Anesth Analg 1999;89:1233
© 1999 International Anesthesia Research Society
REGIONAL ANESTHESIA AND PAIN MANAGEMENT
Transient Paralysis After Intrathecal Bolus of Baclofen for the Treatment of Post-Selective Dorsal Rhizotomy Pain in Children
Iris E. Soliman, MD*,
T. S. Park, MD
, and
Maura C. Berkelhamer, MD*
Departments of
*Anesthesiology, Division of Pediatric Anesthesiology, and
Neurosurgery, St. Louis Children’s Hospital, Washington University School of Medicine, St. Louis, Missouri
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Introduction
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Spastic diplegia or quadriplegia in children with cerebral palsy is caused by damage to the descending inhibitory motor tracts (1). Facilitated anterior horn cells are left unopposed. Bilateral selective dorsal rhizotomy (SDR) of L1-S2 posterior rootlets reduces spasticity and improves motor function (2, 3). Management of post-SDR pain is a challenge because of its multifactorial components. A combination of parenteral opioids (fentanyl) and benzodiazepines (diazepam), with an intrathecal (IT) bolus of fentanyl after dural closure, has been successfully used in our institution for treating post-SDR pain. Baclofen, a gamma amino butyric acid (GABA) agonist, frequently used orally to control spasticity in children with cerebral palsy, is currently being used intrathecally because it has been shown to be nonneurotoxic in primate studies (4). We hypothesized that IT baclofen, instead of fentanyl, might minimize the postoperative requirements for analgesics after SDR. A randomized, double-blinded study, comparing two doses of IT baclofen with IT fentanyl was initiated. Unexpected and unacceptable motor and sensory deficits encountered in two patients who received IT baclofen resulted in premature termination of the study. We conclude that the use of IT baclofen is not suitable for the management of post-SDR pain because of the potential for transient neurological deficits that may interfere with immediate postoperative assessment of motor and sensory function.
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Methods
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After approval of the institutional review board, informed consent was obtained, and patients were randomly assigned to one of three IT drug regimens. Patients were premedicated with oral midazolam (0.5 mg/kg). After inhaled induction with sevoflurane or halothane and established IV access, a fentanyl bolus (10 µg/kg) was given. Anesthesia was maintained with a fentanyl infusion (2 µg · kg-1 · hr-1) and low end tidal concentrations of isoflurane (
1%). An IV diazepam bolus (0.2 mg/kg, maximum 10 mg) preceded electromyographic stimulation. After dural closure, one of three IT drug regimens was injected by the surgeon in a 1-mL tuberculin syringe. These equal volumes of drug regimens given were fentanyl (0.5 µg/kg), baclofen (1.0 µg/kg), or baclofen (1.5 µg/kg). After extubation, the IV fentanyl infusion continued in the postanesthesia care unit (PACU) and overnight in the pediatric intensive care unit (PICU). All patients were transferred to the neurosurgical floor on the first postoperative day. All IV medications were discontinued on the second postoperative day. Thereafter, pain was controlled with oral analgesics and diazepam as needed.
During the monitoring period, several variables were recorded in the PACU, PICU, and neurosurgical ward. These included heart and respiratory rates, blood pressure, and oxygen saturations. Nursing staff assessed pain and sedation levels using the modified Children’s Hospital of Eastern Ontario Pain Scale and sedation scores, respectively. Median pain and sedation scores are reported, whereas demographic data are reported as mean ± SD. We had originally intended to use appropriate nonparametric comparison methods. Because of the abrupt interruption of the study and the small number of patients, statistical analysis was no longer indicated. Side effects attributed to fentanyl or baclofen were also monitored and recorded.
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Results
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Six ASA physical status II patients, three boys and three girls, were randomly assigned to one of the three IT drug regimens. One patient received fentanyl, three received small-dose baclofen (1 µg/kg), and two received large-dose baclofen (1.5 µg/kg). Patient demographics are shown in Table 1.
There were no differences in the median pain scores or sedation levels (Tables 2 and 3) among the study groups. The baclofen groups were combined because of the small number of patients. Two of the three patients who received small-dose baclofen required additional fentanyl and diazepam in the PACU. This might suggest that the large-dose baclofen was initially more effective in relieving pain and spasms.
Twelve hours after admission to the PICU, all patients, regardless of the IT regimen, required IV diazepam to relieve spasms. No fentanyl boluses were required to supplement the infusion for pain control. Infusion rates were decreased to <2 µg · kg-1 · h-1 on the first postoperative day, and discontinued on the second postoperative day. Mean infusion time was 47 ± 3 h.
One patient in each of the large- and small-dose baclofen groups experienced profound muscle weakness immediately postoperatively. The patient who received the small-dose baclofen experienced complete motor and sensory loss in both lower extremities. All deficits resolved within 2 h with no sequelae. These two incidents, however, were sufficient to persuade us to discontinue the study. Other side effects included pruritus treated with diphenhydramine (n = 1), and nausea and vomiting treated with ondansetron (n = 2). One patient, who had a history of difficulty in voiding, required bladder catheterization for urinary retention.
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Discussion
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Spastic diplegia associated with cerebral palsy is related to low birth weight and prematurity. Periventricular leukomalacia occurs after the diminution of blood flow to white matter during cerebral ischemia (1). Fibers descending from the leg area of the motor homunculus are most vulnerable and easily damaged. The loss of suprasegmentary control over the balance between inhibitory and facilitory forces on the anterior horn cells causes reduction in inhibition, resulting in spasticity. Selective sectioning of the posterior rootlets reduces tone and improves motor function in these children (2,3).
Post-SDR pain is multifactorial because of its somatic, hyperesthetic, and dysesthetic components. Opiates have been administered via the epidural (5), IT (6,7), and IV (8) routes for pain control. Benzodiazepines have been combined with opioids when the IV route was used.
GABA is considered the major inhibitory transmitter of the brain and spinal cord. Inhibitory receptors are located presynaptically on primary afferent fibers in the spinal cord dorsal horn. GABA-B stimulation decreases the release of transmitters from primary afferent fibers. GABA agonists, such as benzodiazepines and baclofen, have been used for the treatment of spasticity, the latter, as a GABA-B receptor agonist, depresses mono- and polysynaptic activity in the spinal cord. After being proven to be noneurotoxic (4), baclofen has been used IT in both humans and primates (9,10). It has also been evaluated by Albright et al. (11) for its efficacy as a chronic IT infusion for the control of spasticity in children who are not amenable to SDR.
We hypothesized that a single bolus of IT baclofen, instead of fentanyl, might have a more sustained effect in controlling post-SDR pain caused by spasms, thereby reducing the amounts of supplemental parenteral opioids and benzodiazepines required. The two doses of baclofen 1 and 1.5 µg/kg were extrapolated from the test dose, which is usually used before insertion of baclofen pumps for chronic use.
We have demonstrated that there were no differences in the pain or sedation scores among any of the patients receiving the three drug regimens. The patient who received IT fentanyl followed the usual course of similarly treated post-SDR patients in our institution.1
Immediate assessment of motor function is crucial after SDR. The unacceptable side effects of transient, but profound, motor and occasional sensory deficits in patients receiving IT baclofen make it an undesirable choice of treatment for post-SDR pain. Experience with baclofen for the treatment of spasticity did not involve newly sectioned dorsal roots, making our observations unique regarding its effect under these specific acute conditions.
Although the mechanism of these transient neurological deficits in our study remains unclear, we can only speculate that they were probably results of the direct effect of baclofen on the newly resected pathways of motor and sensory impulses. This effect may also be caused by the alteration of interneuronal responses and GABA-B receptor activity within the spinal cord. Other surgical causes, such as injury of the central motor roots or hematoma, were unlikely because of the transient nature of the neurological symptoms.
We conclude that IT baclofen did not add any benefit to the currently used combination of IT opiates and IV benzodiazepines for post-SDR pain and muscle spasm relief. Moreover, it may interfere with the immediate postoperative assessment of motor function.
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Acknowledgments
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This work was supported by Medtronic, Inc.
The authors thank Heidi Pence, Rebecca Snider, and Linda Lobos for their technical assistance with the preparation of this manuscript.
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Footnotes
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1 Soliman IE, Bantrup G, Cornell-Nevois C, Park TS. A regimen for perioperative pain management of patients undergoing selective dorsal rhizotomy. Abstract presented at: American Academy of Pediatrics, Society of Pediatric Anesthesia; Spring Session February 1996; Tampa, FL. 
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References
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Accepted for publication May 28, 1999.
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