Synergistic effect of age and body mass index on mortality and morbidity in general surgery.
BACKGROUND
The elderly population (aged 65 y and older) is expected to be the dominant age group in the United States by 2030. In addition, the prevalence of obesity in the United States is growing exponentially. Obese elderly patients are increasingly undergoing elective or emergent general surgery. There are few, if any, studies highlighting the combined effect of age and body mass index (BMI) on surgical outcomes. We hypothesize that increasing age and BMI synergistically impact morbidity and mortality in general surgery.


MATERIALS AND METHODS
We collected individual-level, de-identified patient data from the Michigan Surgical Quality Collaborative. Subjects underwent general surgery with general anesthetic, were >18 y, and had a BMI between 19 and 60. Primary and secondary outcomes were 30-d "Any morbidity" and mortality (from wound, respiratory, genitourinary, central nervous system, and cardiac systems), respectively. Preoperative risk variables included diabetes, dialysis, steroid use, cardiac risk, wound classification, American Society of Anesthesiology class, emergent cases, and 13 other variables. We conducted binary logistic regression models for 30-d morbidity and mortality to determine independent effects of age, BMI, interaction between both age and BMI, and a saturated model for all independent variables.


RESULTS
We identified 149,853 patients. The average age was 54.6 y, and the average BMI was 30.9. Overall 30-d mortality was 2%, and morbidity was 6.7%. Age was a positive predictor for mortality and morbidity, and BMI was negatively associated with mortality and not significantly associated with morbidity. Age combined with higher BMI was positively associated with morbidity and mortality when the higher age groups were analyzed. Saturated models revealed age and American Society of Anesthesiology class as highest predictors of poor outcomes.


CONCLUSIONS
Although BMI itself was not a major independent factor predicting 30-d major morbidity or mortality, the morbidly obese, elderly (>50 and 70 y, respectively) subgroup may have an increased morbidity and mortality after general surgery. This information, along with patient-specific factors and their comorbidities, may allow us to better take care of our patients perioperatively and better inform our patients about their risk of surgical procedures.
['Yanquez|Federico J|FJ|', 'Clements|John M|JM|', 'Grauf|Dawn|D|', 'Merchant|Aziz M|AM|']
D000328:Adult D017677:Age Distribution D000368:Aged D000369:Aged, 80 and over D015992:Body Mass Index D016208:Databases, Factual D017558:Elective Surgical Procedures D005260:Female D013502:General Surgery D006801:Humans D016015:Logistic Models D008297:Male D008824:Michigan D008875:Middle Aged D009017:Morbidity D009765:Obesity D009767:Obesity, Morbid D011183:Postoperative Complications D015995:Prevalence D011787:Quality of Health Care D012307:Risk Factors
Age Mortality Morbidity BMI Surgical outcomes Elderly obese Michigan Surgical Quality Collaborative Administrative database Morbid obesity