Effect of Postoperative Single Dose of Ketamine on Pain After Mastectomy

Inclusion Criteria:

1. Adult women, aged 18 to 80 years old, who will undergo mastectomy.
2. Willing to comply with all study procedures and be available for the duration of the study.
3. Will be scheduled for elective breast surgery for oncologic indication as follows: mastectomy +/- lymph node dissection, prophylactic mastectomy, unilateral or bilateral, with immediate reconstruction
4. No distant metastases.
5. Subject is American Society of Anesthesiologists (ASA) physical status 1, 2, or 3.
6. Subject is medically stable.

Exclusion Criteria:

1. Cognitive impairment (by history) or clinical signs of altered mental status such as confusion, amnesia, disorientation, fluctuating levels of alertness, etc. that may interference with adherence to study procedures and/or participant safety.
2. Past ketamine or phencyclidine misuse or abuse.
3. Schizophrenia or history of psychosis.
4. Known sensitivity or allergy to ketamine.
5. Liver or renal insufficiency.
6. History of uncontrolled hypertension, chest pain, cardiac arrythmia, stroke, head trauma, intracranial mass or hemorrhage or pressure, glaucoma, acute globe injury, uncontrolled thyroid disease, porphyria, or any other contraindication to ketamine. Use of lamotrigine, alfentanil, physostigmine, and 4-aminopyridine are contraindicated
7. Pregnancy or nursing women
8. BMI\>35.
9. Currently participating in another pain interventional trial.
10. Unwillingness to give informed consent.
11. Non-English speaking patients as QoR-15 and BCPQ have not been validated in all other languages