Patients adhering to the general selection criteria described previously move to the trial stage of the use of intrathecal medication. Before an implanted pump is used, it is important to perform an adequate trial to assure patient and physician that the long-term administration of intrathecal opiates will be successful.
There is no proven method for trial screening to determine safety and efficacy of the intrathecal treatment. The response to the acute administration of these medications is believed to predict long-term efficacy. The goals of screening are to determine whether the patient has side effects with the drug used and to document pain relief. Just as there are no proven methods of screening, there is no proven length for a screening trial. Single intrathecal bolus dosing, epidural infusion, and intrathecal infusion trials have all been performed and continue to be the predominant techniques utilized.17 Only epidural infusion has decreased in popularity, since it is not now believed to represent the true effects of intrathecal dosing. Bolus intrathecal doses are administered by lumbar puncture, and the patient is monitored for side effects and analgesia. This technique may maximize the side effects of nausea and vomiting and may provoke a higher incidence of urinary retention. Reported pain relief may last up to 24 hours but generally peaks after a few hours. Paice et al. reported that 33.7% of 429 physicians in a retrospective review used this method at some point.17 Many practitioners do not think the bolus dosing technique can control for placebo effects, although few physicians believe that a blinded placebo trial is necessary.25 Even so, Paice et al. reported that 18.3% of the physicians still used this method.17 It is not appropriate, however, to deny a patient implantable pain therapy based on a prior placebo response.26-29
The screening trial seeks to mimic the effects of chronic administration of the intraspinal analgesic. Epidural catheters placed through a tunneled approach have been used for prolonged trials of days to weeks. Dosing tends to be a factor of 10 times higher than the expected intrathecal dose. This method seems to predict efficacy but may not screen for side effects seen with intrathecal administration. Some clinicians feel that the higher systemic doses associated with this method make it suboptimal for screening. At the time of the Paice article, which was published in 1996, 35.3% of the participating physicians were using this method.
The most frequently used method is said to be the placement of a percutaneous or tunneled intrathecal catheter.30 This technique best predicts the side effect profile and pain relief. It also provides a starting infusion rate for the pump and allows sequential trials of different drugs if the initial drug is ineffective. Intuitively this method closely approximates the response of an implanted drug administration system.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.