Is Serratus Anterior Plane Block (SAPB) With Adjuvant Medications Better at Managing Post-operative Pain Than Serratus Anterior Plane Block With Bupivacaine Alone in Patients Undergoing Video-assisted Thoracoscopy?

Many thoracic surgeons have switched from open thoracotomy to video-assisted thoracoscopy (VATS), when possible, in efforts to decrease length of hospital stays, decrease analgesic requirements, and decrease postoperative pain.

The serratus anterior plane block (SAPB) has been used effectively for the management of pain in the context of rib fractures, rib contusions, thoracoscopic surgery, thoracotomy, breast surgery, and post-mastectomy pain syndrome. It has been shown to have similar efficacy to thoracic epidurals in open thoracotomy.

The serratus anterior muscle originates from the anterior aspect of ribs 1 through 7-10 and inserts on the medial border of the scapula. It consists of 7 to 10 serrated tendinous projections that originate on each rib and is innervated by the long thoracic nerve. Deep and superficial potential spaces bound the serratus anterior. At the level of the fifth rib, the superficial plane forms from the anterior aspect of the serratus anterior and the posterior aspect of the latissimus dorsi muscle. The deep plane forms from the posterior aspect of the serratus anterior and the external intercostal muscles and ribs. Injecting in either plane will achieve analgesia to the anterolateral chest wall with reportedly similar efficacy and an equivalent area of cutaneous sensory loss.

The SAPB targets the lateral cutaneous branches of the thoracic intercostal nerves, which arise from the anterior rami of the thoracic spinal nerves and run in a neurovascular bundle immediately inferior to each rib. At the midaxillary line, the lateral cutaneous branches of the thoracic intercostal nerve traverse through the internal intercostal, external intercostal, and serratus anterior muscles innervating the musculature of the lateral thorax. These branches of the intercostal nerves, therefore, travel through the two potential spaces described above. Local anesthetic inserted into these planes will spread throughout the lateral chest wall, resulting in paresthesia of the T2 through T9 dermatomes of the anterolateral thorax.

Rebound pain is possible after serratus anterior block because analgesia provided by bupivacaine typically lasts around six hours. Local anesthetic systemic toxicity is a potential complication of regional anesthesia as well. For this reason, dilute anesthetic is used, and a maximum dose of 2 mg/kg of bupivacaine is the recommendation. Pneumothorax is a potential complication but would entail catastrophic error because the fascial planes targeted in this block are superficial to the ribs, and the pleural line can be visualized clearly on ultrasound. If a pneumothorax is suspected, ultrasound can help to confirm lung sliding immediately after the procedure. Nerve injury is unlikely given the needle is not steered directly at nerves, but instead towards the plane through which the nerves run.