Motor block during patient-controlled epidural analgesia with ropivacaine or ropivacaine/fentanyl after intrathecal bupivacaine for Caesarean section{dagger}

D. J. Buggy*, N. A. Hall, J. Shah, J. Brown and J. Williams

University Department of Anaesthesia and Pain Management, Leicester University and the Department of Obstetric Anaesthesia, University Hospitals of Leicester, Leicester General Hospital, Leicester, UK

{dagger}Presented in part at the Anaesthetic Research Society Meeting, St George’s Hospital, London, November 1998 and at the Obstetric Anaesthetists Association Annual Scientific Meeting, Liverpool, April, 1999.

Accepted for publication: March 30, 2000


    Abstract
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
We compared patient-controlled epidural analgesia (PCEA) with ropivacaine alone or combined with fentanyl in terms of analgesic efficacy, motor weakness and side-effects in patients who had received spinal anaesthesia for elective Caesarean section. ASA I patients received combined spinal–epidural anaesthesia and were randomly assigned, in a double-blind study, into two groups after operation: group R (n=23) received PCEA ropivacaine 0.1%, bolus 5 mg, lockout 15 min, 3 mg h–1 background infusion, and group RF (n=24) received PCEA 0.1% ropivacaine/fentanyl 2 µg ml–1 at identical settings. Pain and satisfaction on a 100 mm visual analogue scale (VAS) and side-effects were noted. Incidence of motor weakness (Bromage grade 1 or higher) was 48% (11/23) at 8 h in group R compared with 13% (3/24) in group RF (P=0.025). Pain scores on movement were lower in group RF at 8 and 12 h and at rest at 6 and 8 h (P<0.05 for each comparison). Analgesic consumption was less in RF (P=0.041), but there was no difference in time to first request for supplementary analgesia. Patient satisfaction with postoperative analgesia (mean (SD)) was higher in RF (79 (23) vs 57 (29) mm, P=0.045). Caution should be exercised using ropivacaine PCEA after spinal bupivacaine for Caesarean section, because its reputed motor-sparing property may be unreliable.

Br J Anaesth 2000; 85: 468–70

Keywords:anaesthetic techniques, epidural; analgesia, patient-controlled; anaesthetics, local, ropivacaine; anaesthetics, analgesics, opioid; anaesthesia, obstetrics


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Analgesic techniques for Caesarean section must be highly effective and yet allow early mobilization to enable these women to care for their babies. While patient-controlled epidural analgesia (PCEA) with local anaesthetics provides good analgesia, it causes motor weakness, limiting postoperative mobilization.1 Ropivacaine, the most recent amide local anaesthetic introduced into clinical practice, reportedly produces less motor weakness than bupivacaine.2 Ropivacaine epidural analgesia after spinal anaesthesia has not been reported. We compared PCEA ropivacaine alone or combined with fentanyl after Caesarean section under bupivacaine spinal anaesthesia, in terms of analgesic efficacy, motor weakness and side-effects.


    Methods and results
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
After obtaining institutional ethics committee approval and written informed consent, 50 women scheduled for elective Caesarean section under regional anaesthesia were enrolled into the study. Excluded were patients other than ASA I, patients for whom a central neuraxial block was contraindicated and those with a history of adverse reaction to any study medication. Patients were briefed preoperatively on visual analogue scales (VAS) and how to operate the PCEA.

After i.v. access had been established and an infusion of crystalloid commenced, all patients had a combined spinal–epidural (CSE) anaesthetic. The epidural space was identified at L2–3 or L3–4 using a loss of resistance to saline technique with the patient in a sitting position. Dural puncture was performed by a needle-through-needle technique with a Whitacre 26G needle; hyperbaric 0.5% bupivacaine 2.6 ml was injected into the intrathecal space. An epidural catheter was then inserted into the epidural space.

When surgery was complete, patients were randomized, by a sealed envelope technique, into one of two groups: group R (n=25) received PCEA 0.1% ropivacaine, bolus 5 mg, lockout 15 min, with 3 mg h–1 background infusion. Group RF (n=25) received PCEA 0.1% ropivacaine/fentanyl 2 µg ml–1, at identical settings to group R. The analgesic regimen was prepared by the anaesthetist managing the patient, who was not subsequently involved in data collection. It was commenced in the recovery room while the spinal block was still effective. Patients and nursing staff were blind to the group randomization.

Pain at rest and on movement (sitting forward) on a 100 mm VAS at 2, 4, 6, 8, 12 and 24 h, satisfaction with postoperative analgesia at 24 h (VAS) and the incidence of nausea and pruritus were recorded by the patients on a four-page individual patient diary. Dermatomal sensory level was noted using ethyl chloride spray at the commencement of the study and at 8 h. Motor block was evaluated using a modified Bromage scale by nursing staff who were familiar with these assessments. If patients had inadequate analgesia, supplementary rescue analgesia with oral codeine 30 mg/paracetamol 500 mg was available. Total PCEA consumption was noted.

Postoperative monitoring consisted of hourly respiratory rate, pulse rate and non-invasive blood pressure measurements for 4 h and thereafter at intervals of 4 h. Hypotension was defined as systolic blood pressure <90 mm Hg. Sedation was assessed on a four-point scale: 0=fully alert, 1=drowsy, eyes closed occasionally; 2=asleep but roused easily on speaking to the patient; 3=profoundly sedated, roused by physical stimulation.

Data were analysed in GraphPad PrismTM, version 2.0. Physical characteristics and satisfaction scores were compared using the unpaired t-test. VAS pain and total analgesic consumption were compared using the Mann–Whitney U-test. Contingency tables were constructed for categorical data and analysed by {chi}2 analysis with Yates’ correction. The prospective study power calculation was based on analgesic data. Previous studies of women after Caesarean section indicated a standard deviation of the order of 30 mm in early postoperative pain scores. We took a VAS reduction of 25 mm to be clinically significant, hence 24 patients were required in each group to give an {alpha} value of 0.05 and a ß value of 0.2.

Although 25 patients were enrolled in each group, only 23 in group R and 24 in group RF were deemed eligible for statistical analysis. One patient was withdrawn from each group because of technical difficulties with the epidural catheter. Another patient’s data were lost from group R because of PCEA provider pump failure. A further two patients were withdrawn from the ropivacaine group at 12 h because of profound, prolonged motor block. They were included in the analysis as the only missing data were at 24 h.

The two groups did not differ in age, weight or parity. Patients receiving ropivacaine alone had significantly higher VAS pain scores at 6 and 8 h at rest and at 8 and 12 h on movement. Total analgesic consumption was less in the RF group than in group R and no patient in RF requested supplementary oral analgesia compared with eight patients in group R (P=0.005). There was no difference in the time to first request for supplementary analgesia. Patients in group RF had significantly higher scores for satisfaction with their postoperative analgesia compared with group R (P=0.045) (Table 1).


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Table 1 Physical characteristics, analgesia, motor weakness and side-effects. All data are expressed as mean (SD) or median (interquartile range) except where stated
 
The incidence of demonstrable motor weakness (Bromage grade 1 or above) was significantly higher (P=0.025) in group R than in group RF at 8 h but not at 12 h. When patients with Bromage grades 2 or 3 were analysed separately, there was no statistical difference. No patient was allowed to walk if any motor weakness was detected. The two patients in group R who were withdrawn at 12 h had fully recovered by 24 h. There was no difference between the groups in sensory level at 8 h. Pruritus was significantly more likely in group RF than in group R (P=0.033), but no patient requested treatment. There were no differences in the incidences of nausea, hypotension or sedation between the groups (Table 1).


    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
This is the first report, to our knowledge, of epidural ropivacaine for continuing postoperative analgesia after spinal anaesthesia. The increasing use of CSE techniques increases the possibility of epidural administration of ropivacaine after spinal anaesthesia with bupivacaine. The principal finding is the unexpectedly high incidence and duration of motor block observed in patients receiving PCEA with ropivacaine. This observation differs from the initial clinical impression of ropivacaine, which suggested a motor-sparing effect.2 However, a study of PCEA epidural 0.125% ropivacaine compared with 0.125% bupivacaine in labour found that they were clinically indistinguishable in terms of motor weakness.3

We chose a background infusion of ropivacaine 0.1%, believing that it would provide an acceptable balance between adequate analgesia and minimal motor block. In retrospect however, it is clear that we failed in this objective because we underestimated the pain produced by Caesarean section in our patients. In a randomized, double-blind study of three solutions of ropivacaine/fentanyl for PCEA after lower abdominal surgery, 0.05% ropivacaine/fentanyl 1 µg ml–1 produced equivalent analgesia to 0.2% ropivacaine/fentanyl 4 µg ml–1. However, the latter group had a 30% incidence of motor block, compared with none in those receiving the lower concentration of ropivacaine.4 Our choice of ropivacaine 0.1% could reasonably have been expected not to aggravate motor weakness. Moreover, recent work has shown that the relative potency of ropivacaine compared with bupivacaine is only 0.6 and the EC50 for the minimum local anaesthetic concentration for ropivacaine in labour is approximately 0.16%.5 Hence, 0.1% ropivacaine should have been even less likely to produce motor block than 0.1% bupivacaine.

Although the difference is statistically significant only when patients with all grades of motor weakness are included, this unexpected finding is clinically important because even Bromage grade 1 weakness precludes ambulation. Inadvertent intrathecal spread of ropivacaine (via the small dural hole created by the spinal component of the CSE) could possibly explain our observations, although there was no suggestion of dural puncture in any of our patients. Indeed, it has been shown that dural puncture with a 26 gauge Whitacre spinal needle before epidural injection (as in the present study) increases the caudal, but not the cranial, spread of epidural local anaesthetics.6

It is also possible that low thoracic placement of the epidural catheter may have been more appropriate. Repeated introduction of boluses of local anaesthetic into the lumbar area may not provide analgesia in the lower thoracic dermatomes, yet accumulation may increase the risk of motor weakness in the lumbar dermatomes. Although there is also greater sensitivity of neural tissue to local anaesthetics during the later stages of pregnancy, this is an unlikely explanation because patients in group RF did not have as much leg weakness as those in group R. However, it is noteworthy that patients in group R received a significantly higher dose of ropivacaine than patients in group RF over the duration of the study, presumably because their analgesia was less satisfactory than in group RF.

An alternative explanation is an interaction between the two local anaesthetics. An experimental model of profound nerve block under spinal anaesthesia found that combinations of amide local anaesthetics could produce unpredictable prolongation of the block. Although the mechanism is unclear, these investigators postulated that local anaesthetics could interact at the sodium channel to prolong effective duration.7 Whether this effect could be more pronounced on motor as opposed to sensory nerves is unknown.

In conclusion, we found a higher incidence of motor weakness after 8 h in patients receiving PCEA ropivacaine compared with a ropivacaine/fentanyl mixture after bupivacaine spinal anaesthesia. The reason for this finding is unclear, but further studies are indicated to clarify the optimum dose regimen of epidural ropivacaine and fentanyl after spinal anaesthesia. In the interim, caution should be exercised when administering epidural ropivacaine after bupivacaine spinal anaesthesia.


    Footnotes
 
* Corresponding author: University Department of Anaesthesia, Leicester General Hospital, Leicester LE5 4PW, UK Back


    References
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Cooper DW, Ryall DM, McHardy FE, et al. Patient controlled extradural analgesia with bupivacaine, fentanyl or a mixture of both, after Caesarean section. Br J Anaesth 1996; 76: 611–5[Abstract/Free Full Text]

2 Muldoon T, Milligan K, Quinn P, et al. Comparison between extradural infusion of ropivacaine or bupivacaine for the prevention of postoperative pain after total knee arthroplasty. Br J Anaesth 1998; 80: 680–1[ISI][Medline]

3 Owen MD, d’Angelo R, Gerancher JC, et al. 0.125% ropivacaine is similar to 0.125% bupivacaine for labor analgesia using patient-controlled epidural infusion. Anesth Analg 1998; 86: 527–31[Abstract]

4 Liu S, Moore J, Luo A, et al. Comparison of three solutions of ropivacaine/fentanyl for postoperative patient controlled analgesia. Anesthesiology 1999; 90: 727–33[ISI][Medline]

5 Capogna G, Celleno D, Fusco P, et al. Relative potencies of bupivacaine and ropivacaine for analgesia in labour. Br J Anaesth 1999; 82: 371–3[Abstract/Free Full Text]

6 Suzuki N, Koganemaru M, Onizuka S, Takasaki M. Dural puncture with a 26-gauge spinal needle affects spread of epidural anesthesia. Anesth Analg 1996; 82: 1040–2[Abstract]

7 Hassan HG, Youssef H, Renck H. Duration of experimental nerve block by combinations of local anaesthetic agents. Acta Anaesthesiol Scand 1993; 37: 285–7