Division of Anesthesiology, Pain Management, Emergency and Critical Care Medicine, University Hospital, Nîmes, France
* Corresponding author: Fédération Anesthésie-Douleur-Urgences-Réanimation, Groupe Hospitalo-Universitaire Caremeau, Place du Pr Debré, 30029 Nîmes cedex 9, France. E-mail: guy.aya{at}chu-nimes.fr
Accepted for publication April 4, 2004.
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Abstract |
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Methods. To assess circadian variations in labour pain perception, 222 consecutive nulliparous women with uncomplicated pregnancy, spontaneous labour, cervical dilatation (35 cm), ruptured membranes and normal fetal heart rate tracings were studied. Visual analogue pain scores (VAPS) were analysed and divided into four periods: night (1:01 a.m. to 7:00 a.m.), morning (7:01 a.m. to 1:00 p.m.), afternoon (1:01 p.m. to 7:00 p.m.) and evening (7:01 p.m. to 1:00 a.m.). VAPS were also compared between daytime (morning+afternoon) and nocturnal (evening+night) periods.
Results. Daytime mean VAPS were lower than nocturnal scores [75.6 (15.1) vs 85.7 (14.1), P<0.0001]. VAPS were lower in the morning than in the afternoon, evening and night periods (ANOVA, P<0.0001).
Conclusion. Labour pain perception appears to be chronobiological, and this might be taken into account when enrolling parturients in studies designed to assess or treat labour pain.
Keywords: analgesia, obstetric ; analgesic techniques, extradural ; measurement techniques, visual analogue ; pain, acute ; pain, mechanism ; pain, psychological variables ; pregnancy
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Introduction |
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Methods and results |
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On inclusion, each parturient was given a visual analogue scale ruler and asked to quantify her pain intensity on a 100-mm straight line printed on one side of the ruler, using a cursor. The left end of the line represented no pain, whereas the right end represented the worst pain imaginable. The other side of the ruler was graduated, so that the anaesthetist could read and record visual analogue pain scores (VAPS), which was the primary study measurement. Parturients' VAPS were observed by the anaesthetist at the time of referral for epidural analgesia. Because contractions may vary in strength, VAPS were obtained for each parturient as the mean of scores recorded for three consecutive uterine contractions. Each pain score was measured immediately after the corresponding uterine contraction and was referred to the pain of that contraction. Demographic data and obstetrical parameters were also studied.
For statistical analysis, parturients made up four groups corresponding to four periods of the day: night (from 1:01 a.m. to 7:00 a.m.), morning (from 7:01 a.m. to 1:00 p.m.), afternoon (from 1:01 p.m. to 7:00 p.m.) and evening (from 7:01 p.m. to 1:00 a.m.). In addition, VAPS were compared between daytime (7:01 a.m. to 7:00 p.m.) and nocturnal (7:01 p.m. to 7:00 a.m.) periods.
All variables were expressed as mean (SD). One-way analysis of variance followed by Bonferroni's correction was used for group comparisons. An unpaired t test was used for comparison of VAPS between daytime and nocturnal periods. With an SD of 18 and assuming =0.05, we calculated that at least 35 parturients per group were required to detect a difference of 20 in VAPS with a 99% power (ANOVA). P<0.05 indicated statistical significance.
Two hundred and twenty-two women were consecutively enrolled in the study. Parturients' characteristics and obstetrical data were comparable in all four study groups (Table 1). The mean VAPS were lower (P<0.0001) in the daytime period [75.6 (15.1)] compared with the nocturnal period [85.7 (14.1)]. Furthermore, when the four groups were compared, VAPS were lower in the morning compared with the other time groups (Table 1).
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Comment |
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In summary, the present study suggests that circadian variations may exist in labour pain perception, and this should be taken into account when enrolling parturients in comparative studies designed to assess or treat labour pain.
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Acknowledgments |
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References |
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