Superficial Serratus Anterior Plane Block for Minimal Invasive Cardiac Surgery: a single-center randomized controlled trial

Introduction: Multimodal pain management with serratus anterior plane block (SAPB) in minimal invasive cardiac surgery (MICS) may potentially reduce pain scores and opioid consumption. However, randomized controlled trials investigating the efficacy of a superficial SAPB are missing. Design: Monocentric, prospective, outcome-assessor blinded randomized-controlled trial performed at the General Hospital Maria Middelares, Ghent, Belgium. Methods: 80 patients scheduled for mitral valve surgery (MVS) via port-access, aortic valve replacement via right anterior thoracotomy (AVR-RAT) and minimal invasive direct coronary artery bypass (MIDCAB) surgery were randomized to a superficial SAPB (42 patients) or to routine analgesia (38 patients). In the SAPB group, a single-shot block was performed with 1.25 mg.kg-1 levobupivacaine 0.25% between the latissimus dorsi and serratus anterior muscle. The primary outcome was static pain intensity measured by Numeric Rating Scale (NRS) 12 hours after extubation. Secondary outcomes were static pain intensity measured by NRS at 2, 4, 6 and 24 hours after extubation, cumulative opioid consumption, incidence of postoperative nausea and vomiting (PONV), time to extubation, ICU and hospital length of stay and the amount of carbon dioxide measured by arterial partial pressure (PaCO2). Results: There was no treatment effect on static pain intensity at 12 hours after extubation (mean difference 0.238 95% CI: -0.70 – 1.19; p = 0.78). There was no treatment effect on static pain intensity on the other predefined timepoints nor on the cumulative opioid consumption during the first 48 postoperative hours (mean difference 0.10 mg 95% CI: -2.65 – 2.83; p = 0.911) nor any of the other secondary outcomes. Looking at each surgical intervention separately, the results show a decrement in static pain intensity (mean difference -1.71 95% CI: -2.94 – -0.40; p = 0.021) for patients undergoing MIDCAB surgery at 6 hours post extubation. Conclusions: In our setup, the effect of a single-shot superficial SAPB could not improve static pain intensity scores at 12 hours after extubation compared to a control group receiving standard intravenous opioid analgesia in a mixed group of minimal invasive cardiac surgical patients. Subsequently, the single-shot superficial SAPB could not reduce the cumulative opioid consumption in the first 48 postoperative hours. However, patients undergoing MIDCAB surgery may potentially benefit from this technique.