Introduction
Generally, elderly patients have a high incidence of comorbidity (9.0–52.5%) and are usually considered a high-risk group for hepatectomy [
1,
2]. According to a report of the Japanese Nationwide Survey on hepatocellular carcinoma (HCC) resection, elderly patients had significantly worse overall survival probabilities than younger patients (the 5-year overall survival probabilities: 68.8% vs. 59.5%; hazard ratio: 0.76). Furthermore, the cumulative incidence of HCC- or liver-related death was almost identical between elderly and younger patients, though the cumulative incidence of other causes of death was higher in the elderly (subdistribution hazard ratio: 0.32) [
3]. For example, preoperative frailty in elderly patients undergoing hepatectomy is associated with age-related events such as cardiopulmonary complications, delirium, transfer to a rehabilitation facility, and dependency [
4]. Thus, the indication of hepatectomy for elderly patients should be considered based on not only the tumor condition and liver function but also the risks specific to elderly patients.
However, predicting postoperative risk in elderly patients undergoing hepatectomy is not easy because of the lack of a reliable preoperative evaluation system. For example, estimation of physiological ability and surgical stress (E-PASS) [
5] and physiological and operative severity score for the enumeration of mortality and morbidity (POSSUM) scores [
6] have been reported previously for predicting postoperative complications in elderly patients with HCC. However, these systems are complicated and not specific for the elderly or hepatectomy. Simons et al. also reported an original risk score of in-hospital mortality for HCC resection [
7]; however, this score cannot predict postoperative complications.
Therefore, we aimed to establish a new simple preoperative evaluation system for predicting postoperative complications in elderly patients undergoing elective hepatectomy. Biological impedance analysis (BIA), which is different from tests for the evaluation of tumor condition or liver function, was introduced in this study to evaluate patients’ preoperative body composition. BIA can be used to measure body water content, muscle mass, and fat mass using electrical impedance [
8] and to diagnose decreased skeletal muscle, which is an element of sarcopenia and an important prognostic factor for hepatectomy for both HCC [
9] and colorectal liver metastasis [
10].
Discussion
The present study revealed that preoperative decreased skeletal muscle and the type of surgical procedure used for hepatectomy appeared to have a statistically significant impact on the Clavien-Dindo ≥ III postoperative complications among patients aged 65 years or older undergoing hepatectomy. In this report, the preoperative risk assessment of the elderly undergoing hepatectomy is discussed from a new perspective using BIA.
Recently, sarcopenia has increasingly been recognized as an important factor in predicting postoperative complications and long-term prognosis among patients undergoing gastrointestinal surgery [
20]. Decreased skeletal muscle is an important element of sarcopenia. The guidelines from the American College of Surgeons have also highlighted the importance of assessing sarcopenia before surgical oncology in the elderly [
21]. Valero et al. showed that a low preoperative psoas muscle mass is an independent risk factor for postoperative complications in patients with Clavien-Dindo ≥ III undergoing hepatectomy and liver transplantation for HCC [
22]. Higashi et al. similarly reported that sarcopenia is a risk factor for postoperative complications in patients undergoing major hepatectomy. They also mentioned that sarcopenia is a risk factor for liver-related morbidity and mortality in patients aged > 70 years [
23]. According to another report, low skeletal muscle mass and quality are also related to mortality after resection of intrahepatic cholangiocarcinomas [
24]. Thus, sarcopenia or decreased skeletal muscle is a risk factor for hepatectomy, though it has not been used as an item of preoperative risk index before.
In the present study, we used the BIA for diagnosis of decreased skeletal muscle mass. BIA can be used to evaluate the body composition precisely by calculating the electrical impedance of a patient’s body. The usefulness of the BIA has already been confirmed widely in liver cirrhosis [
25] and living donor liver transplantation patients [
26]. However, in almost all of the previously cited reports, the psoas or skeletal muscle mass was calculated either using L3-level computed tomography (CT) or magnetic resonance imaging (MRI). The area of skeletal muscle at the L3 level was directly correlated with whole-body skeletal muscle [
27]. This method had the advantage that most of our hepatectomy patients underwent CT or MRI preoperatively, meaning that there was no need for performing other tests. These methods approximate the BIA, though they can be used as a substitute for BIA, especially when an institution lacks BIA equipment. However, the BIA has the disadvantage that the optimal cut-off values for SMI in the elderly population have not been determined. Because of the lack of optimal cut-off values of SMI in both the elderly population and in hepatectomy patients, the AWGS criteria were used in this study. Further studies will be needed to determine the optimal cut-off value, especially in elderly patients.
Furthermore, there are some reports on the relationship between body composition (other than muscle mass) and postoperative complications in hepatectomy. Low preoperative body cell mass is a risk factor for infections associated with mortality in cases of living donor liver transplantation [
26]. In line with this study, we evaluated the body cell mass, though no significant difference was observed in our study cohort. Hamaguchi et al. reported that preoperative muscle steatosis in patients undergoing hepatectomy for HCC is an independent risk factor for postoperative complications in patients with Clavien-Dindo ≥ III and infectious complications [
28]. In another study, it was reported that a low preoperative SMI value, high intramuscular adipose tissue content, and high visceral-to-subcutaneous adipose tissue-area ratio were risk factors for mortality and recurrence in patients undergoing hepatectomy for HCC [
29]. In this study, only total body fat was evaluated, with no significant difference observed in this parameter.
Serum albumin was previously shown to be an independent risk factor for postoperative complications in elderly patients undergoing hepatectomy [
5]. Therefore, the preoperative serum albumin levels, in addition to the SMI value and the type of surgical procedure, were also included in the development of the new preoperative risk score for predicting postoperative complications. Based on these three items, we developed a new, simple preoperative risk score for elderly patients who underwent elective hepatectomy. There are already some other established risk assessment systems. For example, the ACS NSQIP surgical risk [
16], E-PASS [
17], POSSUM [
18], and P-POSSUM [
19] also showed relatively good results with significant differences in ROC analysis for predicting postoperative complications. However, our risk score showed better results and may be simpler and easier to use than these other risk assessment systems. Additionally, our risk score may have better performance than other systems because it focuses on hepatectomy in elderly patients and uses BIA, which has not been used in other systems.
Despite these significant findings, the present study has several limitations. This study was performed in a single center with a relatively small number of patients. Therefore, our risk score should be validated in other subjects in a multicenter study. Further, patients in whom BIA could not be performed, such as those with metal objects inside the body, or those who could not stand unassisted, were excluded from the study. Therefore, our risk score may not be applicable directly for these patients. Evaluation of psoas muscle mass at the L3 level is a possible substitute for BIA, although further studies are needed for confirmation. Also, elderly patients who were deemed too frail for the surgery did not undergo hepatectomy. Therefore, further prospective studies will be needed to exclude this preselection bias.
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