This prospective, randomized, controlled, single-center clinical study aims to evaluate the effectiveness of the Serratus Posterior Superior Intercostal Plane Block (SPSIPB) in perioperative pain management among patients undergoing minimally invasive cardiac surgery (MICS). A total of 50 patients undergoing MICS will be randomized into two groups: one receiving standard analgesia plus ultrasound-guided SPSIPB with 30 mL of 0.25% bupivacaine, and a control group receiving standard analgesia only. The primary outcome is total postoperative opioid consumption within 24 hours. Secondary outcomes include postoperative pain scores, extubation time, block-related complications, and recovery parameters such as early mobilization, oral intake, Modified radiological atelectasis score and Quality of Recovery-15 scores.

Minimally invasive cardiac surgery (MICS) is increasingly performed as an alternative to traditional sternotomy-based procedures, providing benefits such as shorter recovery time, reduced hospital stay, and improved cosmetic outcomes. However, despite smaller incisions, patients frequently experience moderate to severe postoperative pain due to rib, pleural, and intercostal nerve injury. Uncontrolled pain may impair respiratory function, delay mobilization, and increase postoperative complications, including chronic post-thoracotomy pain.

Regional anesthesia techniques play an important role in multimodal analgesia after MICS, but the optimal approach remains uncertain. Thoracic epidural and paravertebral blocks have been widely used but are often limited by safety concerns in anticoagulated patients. Recently, ultrasound-guided interfascial plane blocks have gained attention due to their simplicity and low complication rates. The Serratus Posterior Superior Intercostal Plane Block (SPSIPB), first described in 2023, targets the fascial plane between the serratus posterior superior and intercostal muscles, typically at the second or third intercostal level, and provides broad sensory coverage from C3 to T10 dermatomes. To date, there is no published study investigating its use for pain control in MICS.

This study will be conducted at Ankara Bilkent City Hospital as a prospective, randomized, controlled, single-center clinical trial. A total of 50 patients (25 per group) aged 18-75 years (ASA II-III) scheduled for MICS will be enrolled after obtaining informed consent. Participants will be randomly assigned (1:1) to one of two groups using a computer-based randomization method:

Group SPSIPB (n=25): Standard anesthesia and analgesia + ultrasound-guided SPSIPB with 30 mL of 0.25% bupivacaine (unilateral, on the surgical side).

Group Control (n=25): Standard anesthesia and analgesia only. All patients will receive intravenous tramadol (1 mg/kg) and paracetamol (1 g) at the end of surgery. Postoperative patient-controlled analgesia (PCA) with tramadol (15 mg bolus, 15-min lockout, no basal infusion) will be used in both groups. Rescue morphine (0.05 mg/kg) will be administered when NRS >4. Pain scores (NRS 0-10) will be recorded at 6, 12, and 24 hours postoperatively, both at rest and during deep breathing/coughing.

The primary outcome is total postoperative opioid consumption (morphine equivalent, mg) in the first 24 hours.

Secondary outcomes include intraoperative opioid use, postoperative pain scores, extubation time, block-related complications (e.g., pneumothorax, vascular puncture, hematoma, local anesthetic toxicity), postoperative recovery indicators (first oral intake, mobilization, respiratory function), Modified radiological atelectasis score, Quality of Recovery-15 (QoR-15) scores.

All postoperative assessments will be performed by a blinded senior anesthesia resident unaware of group allocation. Statistical analysis will be conducted using SPSS v26. Continuous variables will be analyzed with the independent t-test or Mann-Whitney U test as appropriate; categorical variables will be evaluated with chi-square or Fisher's exact test. Repeated pain scores will be compared using repeated-measures ANOVA or Friedman test. A p value <0.05 will be considered statistically significant.

The study is expected to start in January 2026. The results may provide new evidence on the effectiveness and safety of SPSIPB for postoperative analgesia in minimally invasive cardiac surgery.

Inclusion Criteria:

• Patients scheduled for elective minimally invasive cardiac surgery (MICS)
• Age between 18 and 75 years
• American Society of Anesthesiologists (ASA) physical status II-III
• Body mass index (BMI) between 18 and 35 kg/m²
• Patients who provide written informed consent for participation

Exclusion Criteria:

• Known allergy or hypersensitivity to local anesthetics
• Coagulopathy or current anticoagulant therapy
• Pregnancy or breastfeeding
• Impaired consciousness or inability to communicate
• Failed or technically inadequate block
• Refusal to undergo the block procedure
• Cognitive or mental disorders preventing valid pain assessment
• Opioid intolerance or contraindication to opioid use
• Development of intraoperative or postoperative complications requiring reoperation, prolonged mechanical ventilation, or intensive care
• Incomplete postoperative data or patient withdrawal from the study

This is a single-center academic study. Individual participant data will not be shared publicly. Aggregate results will be reported in publication.

The anesthesiologist performing the block will be aware of group allocation, while the patients and the anesthesiologist responsible for postoperative data collection will remain blinded to the intervention. Pain assessments and other outcome measurements will be conducted by a blinded senior anesthesia resident who is unaware of which treatment each patient received.