[Dose-response relationship of clonidine with epidural administration of ropivacaine in orthopedic procedures of the lower extremities].

OBJECTIVE

The aim of this study was to investigate preliminarydose-range effects of clonidine added to ropivacaine for epidural analgesia in elective orthopedic surgery of the lower limbs with doses, causing a minimum of cardiovascular side effects.

METHODS

60 patients were randomly assigned to receive in a double-blind fashion a mixture of 1 mg/cm height ropivacaine plus saline or 1 mg/cm ropivacaine plus 25 micrograms, 50 micrograms, 75 micrograms, 100 micrograms or 150 micrograms clonidine for epidural analgesia. The sensory and motor function were determined at defined time intervals for 30 minutes. Heart rate and blood pressure were controlled and sedation score was judged. The postoperative 2-segment-regression of pin-prick and the onset of pain were recorded.

RESULTS

The six groups were comparable in demographic data and in term of onset time. The prolongation of analgesia reached 513 +/- 92 min (p = 0.002) for 150 micrograms clonidine, 460 +/- 148 min (p = 0.073) for 100 micrograms clonidine, 440 +/- 86 min (p = 0.057) for 75 micrograms clonidine compared with 347 +/- 114 min for saline. In an equal manner, 2-segment-regression for pin-prick was extended to 251 +/- 47 min (p = 0.018) for 150 micrograms clonidine, 238 +/- 33 min (p = 0.034) for 100 micrograms clonidine, 229 +/- 29 min (p = 0.027) for 75 micrograms clonidine and 178 +/- 43 min for saline. Heart rate dropped down in all groups. Mean arterial pressure decreased significantly in the groups with 75, 100 and 150 micrograms clonidine. Sedation score increased continuously from 0.6 +/- 0.5 (saline) to 1.8 +/- 0.8 (150 micrograms clonidine).

CONCLUSION

We conclude that 150 micrograms clonidine significantly enhances the duration of analgesia of epidurally administered ropivacaine in a mean of 171 mg. This time interval is longer than the one with 200 mg ropivacaine alone. But, there are side effects in form of decrease of arterial pressure. Cardiovascular monitoring seems to be essential. Because of the enhanced analgesia duration, the time interval for reloading epidural anaesthesia are increased.