The purpose of this study is to:

1. Establish whether ketamine can decrease opioid consumption and modulate the onset of opioid tolerance and prevent opioid-induced hyperalgesia in pediatric subjects, ages 10 years to 18 years, undergoing posterior spinal fusion and instrumentation.

Inclusion Criteria:

1. The subject is 10 to 18 years of age
2. The subject's American Society of Anesthesiologists physical status is ASA 1, 2 or 3 (see appendix I)
3. The subject is scheduled for elective posterior spinal fusion and instrumentation.
4. The subject's parent/legally authorized guardian has given written informed consent to participate

Exclusion Criteria:

1. The subject has a history or a family (parent or sibling) history of malignant hyperthermia
2. The subject is pregnant or nursing.
3. The subject has known significant renal disorders determined by medical history, physical examination or laboratory tests
4. The subject has a known or suspected allergy to morphine, remifentanil or ketamine
5. The subject is an ASA classification of 4 or greater (See Appendix I)
6. The subject is scheduled for a surgical sub-procedure (i.e. anterior spinal fusion)
7. The subject is unable to self-administer morphine using patient-controlled analgesia (PCA) pump
8. The subject had a recent opioid exposure (within 1 month of surgery)
9. The subject is obese (body mass index >30kg/m2)
10. The subject is planned for elective postoperative ventilation
11. The subject has a known ocular disease not permitting pupillometric examination
12. The subject has used any investigation products in the past 30 days

ASA classifications: ASA Physical Status 1 - A normal healthy patient ASA Physical Status 2 - A patient with mild systemic disease ASA Physical Status 3 - A patient with severe systemic disease

the duration of the study (96 hrs) post surgery

Patient sex and ethnicity could have led to analytical bias.