Group ES
In a prone position, the TP of the 6th thoracic vertebra was identified using ultrasound with downward counting from the 1st rib. Following standard skin disinfection, a linear transducer (6-13 MHz HFL38x; Fujifilm SonoSite, Bothell, WA) was placed parallel to the thoracic spine to visualize the 6th TP, and an 18G Tuohy needle was inserted by the in-plane technique, in a caudad to cephalad direction. After the needle tip touched the 6th TP, 10 mL of normal saline was applied to confirm spreading to the deep part of the erector spinae muscle and to make space for catheter insertion. Then, a multi-orifice catheter was implanted 3 cm beyond the needle tip. The anesthesiologist checked the location of the catheter tip by fluoroscopy. A loading dose of 20 mL 0.375% ropivacaine was injected 30 minutes before the end of surgery. A programmed intermittent bolus infusion (PIBI) of 15 mL 0.2% ropivacaine every 3 h was started 3 h after injecting the loading dose (20 mL) using a PCA pump with a 5 mL bolus and a lock-out interval of 20 minutes for 2 postoperative days.