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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.54 no.4 Campinas July/Aug. 2004
Comparison between 0.125% and 0.25% bupivacaine associated to fentanyl for epidural labor analgesia*
Estudio comparativo entre concentraciones de bupivacaína a 0,125% y a 0,25% asociada al fentanil para analgesia de parto por vía peridural
Marcos Emanuel Wortmann Gomes, M.D.I; Vanessa Rezende Balle, M.D.II; Sheila Braga Machado, M.D.III; Florentino Fernandes Mendes, TSA, M.D.IV
do CET/SBA da Santa Casa de Porto Alegre
IIAnestesiologista da Santa Casa de Porto Alegre, Mestranda em Farmacologia pela FFFCMPA, Responsável pelo Núcleo de Analgesia e Anestesia Obstétrica da Santa Casa de Porto Alegre
IIIAnestesiologista da Santa Casa de Porto Alegre
IV Chefe do Serviço de Anestesiologia da Santa Casa de Porto Alegre, Mestre em Farmacologia pela FFFCMPA
BACKGROUND AND OBJECTIVES:
Epidural analgesia aims at decreasing or even abolishing maternal suffering
during labor. It is considered a safe and effective method for pain relief.
This study aimed at comparing two bupivacaine concentrations (0.25% and 0.125%)
associated to fentanyl in epidural labor analgesia to determine its efficacy
on pain relief and its effect on motor block. We have also observed the influence
of these two concentrations on labor duration, fetal outcome and maternal satisfaction.
METHODS: Participated in this prospective and double blind study 51 primiparous women who were randomized to receive one out of two bupivacaine concentrations for epidural labor analgesia (0.25% [n = 23] or 0.125% [n = 28]). Analgesia was measured using a numeric pain scale, and motor block was verified using Bromage scale. Means were compared using Student's t test, while proportions were compared using Qui-square test, with p < 0.05.
RESULTS: There has been no statistical difference in pain, degree of motor block and fetal outcome between groups. Cesarean delivery rate was statistically higher in the group receiving 0.25% bupivacaine (p < 0.05). Lower concentration group patients were more satisfied with the procedure (p < 0.01).
CONCLUSIONS: The association of fentanyl and 0.125% bupivacaine proved to be more beneficial as compared to 0.25% concentration. With this dose, there has been a lower incidence of adverse effects without compromising analgesia, and yet a higher rate of maternal satisfaction.
Key Words: ANALGESIA: labor; ANALGESICS, Opioids: fentanyl; ANESTHETICS, Local: bupivacaine; ANESTHETIC TECHNIQUES, Regional: epidural
JUSTIFICATIVA Y OBJETIVOS:
La analgesia de parto tiene la finalidad de disminuir, o hasta excluir el sufrimiento
materno durante el trabajo de parto, siendo considerada un método seguro
y efectivo para el alivio del dolor. El objetivo de este trabajo fue comparar
dos concentraciones de bupivacaína (0,25% e 0,125%), asociada al fentanil
en la analgesia de parto por vía peridural, cuanto a la eficacia antálgica
y el grado de bloqueo motor, y verificar la influencia de las diferentes concentraciones
utilizadas en la duración del trabajo de parto, en el bien estar del recién-nacido
y en la satisfacción materna.
MÉTODO: En este estudio prospectivo y duplamente encubierto, 51 gestantes primíparas fueron distribuidas aleatoriamente en dos grupos para recibir una de dos concentraciones de bupivacaína para inducción de analgesia de parto (0,25% [n = 23] ó 0,125% [n = 28]). Para la mensuración de la analgesia, fue utilizada la escala numérica de dolor, y para la evaluación del bloqueo motor, la escala de Bromage. Para la comparación de las medias, fue utilizado el teste t de Student, y, para la comparación de las proporciones, el teste Qui-cuadrado, con p < 0,05.
RESULTADOS: No hubo diferencia significativa en las variables dolor, grado de bloqueo motor y bienestar fetal entre los dos grupos. El índice de cesárea fue significativamente mayor en el grupo con mayor concentración (p < 0,05). En el grupo con menor concentración, las pacientes quedaron más satisfechas con el procedimiento (p < 0,01).
CONCLUSIONES: La bupivacaína en la concentración de 0,125%, asociada al fentanil, mostró mayor beneficio cuando comparada con la concentración de 0,25%. En esta dosis, se confirmó menor incidencia de efectos indeseables sin comprometimiento de la analgesia proporcionada y mayor grado de satisfacción materna.
When James Simpson administered ether to a parturient in 1847, he has started one of the most controversial chapters of Medicine, labor analgesia1.
From then on, several methods have been investigated to make pleasant the moment of birth and, with this, to benefit mother/child relationship.
In some centers, approximately 50% of parturients benefit from labor analgesia, which is a safe and effective method for pain relief2.
Several studies were conducted aiming at evaluating the effects of labor analgesia3,4. They have allowed for comparing anesthetic techniques evaluating their advantages and disadvantages in terms of final outcomes such as C-section index and expulsion period duration. More recent studies are trying to find the lowest effective epidural dose aiming at a lower incidence of adverse events5.
It is important to recognize that conclusions reached by several research centers are not necessarily applied to other institutions4. Each hospital and its healthcare team has different practical approaches and experiences making the indication itself of C-section, for example, very subjective. It is difficult to evaluate whether labor analgesia increases the incidence of forceps or whether obstetricians use analgesia to more deliberate apply forceps2. So, each institution should monitor its own statistics about labor analgesia, including different techniques, and about intervention rates, including instrumented labor and C-section.
This study aimed at comparing two bupivacaine concentrations (0.25% and 0.125%) associated to fentanyl for epidural labor analgesia in terms of pain relief and degree of motor block, and at observing the influence of different concentrations in labor duration, neonate vitality and maternal satisfaction.
After the Research Ethics Committee approval and their informed and written consent, a prospective, blind and randomized study was carried out initially considering a sample of 80 patients from Maternidade Mario Totta, Irmandade da Santa Casa de Misericórdia, Porto Alegre. Patients were randomized to receive one out of two treatments: group A - 0.25% bupivacaine and fentanyl (100 µg) or group B - 0.125% bupivacaine and fentanyl (100 µg). Only 51 patients participated in the study: 23 in group A and 28 in group B, since the study was interrupted with agreement of the Research Ethics Committee because results obtained to date had already evidenced advantages for one group.
Inclusion criteria were: a) informed and written consent of patient (or tutor if patient was less than 18 years old); b) primiparous patients, physical status ASA II, aged 15 and 40 years; c) patients in active uterine dilatation with cervical dilatation of up to 7 cm.
Exclusion criteria were counterindications to epidural block.
Patients fulfilling inclusion and exclusion criteria were randomly distributed through a drawing in which 80 pieces of paper were placed within a container - half with letter A and half with letter B - corresponding to groups A or B, respectively.
The following technique was used to obtain a blind study: after history and physical evaluation, investigator 1 would draw to group the patient would belong to, would record it on a specific file only known by him, and would prepare the analgesic solution to be administered by investigator 2, who was blind to drugs used for labor analgesia. Investigator 2 would perform venoclysis with 20G venous catheter and would monitor patient. Then, lumbar puncture with Tuohy 16G needle was performed in L3-L4 until epidural space identification by loss of resistance. After aspiration to be sure of the absence of blood reflux (accidental vascular puncture) or dural perforation, 8 mL of the prepared solution was administered and epidural catheter was inserted until its mark 3 at skin.
Additional 0.125% bupivacaine doses (3 mL) were administered in both groups, whenever patients referred pain higher than 6 in pain numeric scale (asked by investigator 2) and more than 10 minutes after the previous dose.
Data were collected by investigator 2 (blind) and recorded on specific files. Pain intensity was measured by pain numeric scale, that is, a ruler from 0 to 10 was shown to patient who would point to the site equivalent to pain. This point represented a number. Motor block degree was measured by modified Bromage's scale (0 = raises lower limbs; 1 = bend knees; 2 = bend ankles; 3 = does not move lower limbs). Both variables (pain and motor block) were measured 10 minutes after each epidural dose.
Labor evolution was evaluated by uterine dilatation and presentation plane, according to obstetric routine. Fetal vitality was evaluated by Apgar score in the 1st and 5th minute and supplied by the pediatrician. Patients satisfaction was obtained by direct question with the following alternatives: very happy, happy, indifferent, unhappy and very unhappy.
Student's t test was used to compare means and Chi-square test was used to compare proportions, with p < 0.05.
Groups A and B were similar in age, race, prevalence of co-morbidity, cervical dilatation initial presentation and use of oxytocin. There has been no significant difference between groups in pain variables after the first anesthetic solution dose, in number of injections via catheter and fetal vitality (Table I). There has been no motor block for all patients. Although without statistically significant differences in labor, there has been a decrease in expulsion period in the group receiving the lower bupivacaine dose (Table I). Group B patients were happier with the procedure (p < 0.01), as shown in Table II. Table III shows that the incidence of C-sections has been significantly higher in group A (p < 0.05). Crossing satisfaction and C-section variables, it has been observed that 67.7% of very happy patients had vaginal delivery (Table IV).
An ideal design for the scientific community is a randomized, prospective, double blind, placebo-controlled study. Unfortunately, few studies in obstetric analgesia satisfy this standard. So, it is not surprising that several review and meta-analysis studies trying to evidence the benefits of analgesia as compared to possible disadvantages were not conclusive1,2,6. Our study has followed the above criteria, except for the absence of a control group, since it would be anti-ethic not to treat a patient indicated for such.
Randomized clinical trials have helped confirming the clinical impression of anesthesiologists and obstetricians that epidural analgesia poorly influences labor duration and does not increase the risk for C-section1.
In 1993, Eugênio et al. have published the results of labor analgesia in almost 30 thousand patients. They have used 0.25% epidural bupivacaine with 1:200,000 epinephrine without opioids with an initial volume of 6 to 8 mL (0 to 7 cm of cervical dilatation) or 12 to 14 mL (8 to 10 cm of cervical dilatation) and administering additional doses, according to pain. They have concluded that this technique has provided comfort to patients with fast and complete pain relief and not interfering in maternal respiratory and cardiovascular functions, respecting labor physiology and not preventing maternal cooperation during expulsion3. In this study, with this same bupivacaine concentration, its effects have been compared to 0.125% concentration. There has been no difference in analgesia quality and motor block when both concentrations were compared.
In a retrospective study, Parker has observed the outcomes of analgesic techniques using three different concentrations: 0.375%, 0.25% and 0.125% bupivacaine. The incidence of complications, such as dystocia, C-section and instrumented delivery has been lower in the group with the lower concentration (0.125%)7. In a prospective study, Olofsson et al. have found similar results with 0.125% bupivacaine associated to sufentanil, as compared to 0.25% concentration5. There have been no differences in our study between 0.25% and 0.125% bupivacaine in terms of instrumented delivery and pain relief. There has been, however, a higher incidence of C-sections in the higher concentration group.
It is worth highlighting that parturients receiving the lower anesthetic dose were happier as compared with the higher concentration group. Since there has been similar analgesia, one may conclude from this study that pain alone is not the major determinant for maternal satisfaction. In addition, it has been observed that 67.7% of very happy patients had vaginal delivery. It is possible that they have felt more realized with this outcome, since there are expectations during labor, and delivery itself could be considered the "crowning" of efforts during wait.
Today, labor analgesia remains a controversial subject, especially in terms of paradigm to prolong labor or increase the number of C-sections, which does not seem to be true8. Studies in this area have a basic methodological difficulty. These are retrospective studies comparing patients asking for analgesia to those not asking. This generates a selection bias compromising results and, as a consequence, conclusions, that is, characteristics of patients choosing labor analgesia (fear of pain, for example) may also predispose them to the analyzed final outcome (prolonged expulsion period, for example), not making interventions in this group (analgesia) responsible for final effects.
In the conditions of this study, epidural labor analgesia seems to have been more beneficial with 0.125% bupivacaine associated to fentanyl. There has been a lower incidence of undesirable effects without compromising analgesia, which has shown to be effective and safe. After this study, 0.125% bupivacaine associated to fentanyl has become the concentration of choice for epidural labor analgesia in our center.
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Dra. Sheila Braga Machado
Address: Rua Coronel Orlando Pacheco, 96
ZIP: 91440-050 City: Porto Alegre, Brazil
Submitted for publication July 11, 2003
Accepted for publication October 27, 2003
* Received from Maternidade Mário Totta da Santa Casa de Porto Alegre, RS