Regional anaesthesia combined with general anaesthesia has become common in the perioperative management of breast cancer surgery patients. Regional techniques have been recognised to provide excellent post-operative analgesia. It enhances multi-modal analgesia regimes while being opioid sparing, reducing incidence of post-operative nausea and vomiting and allowing earlier mobilisation/discharge and improving treatment success. Therefore identifying the correct regional anaesthetic technique for this group of patients is important in providing optimum peri-operative care.

The ultrasound-guided erector spinae plane (ESP) block has been recently described for the successful management of thoracic neuropathic pain. The erector spinae muscle is formed by the spinalis, longissimus thoracis, and iliocostalis muscles that run vertically in the back. The ESP block is performed by depositing the local anaesthetic in the fascial plane, deep to the erector spinae muscle, at the tip of the transverse process of the vertebra. Indirect access to the paravertebral space is gained providing analgesia without the risk of needle injury to structures in close proximity. Cadaveric studies have shown both ventral and dorsal rami of thoracic spinal nerves are affected when local anaesthetic is injected deep to the erector spinae muscle. The erector spinae muscle extends along the thoracolumbar spine allowing extensive cranio-caudal spread. The ventral ramus (intercostal nerve) is divided into the anterior and lateral branches. Its terminal branches provide the sensory innervation of the entire anterolateral wall. The dorsal ramus is divided into 2 terminal branches and it gives the sensory innervation to the posterior wall. Anterior spread of the local anaesthetic to the paravertebral space through the costotransverse foramina and the intertransverse complex provides both visceral and somatic analgesia.

While recent evidence supports statistically significant reductions in pain and opioid consumption among patients who receive an ESP block compared to systemic analgesia alone, the clinical significance of these differences are questionable the effect of ESP block on the patients' quality of recovery following ambulatory breast cancer surgery remains unclear.

Therefore, our objective is to determine whether or not the addition of an ESP block provides both superior analgesia and quality of recovery in patients undergoing ambulatory breast cancer surgery compared to systemic analgesia alone. We hypothesis that patients who received a preoperative ESP block will afford superior postoperative analgesia and improve the quality of recovery over the first 24 hours following surgery compared to those who receive a sham block for their ambulatory breast cancer surgery.

Inclusion Criteria:

• ASA classification: I-III
• BMI < 35 kg/m2
• Day surgery procedure

Exclusion Criteria:

• Prior ipsilateral breast surgery, excluding lumpectomy
• Pre-existing neurological deficit or peripheral neuropathy involving the ipsilateral chest
• Severe, poorly controlled cardiac conditions, significant arrhythmias, severe valvular heart diseases
• Severe, poorly controlled respiratory conditions (severe COPD, severe interstitial lung disease, severe / poorly controlled asthma)
• Contraindication to regional anaesthesia (e.g. bleeding diathesis, coagulopathy, sepsis, infection at the site of potential needle puncture on the posterior chest)
• Patient refusal
• Chronic pain disorder
• Chronic opioid use (≥30 mg oxycodone / day)
• Contraindication (or allergy) to a component of multi-modal analgesia protocol
• Allergy to amide local anaesthetics used in nerve blocks
• Contraindications to any of the components of the standardized general anaesthesia
• Significant psychiatric disorder that would preclude objective study assessment
• Pregnancy/ women with nursing infants
• Unable to provide informed consent
• Unable to speak and read English

Blinded for patient, assessor, anesthesiologist in the operating room