Ultrasound-guided Thoracic Paravertebral Block Versus Ultrasound-guided Thoracic Erector Spinae Plane Block for Pain Management After Unilateral Total Mastectomy: a Randomized Controlled Trial

Despite substantial advances in our understanding of the pathophysiology of pain and availability of newer analgesic techniques postoperative pain is not always effectively treated. Optimal pain management technique balances pain relief with concerns about safety and adverse effects associated with analgesic techniques. Currently, postoperative pain is commonly treated with systemic opioids, which are associated with numerous adverse effects including nausea and vomiting, dizziness, drowsiness, pruritus, urinary retention, and respiratory depression. Use of regional and local anesthesia has been shown to reduce opioid requirements and opioid-related side effects. Therefore, their use has been emphasized. The advent of ultrasound guided regional anesthesia has brought more precision to these techniques, including the ability to visualize the anatomy, perform real-time navigation, and direct observation of local anesthetic spread, as it allows a greater degree of sensory and motor blockade. Thoracic paravertebral block (TPVB) has been used for analgesia of the thoracic wall since it was first described in 1905. A relatively recent alternative to the TPVB is the thoracic erector spinae plane (TESP) block, which involves the ultrasound-guided injection of local anesthetic into the interfascial plane deep to the erector spinae muscle at the level of the transverse process. It results in a loss of somatic sensory sensation across multiple unilateral dermatomes due to local anesthetic mediated blockade of the dorsal and ventral rami of the spinal nerve roots. It is increasingly being used due to ease of placing the block and a perception of greater safety. It has been shown to provide pain relief from rib fractures, thoracotomy, and chronic neuropathic pain of the chest wall. However, to date, TESP block has not been compared with TPVB in regards to analgesia with mastectomy surgery, which has been extensively studied.

The investigators hypothesize that TESP block will provide similar (i.e., non-inferior) analgesia compared to TPVB block while reducing the cumulative consumption of oral morphine equivalents during the 24h post-operative period. The two co-primary aims of the study are to compare a) pain scores at 2h post-operative period, and b) cumulative consumption of oral morphine equivalents during the 24h post-operative period. Secondary objectives include comparison between the group in terms of pain scores at 6, 12, 24, and 48 hours post-operatively, as well as block-related morbidity (e.g.- pneumothorax), time to perform each block, and opioid-related adverse effects (e.g.- postoperative nausea and vomiting).