This single-centre randomized clinical trial will compare two regional anaesthesia techniques for postoperative pain control in adult patients undergoing elective coronary artery bypass grafting (CABG) with sternotomy. All patients will receive a bilateral parasternal block as part of routine multimodal analgesia. Patients will be randomized to receive either parasternal block alone or a combination of parasternal block and serratus anterior plane block. The primary objective is to evaluate whether adding a serratus anterior plane block improves postoperative pain scores compared with parasternal block alone. Secondary objectives include comparing opioid consumption, need for rescue analgesics, opioid-related side effects, and length of stay in the intensive care unit and hospital.

Background: Postoperative pain after coronary artery bypass surgery arises from both the sternotomy incision and the chest tube insertion sites and may impair mobilisation, deep breathing, and coughing. Fascial plane blocks of the chest wall, such as parasternal block and serratus anterior plane block, are increasingly used because they are technically simple and have a low complication risk. Previous observational data suggested that combining bilateral parasternal block and serratus anterior plane block provides effective analgesia after CABG, but sample size was small and no randomized comparison has been performed.

Objectives: The primary objective is to compare postoperative pain intensity between parasternal block alone and parasternal plus serratus anterior plane block in adult patients undergoing elective CABG with sternotomy. Secondary objectives are to compare total opioid consumption (tramadol via patient-controlled analgesia), need for rescue analgesics, incidence of opioid-related adverse events (e.g. nausea and vomiting), and intensive care unit and hospital length of stay between the two groups.

Methods: This is a prospective, randomized, parallel-group, low-risk interventional study conducted in the Anaesthesiology and Reanimation Department of Ankara Etlik City Hospital. Adult patients (≥18 years) scheduled for elective coronary bypass surgery due to coronary artery disease and classified as ASA II-IV will be screened for eligibility. After induction of general anaesthesia and before surgical incision, all patients will receive an ultrasound-guided bilateral parasternal block. Patients randomized to the experimental arm will additionally receive a bilateral serratus anterior plane block. Local anaesthetic dosing will follow routine clinical practice, with a total dose not exceeding 2 mg/kg of 0.25% bupivacaine. All patients will receive 40 ml of 0.25% bupivacaine. The parasternal group will receive a bilateral parasternal block via administering 20 ml of 0.25% bupivacaine bilaterally. The parasternal+serratus anterior plane block group will receive 10 ml of 0.25% bupivacaine to bilateral parasternal and deep serratus planes.

Pain intensity will be assessed using the Numeric Rating Scale (NRS, 0-10) at extubation (T0) and postoperative 4, 6, 12, and 24 hours (T4, T6, T12, T24). Postoperative analgesia will include standard intravenous acetaminophen and tramadol via patient-controlled analgesia; total tramadol dose (demand and delivered), rescue analgesic requirement, and adverse events will be recorded in the first 24 postoperative hours.

Sample size: Based on a two-group comparison with an effect size of 0.6, α = 0.0,5, and β = 0.2, 72 patients are required to achieve 80% power.

Inclusion Criteria

• Age ≥ 18 years
• American Society of Anesthesiologists (ASA) physical status III-IV
• Scheduled for elective coronary artery bypass grafting surgery with sternotomy for coronary artery disease
• Able to provide written informed consent

Exclusion Criteria

• Allergy or contraindication to local anaesthetic agents
• Minimally invasive bypass surgery or off-pump procedures planned
• Emergency cardiac surgery
• Preoperative Numeric Rating Scale (NRS) pain score ≥ 3
• Chronic opioid use in the preoperative period
• Infection or structural abnormality at planned block sites
• Any condition preventing postoperative pain assessment or PCA use (e.g. severe cognitive impairment)

De-identified individual participant data underlying the primary publication may be shared upon reasonable request to the principal investigator after publication of the results.

De-identified individual participant data underlying the primary publication may be shared upon reasonable request to the principal investigator after publication of the results.

De-identified individual participant data underlying the primary publication may be shared upon reasonable request to the principal investigator after publication of the results.