The primary endpoint of this study is to compare the pain relief and peripheral perfusion index using different volume of local anesthetics in erector spinae plane block.

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. To investigate the possible mechanism of action of the ESPB, many previous studies have focused on examining the physical spread of the injected agent. Commonly, contrast dye injections in human cadavers have been utilized to assess the spread level. Physical spread level was determined using various methods including direct dissection or sectioning, computed tomography (CT), thoracoscopic inspection, or magnetic resonance imaging (MRI) with radiocontrast injection. Apart from human cadaver studies, physical spread level has been evaluated in alive patients using a variable volume of local anesthetics mixed with radiocontrast. Perfusion index is an indirect method which can present the degree of peripheral perfusion. Moreover, it is known as a more sensitive measurement tool than the rise of skin temperature. The apply of perfusion index is very simple and noninvasive. The degree of PI increase has been used to determine the success of peripheral nerve block. The volume of local anesthetics has been used 10-30 ml. However, most effective dosage with proper pain relief has never been suggested.

Inclusion Criteria:

• lumbar disc herniation
• lumbar foraminal stenosis
• lumbar central stenosis
• lumbar spondylolisthesis
• numerical rating scale > 4
• back pain functional scale < 45
• duration of pain > 1 mon
• patients who can fully understand all items described in back pain functional scale

Exclusion Criteria:

• Allergy to local anesthetics or contrast medium
• Pregnancy
• Spine deformity
• Prior history of lumbar spine surgery
• No previous lumbar MRI or CT
• Patients with coagulation abnormality