Pain following mastectomy surgery for breast cancer can be significant. Poorly managed pain in the immediate time-period following surgery can potentially lead to long-term (chronic) pain conditions. There is still a need to find the safest, least invasive, and most effective method to manage this pain. The investigators believe that a new technique of injecting local anesthesia (freezing) in to specific areas at the end of mastectomy surgery may be a very important step to managing pain after breast surgery. The investigators would like to begin by performing a pilot study, meaning the investigators will perform the technique in patients and compare what their pain outcomes are to patients who have not had the technique.

Mastectomy is associated with significant acute postoperative pain. It has been shown that inadequately managed post-mastectomy pain in breast cancer patients can have detrimental physiological, psycho-behavioural, recovery and healthcare utilization consequences. Most significantly, acute postoperative pain appears to be a substantial risk factor for progression to chronic post-surgical pain (CPSP), occurring in up to 68% of patients,, with higher severity of acute pain being linked with a greater progression to CPSP. A multimodal analgesic approach is the optimal method of reducing the risk of progression to CPSP, and there are a number of analgesic techniques that can be used to reduce the incidence of acute postoperative pain. Of the analgesic techniques used, the most common are multimodal systemic analgesia, thoracic paravertebral blockade, thoracic epidural analgesia, local anesthetic wound infiltration, and more recently pecs blocks and serratus plane blocks. The former three techniques are all associated with drawbacks including technical challenges, high risk of adverse effects, and limited evidence to minimize the progression to CPSP states, whilst local anesthetic wound infiltration has highly variable pain outcomes. Therefore, an alternative, safer, and more effective technique would be ideal.

Local infiltration analgesia (LIA) techniques have been demonstrated to be efficacious in joint surgery, whilst injection of local anesthesia in the serratus plane to target some of the intercostal and pectoral nerves may have some benefit in mastectomy surgery. However, nobody has yet performed LIA around these nerves in breast surgery, and the investigators feel that this has enormous potential.

Inclusion Criteria:

• Undergoing elective or urgent, primary, unilateral mastectomy with or without axillary lymph node dissection
• ASA-PS I-III
• 18-85 years of age, inclusive
• 50-100 kg, inclusive
• BMI 18 - 40

Exclusion Criteria:

• Bilateral mastectomy surgery
• Revision mastectomy surgery
• Inability or refusal to provide informed consent
• Chronic pain state
• Neuropathic pain
• Opioid dependence
• Allergy to local anesthesia
• Allergy to opioids

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