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* From the Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, and the
Departments of Anesthesia and
Obstetrics and Gynecology, University of Pennsylvania School of Medicine, University of Pennsylvania Health System.
Address correspondence to: David Hepner MD, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115 USA. Phone: 617-732-8222; Fax: 617-277-2192; E-mail: dhepner{at}zeus.bwh.harvard.edu
| Abstract |
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Methods: Upon requesting analgesia, 50 healthy term parturients were randomized in a prospective, double-blind fashion to receive either CSE analgesia or lumbar epidural analgesia in the labour floor of a university hospital at an academic medical centre. The epidural group (n=24) received bupivacaine 0.0625%-fentanyl 0.0002% with 0.05 ml in 10 ml local anesthetic sodium bicarbonate 8.4% and epinephrine 1:200, 000. The CSE group (n=26) received intrathecal 25 µg fentanyl and 2.5 mg bupivacaine. Additional analgesia was provided upon maternal request.
Results: There were no differences (P > 0.05) in time to perform either technique, motor blockade, or parturient satisfaction or in the number of times that the anesthesiologist was called to perform any intervention. Although the first sign of analgesia was not different between the two groups, the onset of complete analgesia was more rapid with the CSE technique (Visual Analogue Pain Score (VAPS) at five minutes < three: 26/26 vs 17/24, P ± 0.001).
Conclusion: Although epidural analgesia with a low concentration of local anesthetic and opioid mixture takes longer to produce complete analgesia, it is a satisfactory alternative to CSE.
| Introduction |
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| Materials and methods |
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| Results |
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In all cases, the CSE or epidural technique functioned well and there was no need to repeat the technique. Four women (two in each group) delivered before dissipation of the intrathecal dose or the original epidural dose. These parturients were excluded from the additional analgesia data but were included with the rest of the data. There were no accidental dural punctures in the epidural group and none of the parturients in the CSE group developed a postdural puncture headache (PDPH). The incidence of pruritus, nausea, vomiting and hypotension were similar. The amount of ephedrine used to treat hypotension was also similar (Table III
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Four parturients in the CSE group and six in the epidural group required Cesarean section. Two parturients in the CSE group and one in the epidural group required low forceps vaginal delivery. None of the above differences were significant. The reasons for the Cesarean section and low outlet forceps delivery included failure to progress, arrest of dilatation and dystocia. There were no cases of fetal bradycardia or respiratory depression in the mother or fetus. The neonates (n=50) experienced no complications and none were admitted to the neonatal intensive care unit.
| Discussion |
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In an effort to produce motor blockade similar to CSE technique, we opted for a lower concentration of local anesthetic and opioid mixture in the epidural space than in the above studies. We placed the emphasis of our study in comparing CSE with a low dose local anesthetic and opioid mixture epidural technique for labour analgesia with regard to time to perform and number of physician interventions. We chose to place greater emphasis on these two issues because time efficiency is a current economic concern and none of the previous studies had addressed this question.
These concentrations of local anesthetic and opioid for epidural analgesia were chosen (bupivacaine 0.0625%-fentanyl 0.0002%) based on our experience and on previous studies that have demonstrated good analgesia and minimal motor blockade when using this mixture for epidural infusion.5,6 We felt it important to choose an epidural solution that would avoid motor blockade. While probably not equipotent to the CSE solution, this epidural solution achieved similar levels of analgesia as intrathecal fentanyl with bupivacaine. The 25 µg fentanyl dose in the CSE technique was chosen based upon clinical impression of efficacy and duration of analgesia. A recent study to determine the dose-response relation of intrathecal fentanyl for labor analgesia confirms this opinion.15 While the ED50 of intrathecal fentanyl was 14 µg, additional duration of analgesia was obtained by increasing the dose to 25 µg. The authors' conclusion was that there was little benefit in increasing the dose beyond 25 µg. The addition of bupivacaine to the intrathecal fentanyl prolongs its duration with no additional motor block.2
Our use of high volumes of a very low concentration of local anesthetic combined with fentanyl, epinephrine and bicarbonate for the first injection in the epidural group may account for the relatively fast onset of analgesia. This may also explain the similar duration of action of both techniques. All 26 of the CSE patients had VAPS < 3 at five minutes while only 17 of 24 in the epidural group had VAPS < 3 at 15 min. Proximity of drug to nerve in the CSE approach probably accounts for the difference in pain scores. The site of action of intrathecal lipid soluble opioids is believed to be spinal as well as supraspinal.16 Lipid soluble opioids such as fentanyl also penetrate the dura following lumbar epidural administration and, as such, may reach cerebrospinal fluid (CSF) concentrations similar to those after intrathecal injection.17 The slower onset of action of fentanyl given by the epidural rather than the intrathecal route may be because it must penetrate the dura to reach its site of action. Even though the CSE group initially obtained greater degree of analgesia, satisfaction was equal and excellent in both sets of mothers from shortly after the initial injection to the end of the study. We believe this is because all parturients achieved a satisfactory degree of analgesia without motor blockade.
Our study may be criticized for not taking into account the total time from parturient request for pain relief to achieving satisfactory analgesia. We did not delay the initiation of epidural or CSE analgesia to prepare the solutions. While one anesthesiologist was placing the needle, another was preparing the solution. This time must be taken into consideration if a solo practitioner attempts to repeat our results. In this case, the individual must prepare the epidural solution prior to injection, which would add approximately two minutes.
Another criticism to our study is the use of high volumes of local anesthetic, opioid and epinephrine through the epidural needle. The main reason we injected all of the solution through the epidural needle was to have two groups with untested epidural catheters. The epidural solution was injected over a three minutes period and a very careful monitoring of the parturient's response and of the vital signs was taking place at that time. This fractionation may account for the longer latency to onset compared with that of the intrathecal route. We believe that if the medication had ended up in the subarachnoid space or intravenously (iv), it would have been recognized prior to the full amount being injected. A further question regards accidental injection of 10 mg bupivacaine and 32 µg fentanyl intrathecally (IT) or iv. 32 µg fentanyl is safe in either space as long as maternal respiration is monitored adequately. Bupivacaine, 10 mg iv, is well below the toxic dose and IT will produce a spinal block that would be recognized by an anesthesiologist. We are not advocating the injection of the entire solution through the epidural needle or the injection of high concentrations of local anesthetic. Our usual approach is to inject an initial test dose with a local anesthetic and 15 µg epinephrine through the catheter and wait three to five minutes before further injection through the catheter to avoid accidental subarachnoid block or intravenous injection.
Overall, the incidence of side effects was very similar between the two groups. We did not find a difference in the incidence of pruritus unlike earlier studies. We believe that this is because of the substantial concentrations of opioid used in the epidural bolus and in the infusion mixture. Overall, with the exception of a slower onset to complete analgesia, the epidural mixture produced a similar clinical profile to CSE. Is the faster onset of complete analgesia worth the extra cost of a spinal needle and the potential for an increase of side effects? Our impression is that the difference in speed of onset of CSE over epidural injection is measurable but unlikely to be of clinical importance.
Our results indicate that there is no difference between the CSE technique and an epidural technique using bupivacaine 0.0625% combined with fentanyl, epinephrine and bicarbonate in regard to time to perform the block or number of interventions by a physician. Although the epidural group took a longer time for complete analgesia, once it was achieved, it provided a similar clinical profile to the CSE.
Accepted for publication November 27, 1999.
| References |
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