We conducted a retrospective single-center study to analyze the association between obesity and postoperative adverse outcomes following EL for high-risk abdominal emergencies. We found that patients with obesity had significantly higher rates of complications and mortality than nonobese patients. Comorbidities, morbidity and mortality were lowest in the normal-weight group.
Our findings suggest that BMI is an important clinical factor that influences outcomes in high-risk abdominal emergency patients undergoing surgery that cannot be personalized and optimized to their weight in emergency situations.
Almost all postoperative-specific complications were found to have increased rates among patients with obesity. Other studies also support that obesity is associated with an increased complication rate in surgical patients. Giles et al. [17] studied patients undergoing aortic aneurism repair and showed that the rate of complications was 2 times higher in patients with obesity than in normal-weight patients, and patients with obesity had significantly higher mortality. Liu et al. [18] performed a systematic review of studies in trauma patients and showed that obesity was associated with increased risks of postoperative complications and mortality. For general surgery procedures, Yanquez et al. [19] found an increased risk of complications in patients with obesity.
The comorbidity rate was significantly higher in patients with obesity than in normal-weight patients. In a separate analysis, many of the comorbid conditions predicted the risk of specific postoperative complications. In decreasing order of value, these factors included URL, liver cirrhosis, PAD, ASA class ≥ 3, age ≥ 70 years, atrial fibrillation, chronic heart failure, chronic renal failure, BMI, and hypertension. In the multivariable logistic regression analysis, age, ASA, PAD, liver cirrhosis and URL remained significant predictors of complications. It is widely accepted that BMI above the normal range affects many comorbid conditions, particularly cardiovascular and renal diseases [3, 4]. Thus, by extension, the increased complication rate observed in our study seems to be a sequela of comorbid conditions associated with obesity. Furthermore, patients with obesity undergoing surgery for high-risk abdominal emergencies required prolonged mechanical ventilation, defined as postoperative intubation for longer than 24 h, and thus a prolonged bedridden hospital stay. Therefore, these patients are likely to develop complications that subsequently contribute to mortality. This is in agreement with the results of other studies that reported an increased frequency of prolonged ventilation in obese patients undergoing elective surgical procedures [20]. The incidence of pneumonia did not differ between obese and normal-weight patients; however, postoperative respiratory impairment that resulted in ICU admission was frequent in patients with obesity, similar to the findings of other researchers [21].
Specific data on outcomes after surgery for high-risk abdominal emergencies were not available. In a relatively small retrospective study, Ferrada et al. [22] found no significant increase in mortality in patients with obesity undergoing emergency surgery. Although a consensus definition of obesity has been established by the WHO, these authors defined patients as nonobese and obese and included underweight patients in the nonobese and overweight patients in the obese group without accurate categorization of patients according to their BMI. Mortality in patients with obesity following emergency surgery cannot be analyzed in this context, as the occurrence of major adverse events differs based on BMI.
In contrast, the previously reported finding that patients with obesity suffer a higher rate of mortality in aortic repair [17], trauma [18], and elective general surgeries [23] was verified in our analysis of high-risk abdominal emergency patients. This demonstrated that in-hospital mortality in patients undergoing EL for high-risk emergencies varied by weight classification. There was a gradual increase in mortality with increasing weight class, where patients with BMI ≥ 40 fared the worst. This indicates that even small changes in weight can affect outcomes. Our multivariate regression analyses of the factors identified to be significantly different in obese patients found that the ORs for pneumonia, anastomotic leakage, acute renal failure and liver failure were 2.9, 5.5, 8.3 and 34.5, respectively. It is likely that these complications are responsible for the absolute excess mortality in patients with BMI ≥ 30. However, we cannot infer a causal relationship with these data.
The operative time and LOS were longer, and the ICU admission rate was higher in patients with obesity than in normal-weight patients. This indicates that in addition to its clinical significance in morbidity and mortality, obesity may have a widespread impact on overall treatment cost. Therefore, although impossible to implement in emergency situations, optimizing nutrition and weight in the general population would have a decisive role in minimizing complications and cost-related variables, such as LOS, and indirectly improve outcomes (in the long term), even in patients undergoing surgery due to high-risk emergencies.
The underlying mechanisms of these adverse events (i.e., morbidity and mortality) following surgery for high-risk abdominal emergencies are not entirely clear; however, there is evidence that energy use in patients with obesity, especially those in the higher BMI category (BMI ≥ 35; 40% of our patients with obesity), is inefficient, and underlying metabolic excess leads to hyperbolic inflammatory responses, oxidative stress, and further metabolic dysfunction and immunosuppression. As a result, these patients are not fit to handle the extreme stress imposed by surgery in emergent situations and thus experience more adverse events [9, 24, 25].
Overall, our results suggest that BMI itself was not an independent factor predictive of in-hospital mortality following EL for high-risk abdominal emergencies. However, the percentage of every analyzed comorbid condition and complication tended to increase with increasing BMI and there was a gradual increase in mortality with increasing weight class, where patients with BMI ≥ 40 fared the worst. Therefore, obesity may predispose patients to mortality through its impact on numerous coexisting conditions and postoperative complications following EL for high-risk abdominal emergencies. The lack of a significant statistical association between increasing BMI and in-hospital mortality in the multivariate model probably reflects the relatively small sample size, especially in the highest BMI categories, rather than biologic reality.
Compared to recent data in the literature [26, 27] that reported on the association of obesity with morbidity and mortality in trauma patients, the mortality rate in our cohort was notably high. Given the very different risk profiles for complications and mortality of trauma patients, however, the high mortality rate indicated in this study is relative and attributable to the risk-based approach of patient selection. In trauma patients, the injury mechanism to the abdomen is either blunt or penetrating. We included only consecutive multimorbid patients with high-risk emergencies, such as mesenteric ischemia and viscous organ perforation, mostly related to chronic illnesses, where the acute insult is greater. These patients are at high risk of procedural adverse events and tend to have septic complications with multiple organ dysfunction that inevitably lead to death [28, 29]. If we consider our entire primary emergency cohort including those patients with minor emergencies, the overall mortality rate is less than 15%, which is within the range of mortality rates reported in the literature [30,31,32].
Our study has limitations that are inherent to a retrospective study. First, this was a retrospective study and was therefore subject to reviewer error and data miscoding, and certain details important to the analysis of outcomes were missing. We did not include lifestyle factors such as smoking, alcohol consumption, lack of physical activity, dietary factors and medication compliance in the analysis, which could have provided alternative explanations for our findings; unfortunately, data on these variables were not consistently recorded in our database. Second, our study was a single-center study; our findings may therefore not be generalizable to other centers and institutions at large. Finally, we categorized BMI into underweight, overweight and obese using normal-weight patients as the reference group, but a detailed statistical analysis for underweight patients was not performed. In addition to focusing on obese patients, delineating underweight patients is necessary in the identification of major outcomes because underweight is associated with additional individual health risks. However, the approach we undertook was necessary owing to the small sample size in the underweight group (only 50 patients), which would have limited the statistical power.
Despite these limitations, our study provides an important evaluation of the impact and outcomes associated with obesity in a population of patients undergoing surgery due to high-risk abdominal emergencies.