Effect of ultrasound - guided erector spinae plane block VS paravertebral nerve block for intraoperative and postoperative analgesia for radical surgery of colorectal cancer: a randomized, controlled clinical study

Interventions: Ultrasound-guided erector spine block group (E):Before the induction of anesthesia, 30ml of 0.35% ropivacaine was injected into the erector spinae plane at L4 level on both sides under ultrasound guidance.;Ultrasound-guided paravertebral nerve block (P):Before the induction of anesthesia, 30ml of 0.35% ropivacaine was injected into the paravertebral space at L4 level on both sides under ultrasound guidance.
Primary outcome(s): dose of opioids in surgery;VAS scores for rest and exercise
Study Design: Randomized parallel controlled trial