Inclusion Criteria:

- Woman 18 years of age or older.

- Undergoing elective breast surgery for oncologic indication as follows: unilateral or bilateral mastectomy,  prophylactic-mastectomy, +/- lymph node dissection, +/- immediate or delayed reconstruction.

- No distant metastases.

Exclusion Criteria:

- History of cognitive impairment or clinical signs of altered mental status (AMS) that may interfere with adherence to study procedures and/or participant safety. Clinical signs of AMS may include but are not limited to: confusion, amnesia, disorientation, fluctuating levels of alertness, etc.

- Past ketamine or phencyclidine misuse or abuse.

- Schizophrenia or history of psychosis.

- History of post-traumatic stress disorder.

- Known sensitivity or allergy to ketamine.

- Liver or renal insufficiency.

- History of uncontrolled hypertension, chest pain, cardiac arrhythmia, stroke, head trauma, intracranial mass or hemorrhage, glaucoma, porphyria, uncontrolled thyroid disease, or other contraindication to ketamine.

- Lamotrigine, alfentanil, physostigmine, or 4-aminopyridine use.

- Currently pregnant.

- Body mass index (BMI) greater than 35.

- Non-English or non-Spanish speaker.

- Currently participating in another pain interventional trial.

- Unwilling to comply with all study procedures and be available for the duration of the study.

- Patient is American Society of Anesthesiologists (ASA) physical status 4, 5, or 6.

- Patient has started or undergone hormone therapy for gender transition into male.

- Patient scheduled for any bilateral (or greater) flap reconstruction.

Eligibility last updated 5/31/22. Questions regarding updates should be directed to the study team contact.