In our retrospective study of 1241 patients who underwent colorectal cancer surgery in an 11-year period median age [20], sex ratio [21], UICC stages [22], surgical techniques [23], rate of emergency surgery [24] and preoperative BMI [25] were similar compared to other studies. Normal weight patients constituted the largest group in this study population. Compared to the weight distribution of the average population underweight, overweight and obese patients were disproportionately represented [12]. Even though BMI is uncomplicated to determine clinically and well comparable to other studies, it is critically discussed in the literature due to its non-uniform use. For example, BMI ≥25 kg/m² was rated overweight or obesity without considering other factors such as muscle mass [26]. Other parameters, such as waist-to-size ratio [15], waist circumference, waist-to-hip ratio or visceral fat are described as being more sensitive [27]. Nevertheless, BMI is the value most frequently used in publications, so that it was also chosen as a reference in the present study.
Of the patients in our study 17% (n=209) presented with preoperative WL, which is comparable to other studies with 7%-28% [28, 29]. Unintentional WL as a dynamic value is dealt with variously by different studies and can be seen as malnutrition. The pathophysiology of unintentional WL is poorly understood. Malignant diseases are cited as the most frequent cause of unintentional WL prior to nonmalignant gastrointestinal diseases, psychiatric conditions and unknown causes [13, 30, 31].
WI rate following colon and rectal resection increased with rising BMI. After colon resection, the WI rate increased significantly in patients with BMI ≥30 kg/m2 as compared to patients with BMI ≤30 kg/m2. Underweight patients did not develop WI following colon resection in either this study or other studies [18].
After rectal resection, obese patients developed significantly more WI than normal weight patients did. This is comparable to other study results [32, 33]. The threshold value for developing WI after rectal resection was seen to be 28.8 kg/m2. There are no comparable threshold values available.
Patients in our study with or without preoperative WL showed no significant difference in WI rate following colon or rectal resection. An increased WI rate caused by WL from malnutrition proved to be an independent risk factor [34]. Furthermore, the possibility of lowering the WI rate for WL by using immunonutrition has already been described [35]. However, another study performed with preoperative immunonutrition therapy showed no change in the postoperative complication rate when bloodwork improved [36]. In contrast to our study, Tang et al. showed an increased WI rate after preoperative WL [37]. Evidence on the influence of preoperative WL on the WI rate following colon and rectal resection is therefore inconsistent.
With regard to AL following colon or rectal resection, no significant differences between the different BMI groups were found in our study. The highest rate of AL was seen in the group of obese patients, but without significant difference. Nevertheless, the evidence is inconsistent. Gessler et al. did not report any significant difference in a retrospective evaluation of 600 patients [7]. In retrospective national analyses Midura et al. demonstrated no significant difference in the AL rate between obese (BMI >30 kg/m2) and non-obese patients in a collective of 13684 patients [8] as well as Bakker et al. in a collective of 15667 patients [38]. In contrast, Qiu et al. conducted a meta-analysis of ten studies with a total of 3660 obese and 10829 non-obese patients, and demonstrated a significantly increased risk of AL in patients who already had a BMI >25 kg/m2 (8% versus 2.2%; p<0.001) [39]. This was also evident in Amri et al. [18]. Geiger et al. pointed a significant difference in the AL rate following colon resection between non-obese (BMI <30 kg/m2) and obese patients (BMI >30 kg/m2) out. That study did not discriminate between colon and rectal carcinoma [41]. The AL rate following rectal resection ranged from 7.6% to 9.5% for the various BMI groups. Benoist et al. as well as Qu et al. in a meta-analysis of 1619 prospectively and 2967 retrospectively evaluated patients identified obesity as a risk factor for AL following rectal resection [6, 42]. As possible reasons difficult operative conditions, technical difficulties due to visceral obesity and unclear anatomical conditions were discussed [6, 33, 42]. Following colon resection there was a significant increase in the AL rate in patients with preoperative WL. This was also demonstrated by Rencuzogullari et al. in patients >65 years after elective resections [43]. After rectal resection, a more likely occurrence of AL was demonstrated in patients with preoperative WL than in those without, however with no significant difference. In contrast, Kang et al. showed a significantly increased AL rate following rectal resection in patients with preoperative WL [44]. Midura et al. also demonstrated a significantly higher rate of AL in patients with compared to patients without WL [8]. Like the influence of BMI on the AL rate, the influence of preoperative WL also needs to be further discussed in different data situations.
Following colon resection, obese patients died significantly more frequently than did overweight patients due to septic multiorgan failure. This was also demonstrated by Amri et al., who, however, did not discriminate between colon and rectal carcinoma [18]. Hu et al. pointed out that at 5.9% underweight patients had a significantly higher 30-day mortality rate than did non-underweight patients [45].
Following rectal resection, no significant difference in mortality rate was demonstrated between the different BMI groups. Here, Hu et al. demonstrated also a higher mortality rate after rectal resection in underweight patients [45]. In our study, however, no underweight patient died after rectal resection. Bakker et al. did not demonstrate a correlation between increased BMI and AL or an associated higher mortality [38].
Following colon resection significantly more patients with preoperative WL died than did patients without preoperative WL. After rectal resection no patient with preoperative WL died. The mortality rate in patients without preoperative WL was also very low, namely 0.9%. Midura et al. were able to demonstrate a significant correlation between preoperative WL and AL. They also demonstrated a correlation between AL and the 30-day mortality rate, which was significantly increased. Thus, it can be concluded that preoperative WL influences the 30-day mortality rate [8]. To further determine the influence of BMI and preoperative WL on the 30-day mortality rate, further studies are needed to clarify the inconsistent data.
Significant differences in IHM following colon and rectal resection between the two groups were not demonstrated in our study. This was supported by regression analysis that revealed Charlson Comorbidity Index, ASA score, UICC stage, age and emergency resection to be significant influencing factors for IHM. Neither preoperative BMI, WL, nor the occurrence of WI or AL showed a significant influence. In other studies, a higher mortality rate following colorectal cancer surgery was pointed out in patients with comorbidities, higher UICC stages, age >65 years and obesity [17, 24, 45]. Regression analysis with reference to postoperative IHM revealed neither increased BMI nor WL as an independent risk factor.
Limitations of the present study include the retrospective study design and the difficult comparability with the data of other studies as a consequence of different BMI and WL definitions. Also, selection and information bias has to be pointed out in the context of retrospective data evaluation. Postoperative complications after colorectal cancer surgery are multifactorial, so that a confounding bias of the individual complications cannot be excluded.
Nevertheless, it must be pointed out that despite retrospective data collection, the complete data sets of an 11-year period could be evaluated. A strict distinction between entities of colon and rectum was performed. This resulted in high case numbers of the two collectives in our study. Both preoperative BMI and WL represent a risk factor of increased morbidity in colorectal cancer surgery in our study.