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Re: Can the null hypothesis be accepted?
- Yoshitaka Kawaraguchi (19 December 2006)
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Can the null hypothesis be accepted?
- Christos K Dragoumanis, George I Vretzakis Professor of Aneathesia. Dpt of Anaesthesiology. University of Thessaly- Medical School, Larissa, Greece (7 December 2006)
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Re: Caudal fentanyl and Intravenous pentazocine in children
- Yoshitaka Kawaraguchi (7 December 2006)
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Caudal fentanyl and Intravenous pentazocine in children
- Pradeep Orakkan (27 November 2006)
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Yoshitaka Kawaraguchi
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To the Editor Thank you for the opportunity to reply to Dr. Dragoumanis’s letter. As stated in our article, we calculated a power analysis with alpha of 0.05 to achieve a 95% chance of rejecting (β=0.05) the null hypothesis (group S patients would require a rescue analgesic medication within 8 h and group F patients would require within 16 h, SD=5 h). That is, power of our comparison is 0.95. Thus, we think that sample size calculation of our manuscript is adequate. On the other hand, whether our null hypothesis is acceptable or not is a very difficult question. That is problem we cannot avoid in clinical research. Finally, we have to leave it to readers’ judgment. We do not think that two hours of effective analgesia are clinically significant. Moreover, in order to demonstrate that the difference is statistically significant, total 200 patients would be required (α=0.05, β=0.2). In our opinion, considering a lot of time and effort, it is questionable to study the analgesic advantage of caudal 1μg kg-1 fentanyl further. Conflict of Interest:None declared |
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Christos K Dragoumanis, Anaesthesiologist Universty Hospital of Alexandroupolis - Alexandroupolis, Greece, George I Vretzakis Professor of Aneathesia. Dpt of Anaesthesiology. University of Thessaly- Medical School, Larissa, Greece
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Editor - We read with interest the study by Kawaraguchi and colleagues [1] in which they evaluated the impact of addition of 1μg ∙kg-1 fentanyl to single shot caudal block with ropivacaine 0.2%, 1ml ∙kg-1 on the postoperative analgesia after surgical procedures below the umbilicus in children. Authors report no significant differences in pain scores and duration of analgesia and between group F (ropivacaine 0.2%, 1ml ∙kg-1plus fentanyl 1μg ∙kg-1) and group S (ropivacaine 0.2%, 1ml ∙kg-1) and conclude that the addition of fentanyl 1μg ∙kg-1 to ropivacaine 0.2% for single shot caudal analgesia provides no further analgesic advantages over ropivacaine 0.2% alone. However, the difference in mean duration of effective analgesia between two groups is about two hours (group F: 836 min, group S: 734 min). These two hours of effective analgesia are clinically significant to our opinion and favors co administration of ropivacaine and fentanyl. Moreover performing a power analysis for comparison of duration of effective analgesia between two groups (NCSS and PASS Number Cruncher Statistical Systems. Kaysville, Utah) we found that actual power of this comparison is only 0.09 (β=0.91). A comparison between two treatments must have power of at least 0.8 to avoid a type II error (accepting the null hypothesis of no difference when in fact there is a difference of the specified size, such as concluding that treatment is not effective when in fact it is)[2]. Consequently the conclusion of Kawaraguchi and colleagues about the impact of addition of fentanyl to ropivacaine on duration of caudal analgesia is very probable erroneous as a result of insufficient sample size. Insufficient sample size is a result of inadequate power analysis and design of a study. Furthermore authors did not report enough data about the target power set during the power analysis. References 1.Kawaraguchi Y, Otomo T, Ota C, Uchida N, Taniguchi A, Inoue S. A prospective, double-blind, randomized trial of caudal block using ropivacaine 0.2% with or without fentanyl 1 {micro}g kg-1 in children. Br J Anaesth 2006; 97: 858-61 2.R. H. Riffenburgh, ed. Sample size required for a study. In: Statistics in medicine, second edition. Elsevier, 2006;115-24 Conflict of Interest:None declared |
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Yoshitaka Kawaraguchi
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We thank Dr. Orakkan for his comments on our paper. It is interesting that girls were asking more analgesia than boys in the previous report. All subjects in our study were boys, thus our results may be limited in boys but not in children. As Dr. Orakkan mentioned, it is possible that the analgesic requirement vary with the type of surgery. We think that it would be more desiable to study just subjects undergoing hypospadias repair. However, it was not avoidable to use subjects undergoing surgical procedure other than hypospadias repair, because of the limitation of the study period and the results of sample size calculation. But, the contents of type of surgical procedure in both groups were similar. Thus, we do not think that this limitation affected the study results very much. As Dr. Orakkan menioned, NSAIDs are commonly used as the postoperative analgesia. In Japan, although paracetamol or ibuprefen is not commercially available, rectal diclofenac sodium or acetoaminofen are used (1). The reason why we chose pentazocine but not NSAIDs as a postoperative analgesic in our study is that we just followed the institutional standard protocol for paediatric urological surgery . There are some reports about the analgesic efficacy and complications of intraoperative pentazocine in children (2-4). In our clinical practice, intravenous pentazocine is effective for postoperative analgesia even in the fentanyl administered patients during the anaesthesia. We think the analgesic effect of pentazocine is superior to the antianalgesic effect as a partial agonist when the patients complain of pain. Furthermore, we think the use of pentazocine does not increase the incidence of nausea and vomiting very much (4). Thus, we think that the use of pentazocine for postoperative analgesia instead of the NSAIDs did not affect the results very much. References 1. Yamamoto I, Yukioka H, Fujimori M. Clinical study of postoperative sedation in pediatric patients-effects of inhalation anesthetics and postoperative analgesics. Masui 1994; 43: 1191-5. 2. Ray AD, Gupta M. Clinical trial of pentazocine as analgesic in paediatric cases. J India Med Assoc 1994; 92: 77-9. 3. Hamunen K, Olkkola KT, Seppala T, et al. Pharmacokinetics and pharmacodynamics of pentazocine in children. Pharmacol Toxicol 1993; 73: 120-3. 4. Kawaraguchi Y, Miyamoto Y, Fukumitsu K, et al. The effect of ketamine on reducing postoperative agitation after sevoflurane anesthesia in pediatric strabismus surgery. Masui 2002; 51: 1343-8. Conflict of Interest:None declared |
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Pradeep Orakkan, Spr-Anaesthetics The James Cook University Hospital,
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It is interesting to notice that there is no difference in the quality of analgesia if we add fentanyl to 0.2%ropivacaine for caudal block.I am not sure whether I will be able to follow this findings in my clinical practice.I appreciate the author’s recommendation for the need for further study on the safety profiles and the the dose reponse characteristics of fentanyl added to the ropivacaine for caudal block.In the previous studies it had been mentioned that the lipid soluble drugs given epidurally can produce analgesia not only because of local action but by systemic absorption[1].Fentanyl1mic/Kg is a reasonable dose to start with as the analgesic dose even for systemic use. It is worth finding out the difference between the number of boys and girls complain of pain as in one study[2] they found out that among children aged more than 10 years, girls were asking more analgesia than boys.The analgesic requirement vary with the surgery. So it would have been wiser if study is conducted in children undergoing the same surgery. I accept that penatzocine produces analgesia with little respiratory depression.But pentazocine is a partial agonist.. As the children have already received fentanyl I am not surprised if there is an interaction between fentanyl and pentazocine which may reduce the quality of post operative analgesia. More over pentazocine is rarely used because of the frequent side effects like nausea,vomiting,hallucinations and dysphoria.This can make children umcomfortable and affect the parameters measured.It is not clear why the more commonly used drugs like paracetamol or ibuprefen was not given as the rescue medication before pentazocine. References 1.Bernards, Christopher M Recent insights into the pharmacokinetics of spinal opioids and the relevance to opioid selection. Current Opinion in Anaesthesiology. 17(5):441-447, October 2004 2.Kart T, Rasmussen M, Horn A, et al. Management of postoperative pain in children undergoing orthopaedic surgery. J Pediatr Orthop. 1996;16:545–548 Conflict of Interest:None declared |
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