Use of ropivacaine 0.2% with or without clonidine 1 μg/kg for epidural labor analgesia

Madam,

I read with great interest the recent study by Kumari et al.[1]“Comparison of ropivacaine (0.2%) with or without clonidine 1 μg/kg for epidural labor analgesia: A randomized controlled study.” I sincerely appreciate the efforts taken by the authors in designing, conducting, and reporting their study. However, there seems to be a major flaw in the methodology of their study with respect to the preparation of study drugs. According to the authors, they had drawn 3 ml of 0.5% ropivacaine in a 10 ml syringe and added 7 ml of saline to obtain 10 ml of 0.2% ropivacaine solution for Group R patients. Similarly, for Group RC patients, the solution was prepared by adding 1 μg/kg of a 100 μg/ml solution of clonidine to 3 ml of 0.5% ropivacaine and injection normal saline q.s. 10 ml. So, in both the groups, the solution that they prepared, were in effect, 0.15% ropivacaine and not 0.2% ropivacaine, as claimed by them. Ideally, they should have taken 4 ml of 0.5% ropivacaine instead of 3 ml to get a final 10 ml of 0.2% solution of ropivacaine.

This article made an interesting read and illuminated us on a very important topic, however, because they had actually studied a different concentration of the drug in question, this might have a bearing on the interpretation of the study results.

The authors had concluded that the addition of clonidine 1 μg/kg to epidurally administered ropivacaine 0.2% improves the onset of analgesia, prolongs its duration, and is very well accepted by the parturients. Considering the fact that both 0.15% and 0.2% ropivacaine can be used for epidural labor analgesia (ELA)[2,3] in routine clinical practice, and that the same concentration of ropivacaine was used in both the groups, this conclusion may still hold true. However, I have some reservations about their additional conclusion regarding the incidence of undesirable motor blockade, cesarean section/instrumental vaginal delivery, or neonatal depression. I wonder if the incidences of undesirable motor blockade or neonatal depression would still have been the same (and more importantly, acceptable) had they actually added 1 μg/kg of clonidine to 10 ml of 0.2% ropivacaine (20 mg) rather than to 0.15% ropivacaine (15 mg). Muir et al.[3] had reported a 21% incidence of motor block using 10 ml of 0.25% ropivacaine (25 mg). Greater incidences of motor block have been reported by Eddleston et al.[4] (25–37.5 mg ropivacaine) and McCrae et al.[5] (50 mg ropivacaine), with figures as great as 65%. Authors of the present study have not mentioned the exact incidences of motor blockade in the two groups, they had only mentioned that the difference was not significant.

In conclusion, the authors actually compared ropivacaine (0.15%) with or without clonidine 1 μg/kg for ELA. Still they ended up concluding about ropivacaine 0.2% with or without clonidine 1 μg/kg for ELA, thus providing a false sense of assurance among practicing clinicians regarding the safety of use of clonidine (1 μg/kg) with 0.2% ropivacaine for ELA. Moreover, the relevant research question regarding the safety of adding clonidine 1 μg/kg to 0.2% ropivacaine for ELA with respect to undesirable motor blockade and neonatal depression still remains unanswered.

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