From January 2003 through December 2013, a total of 392 patients underwent radical surgery for rectal adenocarcinoma in our hospital. We excluded 131 patients who underwent emergency surgery or laparoscopic surgery and studied the remaining 260 patients. Data on these patients were retrospectively collected to estimate the incidences of complications within 30 days after surgery and to compare the value of each risk score for predicting the probability of complications.
Risk evaluation scores
We studied the following risk evaluation scores: Estimation of Physiologic Ability and Surgical Stress Comprehensive Risk Score (E-PASS CRS) [12], Surgical Apgar Score (SAS) [13], Prognostic Nutritional Index (PNI) [14], Colorectal POSSUM (CR-POSSUM) [16], and Neutrophil-to-lymphocyte Ratio (NLR) [15]. The preoperative general condition, concomitant diseases, and complications of each patient were examined from their medical records. Surgical information, such as intraoperative vital signs and bleeding volume, was obtained from each patient’s surgical and anesthesiologic records.
E-PASS CRS was calculated as described by Haga et al. [12]. The preoperative risk score, reflecting the patient’s physiological status before surgery, the surgical stress score, reflecting the degree of surgical invasion, and the comprehensive risk score, representing the overall risk associated with preoperative risk and surgical stress, were calculated for each patient. SAS was calculated from the intraoperative bleeding volume, the minimal heart rate, and the minimal mean blood pressure, as described by Gawande et al. [13]. PNI was calculated by the following formula, proposed by Onodera et al. [14]: PNI = 10 × serum albumin level (g/dL) + 0.05 × total lymphocyte count (mm3). CR-POSSUM was calculated as reported by Tekkis et al. [16, 17] on the basis of the Physiological Score (PS), derived from age and the results of preoperative assessments of cardiac dysfunction, systolic blood pressure, heart rate, serum hemoglobin concentration, and urea nitrogen concentration, and the Operative Severity Score (OS), derived from surgical invasion, Duke’s classification, and intraoperative findings. The CR-POSSUM score was the sum of PS and OS. NLR was calculated using blood samples obtained at initial presentation. In patients who received preoperative chemoradiotherapy, the score was calculated before chemoradiotherapy.
Classification and severity of complications
We studied the following 4 types of complications occurring within 30 days after surgery: all complications, infectious complications (wound infection, inflammation of the pelvic dead space, and intraabdominal abscess), anastomotic leakage, and intestinal obstruction. All complications included exacerbation of underlying disease. The diagnosis of anastomotic leakage was based on the properties of drainage fluid or radiographic findings. The severity of complications was evaluated according to the Clavien-Dindo classification [18]. All complications, infectious complications, and intestinal obstruction of Clavien-Dindo grade 3a or higher that required surgical intervention and anastomotic leakage of Clavien-Dindo grade 3b or higher that required reoperation were defined as complications.
Evaluation of risk factors for anastomotic leakage
To investigate the risk factors for anastomotic leakage, we excluded 76 patients with a diverting stoma at initial surgery from the 187 patients who underwent low anterior resection and studied the remaining 111 patients. To compare the accuracy of each score for predicting the risk of anastomotic leakage, we calculated the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy rate for each score. We then compared the values among the different scores. A multivariate analysis was then performed to identify risk factors for anastomotic leakage in patients without a diverting stoma at initial surgery. The model included factors that were significantly related to anastomotic leakage in our study, as well as sex, body-mass index (BMI), smoking history, the American Society of Anesthesiologists (ASA) classification, tumor location, and preoperative chemoradiotherapy, ypStage, which have been reported to be risk factors for anastomotic leakage in patients with rectal cancer [19, 20].
Statistical analysis
The cutoff value (COV) for each score was calculated by risk evaluation analysis, performed using receiver operating characteristic curves (ROC) in which the presence of complications was considered a positive result. The patients were divided into 2 groups according to whether their score was less than the COV or equal to or greater than the COV, and the incidence of complications was compared. For risk evaluation analysis, the COV of the PNI was set at 40, as recommended by Onodera et al. [14]. The 2 groups were compared with the use of the Chi square test. Multiple logistic regression analysis was performed. P values of less than 0.05 were considered to indicate statistical significance. All statistical analyses were performed with the use of JMP® 10 software (SAS Institute Inc., Cary, NC, USA).
This study was approved by the institutional review board of Tokai University (15R-217).