The erector spinae plane (ESP) block is a widely used regional anesthesia technique for postoperative analgesia in thoracic surgery. The block can be performed in different patient positions, most commonly sitting or lateral decubitus, but the effect of patient position on dermatomal sensory spread and analgesic efficacy has not been clearly established.

This prospective, randomized, single-blind clinical trial aims to compare the effects of ESP block performed in sitting versus lateral decubitus position on dermatomal sensory distribution and postoperative analgesic outcomes in patients undergoing video-assisted thoracic surgery.

Adult patients scheduled for elective video-assisted thoracic surgery will be randomly assigned to receive ultrasound-guided unilateral erector spinae plane block either in the sitting position or in the lateral decubitus position. In both groups, the block will be performed at the same thoracic level using 30 mL of 0.25% bupivacaine under ultrasound guidance.

Dermatomal sensory spread will be assessed 15 minutes after block placement using cold sensation (alcohol-soaked cotton) and pin-prick testing. Postoperative analgesia will be standardized in all patients using patient-controlled analgesia with tramadol. Pain scores and opioid consumption will be recorded during the first 24 postoperative hours.

The primary outcome is the extent of dermatomal sensory spread. Secondary outcomes include postoperative pain scores, time to first rescue analgesic, and total opioid consumption within 24 hours.

Inclusion Criteria:

• Age 18 to 75 years
• ASA physical status II-IV
• Scheduled for elective video-assisted thoracic surgery
• Ability to provide written informed consent

Exclusion Criteria:

• Known allergy to local anesthetics
• Chronic opioid use
• Preexisting chronic pain
• Severe cognitive impairment
• Technical difficulty with positioning
• Emergency surgery
• Refusal to participate