Postoperative Pain Management
Under the condition that patients were still not awake after the operation, patients were placed in a lateral position for SAPB. Between the anterior axillary line and posterior axillary line, the serratus anterior and latissimus dorsi muscles overlying the fourth to sixth ribs were easily identified by ultrasound (Navis, Wisonic, Shenzhen, China) with a linear transducer (4-15 Hz, L15-4B). The needle was placed on the fourth or sixth rib, not restricted to the fifth rib in the mid-axillary line, to avoid disturbing the surgical incision. After sterilization of the puncture site, the epidural needle (1.6 mm outer diameter, 80 mm length, Tuoren, China) was introduced in the caudal-cephalad direction using an in-plane approach. When the needle almost reached the surface of the rib, 3 ml of saline was injected to test the location of the needle tip and open the potential interfacial space between the rib and the serratus anterior muscle, and then an epidural catheter (0.5 mm inner diameter, 113 mm length, Tuoren, China) was threaded. Catheters were placed 4.5 cm inside the serratus anterior muscle plane beyond the end of the needle and confirmed with ultrasound guidance. After confirming negative aspiration, a bolus of 20 ml of 0.2% (Group L) or 0.375% (Group H) ropivacaine was administered beneath the serratus anterior muscle. The ultrasound scan confirmed that local anesthetic liquid was distributed adequately into the fascial plane between the serratus anterior muscle and the external intercostal muscle. The catheter was inserted and connected to a pump, in which a background infusion at a rate of 7 ml/h of 0.2% (Group L) or 0.375% (Group H) ropivacaine was used continuously until 48 hours postoperatively. Rescue analgesia with 50 mg tramadol if the VAS score was ≥4. The details have been previously reported elsewhere [5, 6].