Abstract: Objective To compare the analgesic effects of different approaches of quadratus lumbar muscle block (QLB) on patients undergoing laparoscopic radical resection of rectal cancer. 
Methods A total of 128 patients with rectal cancer who received laparoscopic radical resection of rectal cancer in our hospital were selected and divided into anterior approach group (injection of fascia plane between QLB psoas muscle and psoas major muscle, n=32), lateral approach group (external injection of QLB, n=32), posterior approach group (posterior injection of QLB, n=32) and control group ［routine patient-controlled intravenous analgesia (PCIA), n=32］. The first compression time of PCIA, the time of first exhaust and the first time of off-bed activity were compared among the four groups. The visual analog scale (VAS)  scores were compared in the four groups at different time points after operation. The effective number of PCIA compression and the total amount of sufentanil within 24 h after surgery were compared among the four groups. The adverse reactions of the four groups were compared. 
Results The first compression time of PCIA in the anterior approach, lateral approach, and posterior approach groups was longer than that of the control group (P＜0.05), and the first exhaust time and the first time of off-bed activity were shorter than those of the control group (P＜0.05). The differences in VAS scores in interaction between groups, time points and time points between groups were statistically significant (P＜0.05). The effective number of PCIA compression and the total amount of sufentanil within 24 h after surgery in the anterior approach, lateral approach and posterior approach groups were lower than those in the control group (P＜0.05), and lower in the anterior approach group than in the lateral approach group and the posterior approach group (P＜0.05). The total incidence of adverse reactions in the anterior approach, lateral approach and posterior approach groups was lower than that in the control group (P＜0.05). 
Conclusion Different approaches of QLB guided by ultrasound can promote postoperative recovery of patients, improve the analgesic effect of patients after laparoscopicradical resection of rectal cancer, and reduce the dosage of opioids and the incidence of adverse reactions. However, QLB via anterior approach is superior to that via lateral approach and posterior approach in terms of analgesia and reduction of the amount of postoperative analgesics.

Key words: rectal neoplasms, laparoscopes, ultrasonography, analgesia