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OBSTETRIC ANESTHESIA

The Effect of Clonidine on the Minimum Local Analgesic Concentration of Epidural Ropivacaine During Labor

Département d’Anesthésie-Réanimation Chirurgicale, Hôpital TENON, Assistance Publique Hôpitaux de Paris, Paris, France

Address correspondence and reprint requests to Francis Bonnet, Département d’Anesthésie-Réanimation Chirurgicale, Hôpital TENON, Assistance Publique Hôpitaux de Paris, 4 Rue de la Chine, 75020 Paris, France. Address e-mail to francis.bonnet{at}tnn.ap-hop-paris.fr

On the basis of the determination of minimum local analgesic concentration (MLAC), ropivacaine has been demonstrated to be less potent than bupivacaine during the first stage of labor. In this study we assessed the effect of clonidine on the MLAC of ropivacaine. Seventy-seven parturients of mixed parity requesting epidural analgesia for labor (cervical dilation, 3–7 cm) were included in the study. They received an epidural bolus of either ropivacaine (n = 30), ropivacaine plus clonidine 30 µg (n = 28), or ropivacaine plus clonidine 60 µg (n = 19) in the second part of the study. The concentration of the ropivacaine solution was determined by the response of the previous parturient in that group by using an up-down sequential allocation. A visual analog pain score of 10 mm within 30 min after the epidural bolus (20 mL) was considered an effective response. An effective result directed a 0.01% wt/vol decrement for the next patient. An ineffective result directed a 0.01% wt/vol increment. The MLAC of ropivacaine was 0.097% wt/vol (95% confidence interval, 0.085%–0.108%). It was unaffected by a 30-µg dose of epidural clonidine (0.081% [0.045%–0.117%]) but was significantly decreased by a 60-µg clonidine dose (0.035% [0.024%–0.046%]) (P < 0.001). This study documents a decrease in the MLAC of ropivacaine by clonidine, significant for a 60-µg dose.

IMPLICATIONS: Epidural ropivacaine potency in labor can be increased by the addition of epidural clonidine. This study demonstrates that 60 µg of epidural clonidine significantly decreases the minimum local analgesic concentration of ropivacaine during the first stage of labor but is associated with sedation.

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