Determining the Prognostic Value of Continuous Intrathecal Infusion

The purpose of this study will be to determine the efficacy and the prognostic value of a continuous intrathecal prognostic infusion test in an in-hospital setting for selecting patients who would have better long term outcomes for treatment with intrathecal implantable devices. The investigators will compare the primary outcomes [changes in pain intensity score (NRS), patient global impression of change (PGIC)] before and after intrathecal infusion of an admixture of bupivacaine 0.625 mg/ml and fentanyl 1 mcg/ml versus normal saline. The study will include 36 patients with intractable chronic low back pain in the setting of lumbar post-laminectomy syndrome or vertebral compression fracture who failed conservative management and are considered candidates for IDDS. Prior to the implant, the patients will undergo an intrathecal prognostic infusion test with an externalized catheter. Baseline NRS pain scores will be assessed and documented on all patients upon admission to the preoperative area. An intrathecal catheter will be placed in the outpatient procedure suite at the appropriate level for target dermatomes. The needle entry point will occur in the upper lumbar spine and catheter tip will be placed in the lower thoracic spine, under local anesthesia with the patient awake and with minimal or no sedation. The intrathecal infusion will be started using an external pump once patient is in the PACU. The research component is to perform the intrathecal test with normal saline (inactive placebo solution) in addition to a test with fentanyl and bupivacaine (active solution). Patients will be randomly assigned to either Group I (continuous infusion of bupivacaine and fentanyl followed by saline) or Group II (continuous infusion of saline followed by bupivacaine and fentanyl). In PACU, patients will be started on an infusion rate of 0.5 ml/hr and titrated to pain relief greater than 50% of baseline or up to 0.8-1.0 ml/hr within 6-8 hrs after start of the infusion. A clinician blinded to the treatment arm will assess NRS and PGIC on the patients after approximately 12 hours. Assessment will include changes in pain intensity score at rest and upon ambulating or performing maneuvers that normally elicit patient's low back pain. A 4-6-hour washout period will be allotted with infusion of preservative-free normal saline at a rate of 0.2 ml/hr, after which the physician will document a return of the NRS to baseline before switching therapies.