1 Departments of Anaesthesia and Obstetrics and Gynaecology, Northwick Park Hospital, Watford Road, Harrow, Middlesex HA1 3UJ, UK. 2 Department of Anesthesia, McGill University, 681 Pine Avenue West, Montreal, Canada H3A 1A1. 3 Medical Research Council Clinical Trials Unit, 222 Euston Road, London NW1 2DA, UK *Corresponding author
Accepted for publication: February 26, 2002
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Abstract |
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Methods. A prospective randomized trial investigating the effect of epidural analgesia on the outcome of labour in nulliparae, mothers were randomized to receive either epidural analgesia or meperidine. A questionnaire on postnatal symptoms was sent to them 6 months after delivery.
Results. In all, 611 mothers were studied; 310 were randomly allocated to receive i.m. meperidine up to 300 mg and 301 to receive epidural bupivacaine. The response rate to our questionnaire was 83%. Intention-to-treat analysis showed similar prevalence rates of postpartum backache in the epidural (48%) and meperidine groups (50%), with an observed difference (epiduralmeperidine) of 2% (95% CI, 11 to +6%). After excluding mothers with backache before delivery, there were also similar incidence rates of postpartum backache in the epidural (29%) and meperidine groups (28%), observed difference 1% (95% CI, 8 to +10%).
Conclusions. Epidural analgesia in labour was not associated with an increase in the prevalence or incidence of backache.
Br J Anaesth 2002; 88: 46672
Keywords: anaesthetic techniques, epidural; analgesia, obstetric; analgesics opioid, meperidine; complications, backache
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Introduction |
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The present study is a randomized prospective comparison of the prevalence of backache in mothers who received epidural analgesia compared with mothers who had meperidine. Because other investigators3 4 have noted the coexistence of other symptoms in association with backache, we also enquired about the presence of other symptoms.
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Methods |
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On admission to the labour ward, the diagnosis of labour was confirmed. When requesting further analgesia, the envelope identifying their randomized treatment was opened and mothers were offered analgesia according to their randomization. They either received meperidine 100 mg by repeated i.m. injection (up to three doses), or a lumbar epidural was inserted and, after an initial dose of 0.25% bupivacaine 10 ml, an infusion of 0.125% bupivacaine was administered until the second stage of labour at the rate of 1015 ml h1 with top-ups of 0.25% bupivacaine 5 ml as required (this was the standard epidural analgesia administered on the labour ward at the time of the study commencement). For ethical reasons, the mothers were reassured at recruitment that they could opt out from the trial at any stage.
Twenty-four hours after delivery, the mothers were visited on the ward and asked about back pain and headache before and during pregnancy. For example, Did you suffer from backache? and if yes, Was this during pregnancy, before pregnancy, or both?.
Six months after delivery, a postal questionnaire was sent to the mothers. They were asked about a number of symptoms: frequent backache, frequent headaches or migraines, shoulder symptoms, neck symptoms, urinary incontinence and pain, tingling or weakness in the arms or legs. For each symptom they were asked whether it was present, when it had started and how it affected their daily functioning. For example, they were asked, Do you suffer from frequent backache? and if yes, When did this first start? Was it before you became pregnant, during your pregnancy, or since you gave birth?.
The two randomized groups were compared using MannWhitney U tests and Fishers exact tests where appropriate. Analysis was performed comparing responders and non-responders to the 6-month questionnaire. We compared the groups on the basis of their treatment and also compared characteristics of the women who did and did not have new symptoms at 6 months postpartum.
Stepwise logistic regression was performed to investigate factors influencing the presence of each symptom, either as a persisting symptom or a new symptom 6 months postpartum. Possible predictor variables considered were randomized treatment, maternal age, height, weight, social class, marital status, ethnic group, induced labour, durations of first and second stages, oxytocin administration, mode of delivery, gestational age and foetal weight.
This study was part of a trial investigating the effect of epidural analgesia on Caesarean section rate.5 The prospective sample size of 1168 for the trial had been calculated to detect a reduction in the Caesarean section rate from 7.8% in the epidural group (the observed rate in the unit in 1988) to a rate of 3.8% in the non-epidural group. We calculated that this sample size would also allow us to detect a difference in rates of chronic backache such as that reported by MacArthur and colleagues1 for epidural (19%) and non-epidural (10.5%) with a power >99% and using a significance level of 5%. Recruitment to the trial was slower than anticipated and, of the planned 1168 mothers, 611 were randomized to receive either epidural analgesia (n=301) or i.m. meperidine (n=310) during labour.
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Results |
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Of the 249 women who had been randomized to the epidural group, 219 received their randomized treatment (88%), while of the 259 women randomized to the meperidine group, 194 received their randomized treatment (75%). An intention-to-treat approach was used for the analysis, comparing women on the basis of their randomized treatment allocation. Figure 1 shows the prevalence of backache 6 months postpartum in the two randomized groups subdivided by the mode of analgesia actually received during labour, for mothers who requested further analgesia and were randomized (n=611), returned the questionnaire (n=509) and answered the backache question (n=508).
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Table 4 is a comparison between the two randomized analgesia groups after omitting women who stated 6 months postpartum that the symptoms began before or during pregnancy. There were no significant differences between the two randomized groups in the incidence of any new postpartum symptoms. The incidence of new backache in the epidural group was 29% and in the meperidine group 28%, with an observed difference in the incidence of backache (epiduralmeperidine) of 1.0% (95% CI, 8.2 to +10.3%). Other new symptoms such as headache, neck ache, urinary incontinence, and arm or leg symptoms were reported by around 12% of each group.
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Table 5 compares the characteristics of women with and without new backache at 6 months postpartum, excluding those with backache before delivery. There were no significant differences between the groups in terms of randomized treatment allocated. However, there was a significant difference between groups in the type of analgesia actually received (P=0.02); women with new backache were more likely to have had epidural analgesia. The proportion of non-Caucasian women was higher in those who developed new backache (P=0.02) and the duration of first stage was longer (P=0.001).
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Discussion |
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Our comparison between the two analgesia groups was performed on an intention-to-treat basis as this is the least biased approach.6 There was no significant difference between the groups when they were compared on this basis; the incidence of new backache in the epidural group was 29% and in the meperidine group 28%.
When we compared those with new backache at 6 months with those who had never had backache (Table 5), the type of analgesia actually received was significantly different. Epidural administration was more common in those with new backache (82 out of 101 patients; 81%) than those without (176 out of 259; 68%). This is consistent with the finding of McQuay and colleagues7 who suggest a small but slight increase in the development of new backache after epidural administration. However, this was based on a systematic review of results from non-randomized studies and would therefore incorporate any biases occurring in such studies. In our stepwise logistic regression model, the type of analgesia was no longer a significant predictor after including the duration of the first stage of labour and Caucasian ethnic group in the model. Our findings are similar to those of Howell and colleagues.8
In our study, the prevalence of backache in the meperidine group was 50% and in the epidural group was 48%. This differs considerably from the rate of new backache of 10.5% in the non-epidural group and rate of 19% in the epidural group in the retrospective study by MacArthur and colleagues,1 used in our prospective power calculation. When a post-hoc power calculation was performed for our study, it showed that we would have needed a sample size of 1605 in each group to detect a 5% difference in the prevalence of backache (50 vs 45%) using the 5% significance level with a power of 80%. This is beyond the scope of most institutions and could only be performed in a large multi-centre trial.
The response rate to our questionnaire was high (83%). This compares favourably with the 40% response rate of MacArthur and colleagues1 and the 63% response rate of Russell and colleagues9 and is similar to the 88% response rate of Breen and colleagues.4 Of some concern is the fact that the responders were more likely to be Caucasian and married than the non-responders were. Our study showed a positive relationship between non-Caucasian status and the presence of back pain and other postnatal symptoms such as arm and leg symptoms. It is possible that this effect could be due to non-Caucasian women with postnatal symptoms being more likely to respond than those without postnatal symptoms. However, in a study by Russell and colleagues,9 European and West Indian women were more likely to respond than other groups.
The prevalence of backache at 6 months in our study (49%) is similar to the prevalence of 44% found by Breen and colleagues4 at 2 months postpartum, but considerably greater than the 30% found by Russell and colleagues9 at 12 months. The incidence of new backache at 6 months is somewhat less common (28%) in our study, while that of Russell and colleagues9 was 15% at 12 months. Russell and colleagues study was retrospective but suggests that the prevalence of postpartum backache may be lower at 12 than at 3 or 6 months after delivery. We chose a 6-month follow-up period as back pain is particularly relevant when the mother is weaning her child and possibly planning to return to employment.
There was a higher proportion of non-Caucasian women (35%) who developed new backache compared with Caucasian women (23%). Non-Caucasian women also developed other symptoms postpartum. Our local population, from which the study sample was taken, is comprised of 25% Gujerati Asians. Although theirs was a retrospective study, MacArthur and colleagues10 found that backache, frequent headache, shoulder ache and pains and weakness in the arms and legs all occurred more commonly among Asian than among Caucasian women. Russell and colleagues9 did not report the incidence of new backache with respect to other symptoms or to ethnic group, but did state that, of 36 women seen with new backache, 14 had possible psychological factors related to the backache. Our high prevalence of backache compared with other studies may be due to our study population. MacArthur and colleagues10 postulate that dietary factors may play a role in the prevalence of postpartum problems among Asian women; the cause of backache in Asian women may be of dietary or sociological origin and warrants further investigation.
The mothers gave inconsistent replies to the questionnaires 24 h and 6 months postpartum and this finding draws attention to possible problems associated with the interpretation of retrospectively collected data on postpartum backache. Russell and colleagues9 found that memories even at 18 months postpartum were unreliable. This calls into question the findings of MacArthur and colleagues1 who found an association between epidural analgesia and backache but relied on the mothers memories of events as long as 11 yr previously. In a later prospective study MacArthur and colleagues11 found that although the incidence of low backache was significantly higher in the epidural group than in the non-epidural group on day 1, there was no significant difference at 7 days or 6 weeks.
Our study, like that of Russell and colleagues9, is restricted to nulliparous women. The studies of MacArthur and colleagues1 and Breen and colleagues4 included multiparae. The disadvantage of including multiparae in a study on backache is that back pain may have occurred in relation to a previous pregnancy.
In summary, we have shown that back pain is a common symptom 6 months postpartum and the incidence of new back pain was 28%. In a randomized prospective controlled trial, there was no significant difference in the prevalence between epidural and meperidine groups when an intention-to-treat analysis was used. Women can be reassured that the administration of an epidural per se is unlikely to cause backache.
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Acknowledgement |
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References |
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