SPIP vs ESP Block in Cardiac Surgery

This multicenter, parallel-group, randomized controlled non-inferiority trial will compare bilateral SPIP block with bilateral ESP block for postoperative analgesia in adults undergoing first-time on-pump cardiac surgery through median sternotomy.

Patients aged 18-80 years will be enrolled across tertiary cardiac surgery centres in Türkiye and randomly assigned in a 1:1 ratio, stratified by center, to receive either bilateral SPIP block or bilateral ESP block. Both interventions will be performed before induction of general anesthesia. Participants in the SPIP group will receive ultrasound-guided injection between 4th and 5th ribs, whereas participants in the ESP group will receive bilateral ultrasound-guided injection at the T5 transverse process.

Perioperative anesthesia, postoperative multimodal analgesia, and patient-controlled morphine analgesia will be standardised across participating centers. Postoperative outcome assessors will remain blinded to treatment allocation. Block success will be assessed using cold sensation testing before induction.

The primary outcome is cumulative opioid consumption from extubation to 24 hours after extubation, expressed as intravenous morphine milligram equivalents (IV-MME). The primary objective is to determine whether SPIP block is non-inferior to ESP block using a prespecified non-inferiority margin of 3 mg IV-MME. Secondary outcomes include time-weighted average pain intensity at rest and during coughing over the first 24 hours after extubation, Quality of Recovery-15 scores at 24 hours and hospital discharge, and the incidence of chronic postsurgical pain at 3 months. Exploratory outcomes include rescue analgesic requirements, postoperative nausea and vomiting and other opioid-related adverse effects, time to extubation, intensive care unit and hospital length of stay, block failure, and block-related complications.

The primary non-inferiority analysis will be performed in both the intention-to-treat and per-protocol populations. The between-group location shift in 24-hour IV-MME consumption will be estimated using the Hodges-Lehmann method with a two-sided 95% confidence interval. Non-inferiority will be concluded if the upper bound of the confidence interval for the SPIP minus ESP difference is less than 3 mg IV-MME.

Inclusion criteria

• written informed consent
• age 18 to 80 years
• American Society of Anesthesiologists (ASA) physical status II-IV
• Scheduled for first-time on-pump cardiac surgery through a median sternotomy, including coronary artery bypass grafting, valve repair or replacement, or another open cardiac procedure requiring sternotomy
• Ability to understand postoperative pain and recovery assessments and to use an intravenous patient-controlled analgesia device.

Exclusion criteria

• Emergency surgery.
• Previous median sternotomy.
• Minimally invasive cardiac surgery without median sternotomy.
• Known allergy or hypersensitivity to bupivacaine, morphine, paracetamol, ondansetron or another protocol medication.
• Chronic opioid use, defined as continuous opioid treatment for at least 30 days at a daily oral morphine equivalent dose of 15 mg or more.
• Alcohol or substance use disorder that, in the investigator's judgment, may affect adherence or outcome assessment.
• Clinically significant hepatic dysfunction, defined as alanine aminotransferase or aspartate aminotransferase greater than twice the upper limit of normal.
• Clinically significant renal dysfunction, defined as serum creatinine greater than twice the upper limit of normal.
• Coagulation disorder or antithrombotic treatment that precludes safe block performance according to current institutional guidance.
• Infection at a planned needle insertion site.
• Severe psychiatric illness, cognitive impairment or communication difficulty preventing valid postoperative assessment.
• Pregnancy or breastfeeding.
• Body mass index greater than 40 kg/m².
• Prolonged postoperative mechanical ventilation, defined as failure to achieve extubation within 8 hours after surgery.
• Refusal to participate.