Minimum Effective Volume of Bupivacaine for Serratus Posterior Superior Intercostal Plane Block in Video-Assisted Thoracoscopic Surgery

Determination of the Median Effective Volume (ED50) of Bupivacaine for Serratus Posterior Superior Intercostal Plane Block in Patients Undergoing Video-Assisted Thoracoscopic Surgery Using the Dixon Up-and-Down Method

This study aims to determine the minimum effective volume of bupivacaine required for the serratus posterior superior intercostal plane (SPSIP) block in patients undergoing video-assisted thoracoscopic surgery (VATS). The SPSIP block is an ultrasound-guided regional anesthesia technique used to provide postoperative pain relief after thoracic surgery.

Using a stepwise dose-adjustment method, the volume of local anesthetic will be increased or decreased based on the effectiveness of the block in each patient. The main outcome of the study is to identify the volume that provides effective pain control in 50% of patients. The results may help optimize pain management while minimizing drug exposure.

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.

Inclusion Criteria:

• Age 18 years or older
• Scheduled for elective video-assisted thoracoscopic surgery (VATS)
• American Society of Anesthesiologists (ASA) physical status I-III
• Planned to receive ultrasound-guided serratus posterior superior intercostal plane block for postoperative analgesia
• Ability to provide written informed consent

Exclusion Criteria:

• Refusal to participate in the study
• Known allergy or contraindication to local anesthetics
• Infection at the block injection site
• Coagulation disorders or anticoagulant therapy contraindicating regional anesthesia
• Severe respiratory insufficiency
• Chronic opioid use or chronic pain syndrome
• Pregnancy
• Inability to cooperate or communicate postoperative pain scores