Use of sarcopenia to predict risk of mortality after emergency abdominal surgery in elderly patients

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To the Editor:
With great interest, we read the recent article by Rangel and colleagues1 regarding the use of sarcopenia to predict the risk of postoperative mortality in elderly patients undergoing emergency abdominal surgery. By the Cox proportional hazards regression analysis, they showed that sarcopenia defined by total psoas index was associated with increased risks of mortality over 1 year. Other than the limitations described in the discussion section of Rangel and colleagues'1 article, however, we noted that several issues of this study were not well addressed.
First, sarcopenic and nonsarcopenic patients were comparable with respect to age, sex, race, Charlson comorbidity index, American Society of Anesthesiologists physical status classifications, prevalence of emergency cases, operative severity, and type of procedure, but sarcopenic patients were more likely to require intensive care unit care after surgery. The readers were not provided with detailed reasons for intensive care unit admission of patients. Most importantly, it was unclear whether sarcopenic and nonsarcopenic patients were comparable in postoperative complications. The available literature shows that postoperative complications, such as stroke, sepsis, myocardial infarction, acute kidney injury, and pulmonary complications, are significantly associated with mortality after emergency surgery.2,3 Furthermore, there are interaction effects between certain complications to increase the risk of postoperative mortality. Especially, pulmonary complications, acute kidney injury, sepsis, and stroke are most likely to be involved in positive interactions. Thus, we are concerned that any unbalance in postoperative complications between sarcopenic and nonsarcopenic patients would have biased the association between sarcopenia and postoperative mortality obtained by the Cox proportional hazards regression model in this study.4
Second, in the statistical analysis section, the authors described that model performance was assessed by Harrell's concordance index (C-index) and the area under the receiver operating characteristic (ROC) curve. However, the readers were not provided with the results of the ROC curve analysis. Actually, to determine predictive ability of sarcopenia for increased risk of postoperative mortality, providing only the C-index is not enough. By constructing the ROC curve and performing the ROC curve analysis, sensitivity, specificity, and positive and negative predictive values of sarcopenia for increased risk of postoperative mortality can further be obtained.
Third, other than sarcopenia, this study showed that Charlson comorbidity index of 4 or greater, major operative severity, and American Society of Anesthesiologists physical status classifications 3 and 4 were also the independent predictors of mortality over 1 year after surgery. However, the readers were not provided with the C-indexes of these predictors for increased risk of postoperative mortality. Thus, it is unclear whether predictive performance of sarcopenia for increased risk of postoperative mortality in elderly patients undergoing emergency abdominal surgery equals or surpasses these risk scores.
Fourth, this study had actually assessed predictive ability of sarcopenia for increased risk of early- and late-term postoperative mortality. The available evidence indicates that there are significant differences in mortality risk factors between early and late periods after surgery. The early-term mortality is most likely related to the surgery and perioperative management and lasts approximately a month. However, the late-term mortality primarily represents the natural process of aging or potential diseases.5 Perhaps, this is a possible reason for the finding of this study that predictive performance of sarcopenia for postoperative mortality is different between early and late periods; namely, the hazard ratios are greatest at 30 days and declined thereafter.
Finally, according to the findings of this study, it would be better that the title of this article is changed to “Sarcopenia Increases the Risk of Mortality Over 1 Year After Emergency Abdominal Surgery in Elderly Patients.
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