Effectiveness and acceptability of lidocaine spray in reducing perineal pain during spontaneous vaginal delivery: randomised controlled trialBMJ 2006; 333 doi: https://doi.org/10.1136/bmj.38878.833241.7C (Published 13 July 2006) Cite this as: BMJ 2006;333:117
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Effectiveness and acceptability of lidocaine spray in reducing perineal pain during spontaneous vaginal delivery - Misleading conclusions
Sanders et al conclude that there is no evidence of a significant
reduction in second stage labour pain when lidocaine is sprayed on the
intact perineum prior to a spontaneous vaginal delivery. This is hardly
surprising since the rational for using topical lidocaine (Xylocaine)
spray on intact squamous epithelium, in order to achieve analgesia, is
fundamentally flawed. High concentrations of local anaesthetic, i.e. 40%
lidocaine, are required for absorption through intact skin, and even then
absorption is unreliable and slow 1. Similarly the dose of lidocaine spray
used in this study was minimal, (0.5ml of 10% Xylocaine spray i.e. 50mg
lidocaine). The recommended dose for adequate infiltration analgesia
during delivery is up to four times this amount of lidocaine 2. The
perineal area to which this 0.5ml was applied is not small and this volume
of local anaesthetic spray could never have been expected to reduce the
pain of the second stage of labour.
In addition more than half of the women received pethidine, and
although not specifically targeted at perineal pain, its use could
influence the pain scores and also explain the lack of effect.
Since the lidocaine spray did not reduce the pain in the second
stage, there is no plausible reason why it should influence trauma, by
allowing ‘the more controlled delivery of the fetal head’ as suggested by
the authors. It is thus more likely this is a chance finding, (type I
statistical error), given the multiple endpoints investigated.
It is a concern that this study highlights how ‘acceptable’ this
ineffective technique is to women and midwives when it fails to show a
reduction, and may even have shown an increase in discomfort and pain.
More alarmingly the discussion and accompanying editorial also hint at how
the technique may reduce perineal trauma. The effect of this publication
could result in the technique being adopted by midwives, with the laudable
aim of reducing perineal trauma. The BMJ would have better served it
readers by highlighting that this was a negative study and that the
technique currently has no place in modern obstetric practice.
1 Update in Anaesthesia. Issue 4 (1994) Article 7:p2. The
Pharmacology of Local Anaesthetic Agents.
2 BNF No.51 March 2006. 15.2 Local Anaesthetics. Xylocaine (AstraZeneca)
Competing interests: No competing interests
Sanders et al address an important but neglected topic in their paper
(1), however we have concerns about the measurement of the trial’s primary
outcome. From the information given it appears that perineal pain was
measured using a direct estimation method based on one item, probably a
visual analogue scale.
Our first concern is that a one item measure is prone to measurement
error as the reliability of a scale is related to the number of items it
contains (2). Secondly, direct estimation methods have a response bias
problem known as end-of-scale aversion, where respondents are reluctant to
put responses at the end of the scale (2). These two problems are of
concern in the context of a clinical trial: the effect of a reduced scale
makes it harder to detect differences in scores between groups and the
inherent unreliability of one item compounds the problem.
Thirdly, it is not stated whether any procedures to establish the
validity of the measure were carried out prior to the trial. The most
obvious danger is that the scale is measuring the pain of second stage
labour generally as opposed to perineal pain specifically.
Our final concern is with the estimate of a clinically significant
reduction in pain as 13 scale points or 0.5 standard deviations (1). A
difference of 0.5 standard deviations has previously been suggested as an
estimate of minimally clinically important difference in relation to
health-related quality of life (3), however this is not a universally
accepted rule of thumb (4). Applied to a measure of undocumented validity
and reliability, it may be spurious.
Given the problems outlined above, it is entirely possible a true
difference in perineal pain existed between the two groups but was not
1) Sanders J, Peters TJ, Campbell R. Effectiveness and acceptability
of lidocaine spray in reducing perineal pain during spontaneous vaginal
delivery: randomised controlled trial BMJ doi:10.1136/bmj.38878.833241.7C
2) Streiner and Normal Streiner DL, Norman GR. Health measurement
scales: A practical guide to their development and use. 2nd Ed. Oxford:
Oxford University Press, 1995.
3) Norman GR, et al. Interpretation of changes in health-related
quality of life: the remarkable universality of half a standard deviation.
Med Care 2003, 41:582-92.
4) Beaton DE. Simple as possible? Or too simple? Possible limits to
the universality of the one half standard deviation. Med Care 2003, 41:593
Competing interests: No competing interests