This is a prospective, randomized controlled trial which will be conducted to determine whether sub-dissociative dose ketamine (SDDK) can improve pain control in subjects with chronic pain syndrome presenting to the emergency department with exacerbation of their chronic pain. The investigators also aim to determine whether use of SDDK can reduce the amount of subsequent opioid pain medications required for adequate pain relief in this population.

1. The informed consent process will be initiated by investigators in the emergency department.
2. All potential subjects will be informed that participation in the study could lead to a positive urine drug test that could remain positive for up to a month after the conclusion of the study.
3. Female subjects of child bearing age, will have a pregnancy test performed prior to enrollment; any subjects who are pregnant will be excluded from this project.
4. Each subject will be asked to grade his/her pain severity on a 100mm non-hatched visual analog scale (VAS) ranging from 0 (no pain) to 100 (worst, maximum pain).
5. Each subject will be asked to fill out a baseline pain questionnaire
6. Each subject will be placed on monitors for continuous pulse oximetry, Heart Rate, Respiratory Rate, and blood pressure every 5 minutes for the duration of the study of one hour and longer for any patient who needs continued care. The patients temperature will be taken prior to the start of the protocol.
7. Each subject will have an intravenous catheter placed.
8. Each subject will be sequentially assigned to one of three treatment groups, based on a computer-generated randomization schedule, to receive an intravenous infusion of sub-dissociative Ketamine (0.25mg/kg), sub-dissociative dose Ketamine (0.5mg/kg), or an equal amount of normal saline.
9. All medications will be prepared by an emergency department pharmacist and all study medication intravenous bags will be identical in appearance and will be administered by the emergency department nurse caring for the patient who will be blinded to the study drug.
10. Each subject will receive lightly tinted sunglasses to wear during the duration of the study to minimize bias as ketamine can evoke a tell-tale short- lived nystagmus
11. Each subject will receive the study medication over a 20 minute period via an automated pump. At this point, the subjects will be asked to rate their pain on a VAS and asked if they need additional pain medication that will consist of intravenous hydromorphone with the dose and frequency determined by the discretion of the treating physician and documented on the data collection sheet.

Inclusion Criteria:

• All adult subjects over the age of 18 with chronic pain* presenting to the emergency department with exacerbation of their chronic pain as their primary complaint
• Subjects who are willing and able to provide informed consent. *Chronic pain defined as greater > 3 months of symptoms and an initial VAS pain score > 70

Exclusion Criteria:

• History of overt psychosis, severe hypertension as defined by Systolic Blood Pressure > 180 mm Hg or Diastolic Blood Pressure >110 mm Hg, unstable angina, Coronary Artery Disease, Congestive Heart Failure, porphyrias, thyroid disease, seizure disorder, inability to provide informed consent: dementia, non-English/Spanish speakers, subjects in custody, suicidal, or clinically intoxicated.

Up to 48 hours after study enrollment