A patient with chronic pain that is expected to persist for more than 6 months should be considered for intrathecal opioid therapy. The ideal candidate is one who has already failed conventional narcotic treatment, experienced intolerable side effects, or failed other pain management modalities such as spinal cord stimulation.
A thorough physical assessment, psychological evaluation, and test dose trial must be performed before scheduling the actual surgery for pump placement. Medical history, physical assessment, and appropriate imaging tests allow one to determine the type of pain that the patient is experiencing. Baseline pain rating can be assessed with a visual analogue scale (VAS), numerical pain rating, verbal pain scale, patient and caregiver questionnaires, and pain drawings.
Disease states that would preclude pump implantation should also be identified. Contraindications to implantation generally consist of aplastic anemia, systemic infections, allergies to the metal or plastics used in the pump or catheter, active intravenous drug abuse, and coagulopathies . Psychological contraindications can be identified by commonly used tests, such as the McGill Pain Questionnaire, Minnesota Mutiphasic Personality Inventory (MMPI-2), and the Beck Depression Inventory. Formal psychiatric consultation should be considered.
A trial of intraspinal opioid, either epidural or intrathecal, is used as a mechanism to predict long-term success. A positive response is usually defined as a 50% reduction in baseline pain scores without the presence of intolerable side effects. The trial can be performed by a bolus injection or as a continuous infusion. The exact technique generally depends on the clinician's comfort level and judgment. One of the most common techniques involves insertion of an epidural catheter and gradual titration of continuous morphine infusion until the desired effect is achieved. A trial with continuous infusion mimics a pump more closely. Because the epidural route is associated with larger dosing requirements and more extensive systemic uptake, an intrathecal trial may result in fewer side effects. However, so far there is no evidence that either approach (epidural vs intrathecal, continuous vs bolus administration, opioid only vs placebo controlled) results in higher predictability of subsequent treatment success .
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