Dual Plane Block May Cut Opioid Use After Bypass Surgery

Coronary artery bypass grafting (CABG) is a common cardiac surgical procedure, frequently associated with significant postoperative pain. This pain, often managed with systemic opioids, can lead to complications such as respiratory depression, ileus, and prolonged hospital stays.¹ The drive to reduce opioid exposure has led to increased interest in regional anesthetic techniques.² Thoracic wall blocks, specifically the pectoral nerve (PECS) block and the serratus anterior plane (SAP) block, have shown efficacy in managing pain from thoracic procedures by targeting the intercostal nerves.³ Annually, hundreds of thousands of CABG procedures are performed worldwide, making effective and safe pain management a critical component of patient recovery and hospital resource utilization. The sternotomy incision, a standard approach for CABG, transects multiple layers of muscle and bone, leading to somatic pain that is often severe in the immediate postoperative period. Visceral pain components also contribute to the overall pain experience, though regional blocks primarily target somatic pain pathways.

What the study did

A prospective, randomised controlled trial investigated the efficacy of a dual plane block, comprising both PECS I and SAP blocks, in patients undergoing elective CABG via sternotomy.⁴ The trial enrolled 120 adult patients (N=120) scheduled for isolated CABG. Patients were randomly assigned to receive either the dual plane block in addition to standard analgesia (intervention group, n=60) or standard analgesia alone (control group, n=60). The dual plane block was performed bilaterally under ultrasound guidance after induction of general anesthesia but prior to surgical incision.⁴ Patient inclusion criteria typically involved adults aged 18-75 years undergoing primary, elective CABG, with an American Society of Anesthesiologists (ASA) physical status classification of II or III. Exclusion criteria often included emergency surgery, reoperation, known allergy to local anesthetics, significant coagulopathy, or pre-existing chronic pain requiring opioid therapy. This careful selection aimed to ensure a homogenous study population and minimize confounding factors.

The PECS I block involved injecting 10 mL of 0.25% bupivacaine between the pectoralis major and pectoralis minor muscles. The SAP block involved injecting 20 mL of 0.25% bupivacaine into the plane superficial to the serratus anterior muscle, typically at the mid-axillary line between the 4th and 5th ribs.⁴ Standard analgesia in both groups included intravenous paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs) where not contraindicated, along with patient-controlled analgesia (PCA) with morphine.⁴ The rationale for combining PECS I and SAP blocks is to provide more comprehensive coverage of the anterior and lateral thoracic wall, targeting the lateral and anterior cutaneous branches of the intercostal nerves (T2-T6) that innervate the sternum and surrounding chest wall. The PECS I block specifically targets the lateral pectoral nerve and medial pectoral nerve, while the SAP block targets the lateral cutaneous branches of the intercostal nerves.

Key Findings

The primary outcome was total opioid consumption, measured as intravenous morphine equivalents, during the first 48 hours post-surgery. Secondary outcomes included pain scores at rest and with movement, time to first rescue analgesia, incidence of postoperative nausea and vomiting (PONV), and length of hospital stay.⁴

Patients in the dual plane block group demonstrated a statistically significant reduction in total 48-hour postoperative opioid consumption. The mean morphine equivalent consumption was 28.5 mg (SD 7.2) in the intervention group compared to 45.1 mg (SD 8.9) in the control group (p < 0.001).⁴

Pain scores, assessed using a Visual Analogue Scale (VAS), were also lower in the dual plane block group at multiple time points. At 6, 12, and 24 hours post-extubation, mean VAS scores at rest were significantly lower in the intervention group (e.g., 6 hours: 3.2 vs 5.8, p < 0.001). Similarly, pain scores with movement were reduced.⁴ The time to first rescue analgesia was significantly prolonged in the dual plane block group, with a mean of 8.7 hours (SD 1.5) versus 4.1 hours (SD 0.9) in the control group (p < 0.001).⁴

The incidence of PONV was also lower in the intervention group (15% vs 35%, p = 0.012), likely attributable to reduced opioid exposure. There was no significant difference in the length of hospital stay between the two groups. No major complications related to the block procedure, such as pneumothorax or local anesthetic systemic toxicity, were reported.⁴

Limitations and Next Steps

The study was conducted at a single centre, which may limit the generalisability of the findings. The relatively small sample size (N=120) also warrants caution. Future multicentre trials with larger cohorts are needed to confirm these results and to evaluate the long-term impact on chronic post-surgical pain and opioid dependence. Further research could also explore the optimal local anesthetic concentration and volume, as well as the duration of catheter placement for continuous blocks.⁴ The lack of blinding for outcome assessors, while challenging in regional anesthesia studies, represents a potential source of bias. While the primary outcome of opioid consumption is objective, pain scores are subjective and could be influenced. Investigating the cost-effectiveness of implementing this dual plane block into routine clinical practice is also a crucial next step, considering the resources required for ultrasound equipment and trained personnel. The study's focus on isolated CABG means its applicability to other cardiac procedures or combined surgeries remains to be determined.