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].