Correlation between Pain and Anal Defecation Function in Postoperative Patients with Colorectal Cancer and Related Factors Affecting Patients' Prognosis

Background: The degree of postoperative pain and defecation function in colorectal cancer will affect patients' prognosis. Therefore, exploring the correlation between postoperative pain and defecation function, and analyzing the related factors, will help to improve the quality of patients' prognosis.  Methods: A total of 94 patients with colorectal cancer admitted to our hospital from March 2022 to June 2023 were retrospectively selected for study. The visual analog scale (VAS) was used to evaluate the pain level of the patients. The low anterior resection syndrome (LARS) scale was used to evaluate bowel function of the patients, and the incidence of LARS was recorded. The patients were grouped according to whether or not they had the complications of LARS, and they were divided into the groups of concurrent LARS and non-concurrent LARS. The patients' anorectal pressure was measured, and the measurements included maximum tolerated volume (MTV), anorectal resting pressure (ARP), and maximum squeeze pressure (MSP). Pearson's correlation coefficient was used to test associations between anal defecation function and postoperative pain and anorectal manometry. Logistic regression was used to test predictors of concurrent LARS, and the value of each of the indices for prediction of LARS was examined using the receiver operating characteristic (ROC).  Results: Patients' VAS scores were positively correlated with LARS scores (p < 0.05). A total of 22 patients with VAS score ≥20 points were found to have a LARS incidence of 23.40% based on the LARS score. The VAS score was higher in the concurrent LARS group than in the non-concurrent LARS group (p < 0.05). The concurrent LARS group had a higher percentage of patients with age ≥60 years, body mass index ≥24 kg/m2, anastomotic position <5 cm from the anal verge, preoperative radiotherapy, and anastomotic fistula than the non-current LARS group (p < 0.05). The levels of MTV, ARP, and MSP were lower in patients in the concurrent LARS group than in the non-current LARS group (p < 0.05). Patients' LARS scores were negatively correlated with MTV (r = –0.420), ARP (r = –0.300) and MSP (r = –0.220) levels (p < 0.05). Logistic regression analysis showed that anastomotic position <5 cm from the anal verge, preoperative radiotherapy, anastomotic fistula, high VAS level, and low MTV level were all significant predictors of concurrent LARS. Anastomotic position, whether or not radiotherapy was administered preoperatively, anastomotic fistula, VAS score, and MSP level all had high sensitivity and specificity for prediction of concurrent LARS, and the combined area under the curve (AUC) of each index was 0.921, sensitivity was 0.818, and specificity was 0.944.  Conclusion: LARS is strongly associated with the patient's pain level, and factors such as anastomotic position <5 cm from the anal verge, preoperative radiotherapy, anastomotic fistula, high VAS level, and low MTV level will increase the risk of concurrent LARS in patients.