This prospective randomized controlled study aims to compare the effects of Serratus Posterior Superior Intercostal Plane (SPSIP) block and Rhomboid Intercostal and Subserratus (RISS) block on postoperative pain, respiratory function, and recovery quality in patients undergoing volume-preserving video-assisted thoracoscopic surgery (VATS). Eighty-four patients will be randomized in a 1:1 ratio to receive either SPSIP block or RISS block. The primary outcome is the incidence of somatic pain at the chest drain insertion site at postoperative 2 hours. Secondary outcomes include pain scores, opioid consumption, quality of recovery, diaphragmatic function, pulmonary function, rescue analgesic requirements, postoperative nausea and vomiting, and block-related complications.

Video-assisted thoracoscopic surgery (VATS) is associated with significant postoperative pain that may impair respiratory function and delay recovery. Regional anesthesia techniques are increasingly used to improve analgesia while minimizing opioid-related adverse effects.

The Serratus Posterior Superior Intercostal Plane (SPSIP) block and the Rhomboid Intercostal and Subserratus (RISS) block are novel ultrasound-guided fascial plane blocks that provide thoracic analgesia through different mechanisms. However, comparative clinical evidence regarding their efficacy in VATS patients remains limited.

This prospective, randomized, controlled study will enroll 84 adult patients scheduled for volume-preserving VATS. Participants will be randomly assigned to receive either SPSIP block or RISS block in a 1:1 ratio (42 patients per group).

The primary endpoint is the incidence of somatic pain at the chest drain insertion site at postoperative 2 hours.

Secondary endpoints include postoperative pain scores at rest and during movement, total intravenous morphine consumption during the first 24 postoperative hours, Quality of Recovery-15 (QoR-15) score at postoperative 24 hours, diaphragmatic excursion measured by ultrasonography, peak expiratory flow measurements, rescue analgesic requirements, time to first rescue analgesia, incidence of postoperative nausea and vomiting, and block-related complications.

The study has been approved by the Bursa Sehir Hospital Clinical Research Ethics Committee and will be conducted in accordance with the Declaration of Helsinki and Good Clinical Practice principles.

Inclusion Criteria:

• Patients scheduled for elective biportal video-assisted thoracoscopic surgery (VATS) with lung parenchyma-preserving thoracic procedures under general anesthesia
• American Society of Anesthesiologists (ASA) physical status I-III
• Age between 18 and 75 years
• Provision of written informed consent

Exclusion Criteria:

• Use of anticoagulant or antiplatelet therapy
• Bleeding diathesis
• Known allergy to local anesthetics
• Infection at the planned block site
• Severe chronic pulmonary disease or advanced respiratory failure (e.g., severe COPD or restrictive lung disease)
• Cognitive impairment preventing reliable NRS assessment
• Pregnancy or lactation
• Chronic opioid use (regular use for ≥3 months)
• Severe hepatic or renal failure
• Refusal to participate
• Technical failure or unsuccessful regional block
• Conversion to open thoracotomy during surgery

Individual participant data (IPD) sharing has not yet been determined. The decision regarding data sharing will be made after study completion and in accordance with institutional policies, ethical considerations, and participant confidentiality requirements.

Participants, outcome assessors, and investigators responsible for postoperative data collection and analysis will remain blinded to group allocation throughout the study period. Block procedures will be performed by an anesthesiologist not involved in postoperative assessments.