Erector Spinae Plane Block Versus Paravertebral Block in Patients Undergoing Elective Breast Surgery. A Randomized Controlled Trial Comparing Dermatomal Spread.

Paravertebral block (PVB) has been shown to provide excellent analgesia for major breast surgery. Advantages of a PVB technique include reduced postoperative pain, analgesic consumption, opioid-related side effects, and shorter post anesthesia care unit (PACU) stay. There is also evidence to suggest that PVB may have a favorable impact on cancer recurrence after mastectomy. Paravertebral blockade results in somatosensory and sympathetic blockade after injection of local anesthetic solution to the paravertebral space posterior to the pleura. Erector spinae plane (ESP) block is a recently described technique which may be an alternative to PVB for providing thoracic analgesia. Numerous case reports and case series describe ESP block for the management of acute and chronic thoracic pain. It involves injection of local anesthetic into the fascial plane deep to erector spinae muscle. Radiological imaging in a cadaver model has demonstrated that a single injection at the level of the T5 transverse process produced cranio-caudal spread between C7 and T8. This accounts for the extensive sensory block that has been observed in case reports and is at least as extensive as the spread seen with PVB.

ESP is a more superficial block with a better defined end-point - injection between the bony transverse process and erector spinae muscle. A more superficial ultrasound-guided block will be faster to perform and less painful for the patient. Furthermore, ESP does not have the same risk of pneumothorax as PVB.There have been no randomized controlled trials involving ESP to date. All descriptions of the technique have been in case report / series format.

The investigators hypothesize that ESP block efficacy is not inferior to PVB with reference to dermatomal sensory spread and analgesic efficacy, while being easier to perform, has less associated discomfort and fewer complication risks.

All eligible participants will be randomized to the PVB arm or the ESP arm after fully informed consent has been obtained. Subjects randomized to the PVB arm will have an ultrasound-guided paravertebral block performed pre-operatively in the anesthesia block room with 20ml of a ropivacaine / bupivacaine mixture. Subjects randomized to the ESP arm will have an ultrasound-guided erector spinae plane block performed pre-operatively in the anesthesia block room with 20ml of a ropivacaine / bupivacaine mixture. Conduct of intra-operative anesthesia will be at the discretion of the attending anesthesiologist.

The primary outcome is equivalent dermatomal spread for ultrasound-guided single-injection ESP block performed at T4-T5 level and ultrasound-guided single-injection PVB block at the same level.