replacement patients found a survival advantage for patients with a BMI 25-29.9 kg/m 2 and no difference for patients with a BMI 30-34.9 kg/m 2 compared with normal weight patients. Increased mortality was only observed in those with BMI greater than 34.9 kg/m 2 and underweight patients (BMI < 20 kg/m 2 ) [42]. Analysis of 10 427 elective, noncardiac surgery patients in the Netherlands also showed improved long-term mortality in patients with BMI at least 25 kg/m 2 , though this was noted to be because of a strongly reduced risk of cancerrelated death [43].…”

“…Variables with a negative impact on survival, such as positive smoking status, increased age, recent weight loss, and increasing disease severity, are often correlated with a decreased BMI [5,[41][42][43]45], yet are not always accounted for in the analysis of large datasets [43]. Strategies to avoid these confounders are to account for them in multivariate analysis where possible, perform more detailed BMI stratification [45], and limit the analysis of survival data to long-term survival to avoid reverse causation (where decreased BMI itself is not the cause of poor outcomes, but rather is just a marker of the disease severity that results in decreased survival) [42][43][44]. Similarly, it has not been comprehensively determined if the obesity paradox exists with both 'unhealthy' and 'healthy' obesity, that is, obesity with and without associated comorbidities and metabolic syndrome.…”

Impact of Body Mass Index on Outcomes in Cardiac Surgery

“…Although some may postulate that this could be due to the lack of BMI's definition to differentiate between body fat and lean mass, 38 there is no reasonable and definite explanation for these surprising and contradictory results in both this study and the most recent research. 39 …”