Department of Anaesthetics, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK*Corresponding author
Accepted June 28, 2000
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Abstract |
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Br J Anaesth 2000; 85: 8269
Keywords: anaesthetic techniques, regional; anaesthetic techniques, epidural; anaesthetics local, ropivacaine; anaesthesia, obstetric
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Introduction |
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Ropivacaine has been introduced into clinical practice with the claim that it causes less motor block than bupivacaine.6 7 If true, this raises the possibility of producing the same high quality analgesia, modest motor blockade and high maternal satisfaction with plain ropivacaine as with a low-dose bupivacaine/opioid mixture, thereby avoiding the opioid side effects. The most common bupivacaine/opioid mixture used in the UK is 0.1% bupivacaine with fentanyl 2 µg ml1.1 From minimum local analgesic concentration (MLAC) studies, it can be inferred that 0.2% ropivacaine is the analgesic equivalent of 0.1% bupivacaine with fentanyl 2 µg ml1.810 This concentration of ropivacaine has been used effectively in labour epidural analgesia.11 Therefore, we decided to compare 0.2% ropivacaine with 0.1% bupivacaine plus fentanyl 2 µg ml1 for quality of analgesia, mode of delivery, patient assessment of motor blockade, midwife and maternal satisfaction in a randomised double blind trial.
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Methods |
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All women requesting epidural analgesia were considered eligible for the study, excluding those refusing consent or having allergies to any of the study drugs. After providing informed, written consent, randomization was performed by sealed envelope into one of two treatment groups. Using blinded syringes, patients in the BUPIV group received 0.1% bupivacaine with fentanyl 2 µg ml1, and the ROPIV group received 0.2% ropivacaine. All patients received an initial loading dose of 15 ml, with the first 5 ml acting as a test dose for intrathecal catheter placement. This was followed by an infusion of 8 ml h1 with top-ups of 10 ml as required. Escape top ups of 10 ml 0.25% bupivacaine were prescribed for pain that did not respond to top-ups of the study drugs.
Patient characteristics, procedural, and outcome data were collected using the Wansbeck Epidural Audit System as previously described.12 This computer program generates epidural charts, midwife assessment forms, and patient follow-up questionnaires, whilst simultaneously feeding a database. Mode of delivery, midwife assessment of analgesia, yes/no for complete analgesia at 30 min after the loading dose, and top-up requirements were recorded contemporaneously. Patient visual analogue scores for first and second stage pain, their assessment of motor block, and overall satisfaction with the epidural were obtained 24 h after delivery by an anaesthetist blinded to the treatment regimen.
Data were collated using Microsoft Access Version 2.0 and Excel Version 5.0. Parametric data were compared using two sided, two sample t-tests and non-parametric data were compared using the Mann-Whitney U test. Discrete data were compared by Chi-Square, with odds ratios and confidence intervals calculated where appropriate. Significance level was taken at P<0.05. Statistical analysis was performed on SPSS Version 6.0 for Windows.
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Results |
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Discussion |
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Contemporaneous, hourly visual analogue scores for pain with formal modified Bromage scale motor block assessments might be the academic ideal, but are not feasible in the context of a relatively large study in a busy unit. We argue that subjective assessments of analgesia and motor block, however flawed scientifically, are how patients judge their experience and therefore should be of primary concern.
The focus of this study was to compare the two techniques from the perspective of midwives and patients in the context of a standard technique used in a busy unit. It was never our aim to formally assess pharmacokinetic and dynamic variables such as speed of onset, block heights, and objective motor block. Similarly, we justify the recruitment of all women into this study, regardless of parity and stage of labour, because it is our clinical practice to use a single starting regimen for all women requesting epidural analgesia.
No formal comparisons were made of side effects such as pruritis, nausea, vomiting, and hypotension between the groups. This decision was made because it can be safely assumed that the bupivacaine/fentanyl combination will cause pruritis in a percentage of women, and plain ropivacaine will not. An audit of the incidence of clinically significant hypotension using these treatments revealed such a low incidence that a much larger study would be required to separate the treatments on haemodynamic grounds. Similarly, given that the incidence of nausea and vomiting at some time during childbirth approaches 100%, it would be difficult to assess the causative contribution of the epidurals.
One outcome not considered was the performance of epidurals when converted to anaesthesia for Caesarean section. This is because we have a very low threshold for using spinal anaesthesia despite the presence of an existing epidural in our unit. This policy follows a three year audit showing that all cases of inadequate regional anaesthesia involved topped-up epidurals. Conversion to spinal anaesthesia is not therefore a meaningful measure of epidural performance in our unit.
The principal findings of this study are that 0.2% ropivacaine produces better first stage analgesia than 0.1% bupivacaine with fentanyl 2 µg ml1 and requires fewer routine and escape top-ups. This may be due to the longer duration of action of ropivacaine.13 Whatever the explanation, this challenges our earlier assumption that an opioid is necessary to minimise missed segments, perineal pressure, and to maximise efficacy and satisfaction. The increased motor block in the ropivacaine group was not statistically significant, but the study was probably underpowered for this point. For the size of difference in minimal motor block found in this study, a two sided test to detect a significant difference at P<0.05 with a power of 0.8 would have required the recruitment of at least 800 women. However, even if the ropivacaine regimen did cause more motor block, this did not adversely affect patient satisfaction. Thus another widely held assumption, that satisfaction is strongly related to mobility, is challenged.
This study cannot be used in isolation to make comparative judgements about plain ropivacaine and bupivacaine in labour epidurals. To answer questions about relative motor block effects and overall efficacy requires a comparison of MLAC equivalent plain solutions, such as 0.2% ropivacaine and 0.12% bupivacaine. So, despite the encouraging results in this study, a final judgement on the value of ropivacaine in obstetric practice is not yet possible.
In summary, the results from our study support other work11 suggesting that 0.2% ropivacaine is a suitable choice for labour epidurals. The assumption that an added opioid is always necessary to achieve good analgesia, high maternal satisfaction, and acceptable motor block is challenged and warrants further investigation.
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References |
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