Description

This prospective interventional dose-finding study is designed to determine the median effective volume (ED50) of 0.25% bupivacaine for ultrasound-guided serratus posterior superior intercostal plane (SPSIP) block in patients undergoing video-assisted thoracoscopic surgery (VATS).

The up-and-down sequential allocation method described by Dixon and Massey will be used. The initial volume of bupivacaine will be administered to the first patient, and subsequent volumes will be adjusted in 2 mL increments according to the response of the preceding patient. If the block is successful, the volume for the next patient will be decreased by 2 mL. In case of block failure, the volume will be increased by 2 mL.

Block success will be defined as the presence of sensory loss to cold in at least two consecutive dermatomes between T3 and T6, assessed 20-30 minutes after block performance, combined with a cumulative fentanyl requirement of less than 2 µg/kg within the first 60 minutes after induction of general anesthesia. Failure will be defined as absence of adequate sensory blockade or the need for fentanyl ≥2 µg/kg.

The up-and-down sequence will be continued until nine reversal points are obtained. The ED50 will be calculated as the mean of the midpoint doses of all independent success-failure pairs. Secondary outcomes will include postoperative pain scores and opioid consumption.

This study aims to provide clinically relevant data to optimize the volume of local anesthetic for SPSIP block while maintaining effective analgesia and minimizing potential adverse effects.