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May 24, 2007 Pain Pump
Abstract ? Objectives. Over the past few years, there has been an increased reliance on the intrathecal delivery of drugs for patients suffering from intractable pain. We sought to demonstrate the effectiveness of the intrathecal pain pump by examining self-reported pre- and post- implantation pain levels. ? Methods. 84 patients who had elected to implant a Medtronic Synchromed 1 or 2 system in order to control their pain were asked to complete a survey. The survey consisted of pain ratings before implantation, pain ratings post-implantation, medications used before and after implantation, and patient satisfaction with the procedure. ? Results. Perceived success rate for implantation is 68% when measured by the ability to reduce reliance on oral medication. When measured by willingness to undergo the procedure again, the success rate is 86% ? Conclusions. Overall, the implantation of an intrathecal pain pump is an effective way for most people to manage their intractable pain and reduce reliance on oral medications. ? INTRODUCTION ? The last two decades have seen an increased reliance on the intrathecal delivery of drugs for patients suffering from refractory pain (1, 2). Implantation of an intrathecal pump is often done when conventional pain management has failed (1,2,3).? A review of the literature indicates that there have been many studies purporting the effectiveness of intrathecal drug administration.? However, most of these studies are retrospective and involve a small number of subjects (4,5,6,7,8,9).? Corrado, Gottlieb and others (10) conducted a quasi-experimental study that generally supported the efficacy of intrathecal drug administration.? In that study a group of chronic back pain patients who received intrathecal drug therapy were compared with a group who were maintained on oral pain medication. Although this study generally supported the efficacy of intrathecal drug administration it had several limitations, which included a small sample size and lack of randomization. In addition patients self selected intrathecal drug therapy or oral medication.? At present there has only been one randomized study on intrathecal drug therapy conducted by Smith and others (11). This study involved 202 cancer patients from various hospitals.? In this study patients were randomly assigned to either an intrathecal drug therapy or a conventional treatment. The study concluded that patients who received intrathecal drug therapy reported significantly lower levels of pain compared to patients who received conventional pain management. However this study’s conclusion may not be warranted because randomization was broken. Patients in the conventional pain management group were allowed to cross over into the intrathecal drug therapy group if they so desired. Additionally, patients were screened through a morphine injection trial and only patients who responded favorably were assigned to the intrathecal drug therapy group. This present study was an attempt to test a number of specific issues and problems in the field.? The first issue was whether or not there was a difference in pain level for pre/post implantation of an intrathecal infusion pump.? In addition, two issues which were not dealt with in prior research were also examined. These were whether or not there was a relationship between pain reduction and the ability to reduce reliance on oral pain medication and whether or not the patients would repeat the procedure of intrathecal pump implantation. ? ? PROCEDURES Subjects All subjects were chronic pain patients who were receiving intrathecal drug therapy. All patients had been implanted with either the Medtronic Synchromed 1 or 2 systems.? Subjects were asked to volunteer to complete a survey about intrathecal drug administration. Eighty-four participants (26 males and 58 females) were included in this study. This clinic had implanted a total of 102 intrathecal pumps. At the time this study took place, eight of the patients were deceased and ten of the patients either refused to participate or provided unusable data. Thus, the eighty-four participants represent an effective 89% response rate (84/94). ? ? Procedure ??????????? The total number of patients who had been implanted with an intrathecal pain pump was determined by reviewing medical records. These patients were identified and asked to volunteer by filling out a survey about intrathecal drug delivery. The survey consisted of the following components: 1. Pain ratings before implantation (visual analog scale 0-10) 2. Pain ratings post-implantation. 3. Medications used before and after implantation for the purpose of determining medication reduction. 4. Patient satisfaction and whether they would undergo the procedure again. All surveys were completed in July of 2006. ? RESULTS Subjects Eighty-four participants (26 males and 58 females) were included in this study. The participants ranged in age from 36 to 90 years old (M = 59.46, SD = 12.43). The majority of participants (of those who reported their ethnicity) were Non-Hispanic White (42 participants, 76%). Five (9%) of the participants were Hispanic. The following ethnicities were represented by three or fewer participants: African-American, American-Indian, Black-Hispanic, and Korean-American. The remaining 31 participants failed to state their ethnicities. Mean reported pain duration was 16.13 years (SD = 11.62). All relevant means and standard deviations are shown in Tables 1, 2, and 3. Minor variations in sample size are due to occasional skipped or illegible responses. Pain scale comparisons The mean recalled pre-implantation pain score was 9.12 on a 10 point scale (SD = 1.05). Mean recalled post-implantation pain score was 5.64 (SD = 2.28). This drop in perceived pain level is significant (F(1,83) = 189.27, p <.0005). By Cohen’s (12) conventions, the effect size is large, accounting for 70% of the variance (η2 = .70). Table 4 shows the percent change of perceived pain level. The first column shows the percent change for patients who perceived a reduction of 50% or better. The second column shows the number of patients who achieved each level of pain reduction. The third column shows the cumulative percent of patients at each pain reduction level. (The remaining columns show corresponding values for patients who failed to perceive a 50% pain reduction.) As seen in this table, 40.5% of the patients perceived a pain reduction of 50% or better. All data were gathered during June, 2006. This strategy allows analysis of perceived pain relief over time. The length of time between the date of implantation and the date of data collection ranged from three to 149 months (M = 60.80, SD = 39.35, MED = 55.00). The correlation between percent change of perceived pain level and number of months since implantation is statistically significant (r(83) = -0.25, p < .05). This correlation indicates that there was some reduction of pain relief over time. However, although the correlation is statistically significant, the magnitude of this effect is small, accounting for only 6.25% of the variance. ? ? Success/failure comparisons Two of the questions on the questionnaire provide an indication of perceived success or failure of the implantation. Participants were asked: “Were you able to reduce your reliance on oral pain medications?” and “Would you have the pump implanted again?” Sixty-eight percent of the participants (54/79) indicated that they were able to reduce reliance on oral medications. Eight-six percent (69/80) said that they would have the pump implanted again. Thus, the perceived success rate is 68% by the first criterion and 86% by the second. Two analyses were undertaken to examine differences between the success and failure participants. A 2 x 2 mixed model ANOVA, with time (pre, post) as a within subjects factor and success/failure as a between subjects factor, was performed. This analysis used ability to reduce reliance on oral pain medications as the success/failure criterion. The analysis yielded significant main effects for both success/failure (F(1,77) = 50.42, p < .0005, η2 = .18) and time (F(1,77) = 151.36, p < .0005, η2 = .66). The success/failure x time interaction was also significant (F(1,77) = 25.58, p < .0005, η2 = .25). The interaction is shown in Figure 1. It shows that the success participants achieved substantially more pain reduction from pre-implantation to post-implantation than did the failure participants. A 2 x 2 mixed model ANOVA, with time (pre, post) as a within subjects factor and success/failure as a between subjects factor, was performed. This analysis used willingness to implant the pump again as the success/failure criterion. The analysis yielded significant main effects for both success/failure (F(1,78) = 20.20, p < .0005, η2 = .21) and time (F(1,78) = 52.21, p < .0005, η2 = .40). The success/failure x time interaction was also significant (F(1,78) = 26.42, p < .0005, η2 = .25). The interaction is shown in Figure 2. It shows that the success participants achieved substantially more pain reduction from pre-implantation to post-implantation than did the failure participants. Sex comparisons A 2 x 2 mixed model ANOVA, with time (pre, post) as a within subjects factor and participant sex as a between subjects factor, was performed. This analysis showed only the time main effect as a significant factor (F(1,80) = 162.36, p <.0005; η2 = .67). Neither the main effect for sex (F(1,80) = 3.38, p > .05) nor the time x sex interaction (F(1,80) = 0.00, p > .05) was significant. Summary In sum, the perceived success rate for this procedure is 68% when measured by the ability to reduce reliance on oral medication. When measured by willingness to undergo the procedure again, the success rate is 86%. Successful participants were able to attain substantially more pain reduction than failure patients when success is measured by either criterion. There were no significant sex differences. DISCUSSION? This present study differed from other studies in the field because it had a larger sample size and it attempted to address issues which have not been previously dealt with in prior research. The results of this study show that patients implanted with intrathecal infusion pumps showed significant reduction in pain levels.? The study also showed that the patients who were judged to be successful were better able to reduce their reliance on oral medications.? In fact, the ability to reduce reliance on oral pain medications was significantly related to pain reduction.? Patients who were not able to achieve satisfactory pain relief from intrathecal drug infusion were less able to reduce their reliance on oral medications.? In this study success was defined by the patient’s ability to reduce pain and reliance on oral medication.? On the other hand, failure was defined by the inability to reduce pain and drug consumption.? In other words, those who could not reduce drug consumption could be considered failures.? An interesting finding from this study was that patients who said that they would be re-implanted were ones who experienced pain relief and were able to lower their reliance on oral medications. Patients who did not experience pain relief or were not able to lower their use of oral medications were more likely to say, when asked, that they would not have the intrathecal pump implanted again. ? These findings suggest that intrathecal drug therapy can help patients in lowering their reliance on oral pain medication. Intrathecal drug administration is judged to be superior to oral medication because drugs delivered intrathecally do not have to pass to the liver and significantly less medication is needed.? ? Although this study supported the efficacy of intrathecal drug administration it suffered from several limitations.? Like most studies in this area it is a retrospective study where patients were asked to rate their perceived pain level.? A patient’s judgment about their pre and post pain level could be affected by cognitive dissonance.? Future research should address personality or environmental variables that predict successful and unsuccessful patients.? It is also important to address the issue of actual oral medication reduction.? Another important issue that has not been dealt with in most research studies is what drugs and what dose of that drugs in the intrathecal pump predicts a patient’s success.? Yet another important issue is to look at whether or not one particular drug works best in lowering pain levels.? Finally one other question that needs to be answered is whether different oral medications are affected differently when combined with intrathecal drug administration. ? ? ? References: ? ? 1. Corrado PE, Varga CA, Concannon DM. Is intrathecal drug therapy an effective treatment for chronic pain? AJPM 2005; 15:33-37. ? 2. Bennett G, Serafini M, Burchiel K, Buschser E, Classen A, Deer T et al. Evidence based review of the literature on intrathecal delivery of pain medication. J of Pain Symptom Management 2000; 20:S12- 36. ? 3. Coombs, DW, Saunders RL, Gaylor MS, Pageau MG Leith MG Schaiberger C et al- Relief of continuous chronic pain by intraspinal narcotics infusion via an implanted reservoir. JAMA 1983; 250:2336-9. ? 4. Hassenbusch SJ, Pillay PK, Magdinec M, Currie K, Bay JW, Covington EC, Tomaszewski? MZ. Constant infusion of morphine for intractable cancer pain using an implanted pump. J Neurosurgery 1990; 73:405-9. ? 5. Kanoff RB. Intraspinal delivery of opiates by implantable programmable pump in patients with chronic, intractable pain of nonmalignant orgin. J Am, Osteopath Association 1994; 94:487-93. ? 6. Krames E. The chronic intraspinal use of opiod and local anesthetic mixtures for the relief of intractable pain: when all else fails! Pain 1999; 55:1-4. ? 7. Paice, JA, Penn RD and Shott S Intraspinal Morphine for chronic pain: a retrospective, multicenter study.? J of Pain and Symptom Management 1996; 11:71-80. ? 8. Van Buyten JP- Outcomes of intrathecal morphine. Presented at the Advanced Interventional Pain therapies meeting in Tenerife, Spain. 1998. ? 9. Yaksh TL, Onofrio BM Retrospective consideration of the doses of morphine given intrathecally by chronic infusion in 163 patients by 19 physicians.? Pain 1987; 31:211-23. ? 10. Corrado P, Gottlieb H, Varga C, Abdelhamid M, Greguso V- The effect of intrathecal morphine infusion on pain level and disability in pain patients with chronic intractable low back pain. AJPM 2000; 10: 160-166. ? 11. Smith T, Staats P, Deer T, Stearns L, Rauck R, Boortz-Marx R, et al. Randomized clinical trial of an implantable drug delivery system compared with comprehensive medical management for refractory cancer pain: impact on pain, drug-related toxicity, and survival.? Journal of Clinical Oncology 2002; 20:4040-9. ? ????????? 12. Cohen J.? Statistical Power Analysis for the Behavioral Sciences, 2nd ed., Hillsdale, NJ:Lawrence Erlbaum Associates, Inc., 1988. ? ? Table 1 Means and Standard Deviations for Variables as a Function of “Were you able to reduce your reliance on pain medications?” ?
? ? Table 2 Means and Standard Deviations for Variables as a Function of “Would you still have the pump implanted?”
? Table 3 Means and Standard Deviations for Variables as a Function of Subject Sex
? ? Table 4 Cumulative Percent of Change in Pain Level
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