The erector spinae plane block (ESPB) is a less invasive, safer, and technically easy alternative procedure to conventional neuraxial anesthetic techniques. In contrast to common neuraxial techniques such as paravertebral and epidural injections, the ESPB targets an interfascial plane which is far from the spinal cord, root, and pleura. First applied to thoracic neuropathic pain, currently ESPB is being applied to postoperative pain control and includes variable clinical situations. In the abdomen and thoracic wall, thoracic ESPB can be applied for pain control after cardiac surgery, video-assisted thoracic surgery, laparoscopic cholecystectomy, and thoracotomy. Recently, favorable postoperative pain control after lumbar spinal or lower limb surgeries has been reported with lumbar ESPB. In addition, ESPB has also been used for chronic pain conditions in the upper and lower extremities. The perfusion index (PI) is a numerical value for the ratio between pulsatile and non-pulsatile blood flow measured by a special pulse oximeter. Although the special probe for PI measurement is relatively more expensive compared with ordinary pulse oximetery probes, its benefit as a marker of peripheral perfusion and as an idex for sympathetic stimulation have increased its use progressively.~ESPB can achieve analgesic effect by blocking the ventral and doramal ramus and possibly by diffusion into paravertebral space. In constrast to lumar region, thoracic paravertebral space is very close to the sympathetic chain. Therefore, sympatholytic effect might be achieved by thoracic ESPB. No previous study has demonstrated the sympatholytic effect of ESPB.
The primary endpoint of this study was to identify if erector spinae plane bloock (ESPB) demonstrates any sympatholytic effect.~The secondary endpoint of this study was to compare the sympatholytic effect of ESPB bewteen 10 ml and 20 ml ESPBs.