Choice of opioid for initiation of combined spinal epidural analgesia in labour—fentanyl or diamorphine

D. J. A. Vaughan, N. Ahmad, N. K. Lillywhite, N. Lewis, D. Thomas and P. N. Robinson

Department of Anaesthesia, Northwick Park and St Marks NHS Trust, Watford Road, Harrow, Middlesex HA1 3AJ, UK*Corresponding author

Accepted for publication: October 31, 2000


    Abstract
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 Abstract
 Introduction
 Methods and results
 Comments
 References
 
Sixty-two women requesting regional analgesia in labour were allocated to receive a 1.5 ml intrathecal injection as part of a combined spinal–epidural (CSE) analgesic technique. This contained either bupivacaine 2.5 mg plus fentanyl 25 µg (group F) or bupivacaine 2.5 mg plus diamorphine 250 µg (group D). Times of analgesic onset and offset were recorded, motor and proprioceptive assessments made and side-effects noted. Analgesic onset was not significantly different between the groups (group F, 8.0 min; group D, 9.5 min; P=0.3) but time to first top-up request was significantly longer in the diamorphine group (group F, 73 min; group D, 101 min; P=0.003). Motor loss, assessed by the modified Bromage score, was statistically but not clinically greater in the fentanyl group (P=0.01). Maternal hypotension, pruritis, proprioceptive loss, nausea and fetal bradycardia were rare and not severe, and their incidences did not differ between groups. No respiratory depression was observed after CSE. This use of diamorphine was not associated with increased side-effects compared with fentanyl/bupivacaine, and it has a longer duration of action.

Br J Anaesth 2001; 86: 567–9

Keywords: analgesia, obstetric; analgesic techniques, subarachnoid; analgesics opioid, diamorphine; analgesics opioid, fentanyl


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comments
 References
 
The combined spinal–epidural (CSE) technique for initiation of mobile analgesia in labour is now used widely in obstetric anaesthetic practice. It is said to offer the advantages of rapid onset of analgesia via the spinal route with the flexibility of epidural top-ups later in labour or for obstetric procedures. We decided to investigate the possibility of replacing the intrathecal fentanyl usually used with diamorphine to attempt to prolong the analgesic effect without increasing the incidence of side-effects.


    Methods and results
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 Abstract
 Introduction
 Methods and results
 Comments
 References
 
Local ethics committee approval was granted for this study. Over a 3 month period, all women attending our delivery suite in labour and requesting epidural analgesia were informed about the project. Sixty-two women were recruited. All had singleton pregnancies, were at more than 36 weeks of gestation and had a cephalic presentation. Those who had received opioids within 4 h were excluded.

After i.v. access had been secured, the epidural was sited at L2/3 or L3/4 with the patient sitting. Patients were allocated to one of two groups: group F received isobaric bupivacaine 2.5 mg plus fentanyl 25 µg, total volume 1.5 ml (n=32); group D received isobaric bupivacaine 2.5 mg plus diamorphine 250 µg, total volume 1.5 ml (n=30). The appropriate mixture was injected intrathecally through a 26 G Whitacre needle using a needle-through-needle technique. Cerebrospinal fluid aspirates were tested before and after injection, and the time of injection was noted. The attending midwife was unaware of the group allocation. Pulse, blood pressure and cardiotocograph recordings were carried out as normal.

The times to the first comfortable contraction (freedom from pain regardless of block height; t1) and to first top-up request (t2) were recorded by the midwife. Patients were told to inform their midwife as soon as the pain of contractions recurred. Maternal hypotension (systolic blood pressure less than 90 mm Hg or a reduction of more than 20 mm Hg from baseline or symptomatic), nausea, vomiting, pruritis and fetal bradycardia (less than 100 beats min–1) were recorded and treated if necessary. Proprioception and lower limb power were assessed 30 min after injection using hallux positioning and modified Bromage scoring respectively. All patients were observed every 4 h for 24 h after treatment for evidence of respiratory depression. A respiratory rate greater than 9 b.p.m. was taken as adequate. All subsequent top-ups were opioid-free (0.2% ropivacaine 10–15 ml) to avoid worsening any potential respiratory depression resulting from the intrathecal opioid.

The two groups were similar in terms of age, parity and induction and augmentation rates. Cervical dilation was similar in the two groups (group D, mean 4.0 cm, five patients >5 cm dilated; group F, mean 4.1 cm, seven patients >5 cm dilated). Two women were withdrawn from group D (one analgesic failure, one delivery) and one from group F (analgesic failure). Results from the remaining 59 patients were analysed using the t test, the {chi}2 test, the Mann–Whitney U-test and the Kruskal–Wallis test as appropriate. The results are summarized in Table 1. A P value less than 0.05 was taken as significant.


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Table 1 Results for groups D and F. Data for t1 and t2 are mean (SD). Proprioception data are numbers of patients failing x out of 8 attempts (x=0, 1–3, >=4). Modified Bromage score data are numbers of patients in each scoring category (0, 1, 2, 3). *Significant at (P<0.05)
 
Our results show a clear increase in time to first top-up request in group D compared with group F, with no significant difference in onset times. All episodes of fetal bradycardia were transient and required no treatment. All three episodes of maternal hypotension resolved with 500 ml of crystalloid and, in one case, a 6 mg bolus of ephedrine. Pruritis was more common with fentanyl, but only one patient of the five with pruritis required treatment with i.v. naloxone 200 µg. There were no instances of nausea or vomiting requiring treatment. Proprioceptive deficits were uncommon in both groups but modified Bromage scores revealed significantly greater motor loss in the fentanyl group. There were no cases of respiratory depression detected in the 24 h after drug administration in either group.


    Comments
 Top
 Abstract
 Introduction
 Methods and results
 Comments
 References
 
This study shows that the use of 250 µg diamorphine, when compared with fentanyl 25 µg, given intrathecally with bupivacaine 2.5 mg does not produce a significant increase in side-effects and carries benefit in terms of prolongation of analgesic action. The onset time is similar in the two groups, the difference being 1.5 min or at most one contraction. A difference was noted in power assessment statistically, but clinically all patients were able to mobilize safely.

The CSE is a technique commonly used to initiate labour analgesia. There is ongoing debate in the literature about whether the benefits offered by this approach to the labouring woman above those seen with a low-dose epidural outweigh the perceived small increase in risk associated with deliberate dural puncture.16 This argument has yet to be resolved, but it is clear that an increase in the duration of action of the initial dose results in less breakthrough pain during labour, a factor registered as important in studies of maternal satisfaction.7 The ultimate aim may be a single-intervention method of complete analgesia throughout childbirth, and our study indicates a possible step in the right direction. Decreasing the need for top-ups and associated medical/midwifery interventions may also result in a decrease in staff workload.

The dose of diamorphine used in this study was deliberately low because of worries regarding side-effects, principally pruritis and respiratory depression. Diamorphine was chosen in place of morphine because of its much higher oil/water partition coefficient (morphine 1.4, diamorphine 280, fentanyl 816).8 Doses of 500 µg diamorphine alone have been reported for intrathecal labour analgesia without respiratory depression occurring.9 Morphine has been reported to cause delayed respiratory depression and even apnoea with doses as low as 1 mg intrathecally,8 10 and thus, as a dose of 1–2 mg is reported to be necessary for significant benefit,10 11 it cannot be used reliably and safely in labour. Although we have found no evidence of respiratory depression with diamorphine 250 µg intrathecally, we have not proved conclusively that it will never occur. Care must always be taken in the post-delivery monitoring of these patients.

Recent studies have shown effective analgesia with doses of intrathecal opioid lower than those commonly used.12 It may be that the prolongation of action seen with diamorphine requires less than this 250 µg dose. It may also be that this extension of time to first top-up is increased with a higher intrathecal dose. It seems likely that we have detected an enhanced bupivacaine-sparing effect and that extension of this effect is dependent on local anaesthetic concentration at the effector site combined with improved or prolonged spinal opioid receptor stimulation. To what degree further extension of time to first top-up is possible remains to be elucidated, as does the minimum dose of diamorphine required to produce this effect.


    References
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 Abstract
 Introduction
 Methods and results
 Comments
 References
 
1 Collis RE, Davies DW, Aveling W. Randomised comparison of combined spinal epidural and standard epidural analgesia in labour. Lancet 1995; 345: 1413–6[ISI][Medline]

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9 Kestin IG, Madden AP, Mulvein JT, Goodman NW. Analgesia for labour and delivery using incremental diamorphine and bupivacaine via a 32 gauge intrathecal catheter. Br J Anaesth 1992; 8: 244–7

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11 Leighton BL, De Simone C, Norris MC, Ben-David B. Intrathecal narcotics for labour revisited: the combination of fentanyl and morphine intrathecally provides rapid onset of profound, prolonged analgesia. Anesth Analg 1989; 69: 122–5[ISI][Medline]

12 Lo WK, Chong JL, Chen LH. Combined spinal epidural for labour analgesia—duration, efficacy and side effects of adding sufentanil or fentanyl to bupivacaine intrathecally vs. plain bupivacaine. Singapore Med J 1999; 40: 639–43[Medline]