Ropivacaine is a long acting, amide-type local anesthetic with a chemical structure similar to that of bupivacaine. In this study we investigated the efficacies of 18 ml of 0.5% bupivacaine, and of 0.5% and 0.75% ropivacaine to provide caudal anesthesia.

Sixty ASA physical status 1 or 2 patients undergoing hemorrhoidectomy were randomly allocated to 3 parallel treatment groups to receive either 18 ml of 0.5% bupivacaine, or 0.5% or 0.75% ropivacaine. Caudal anesthesia was performed using the loss of resistance method via sacral hiatus. Soft touch testing around the anal sphincter muscle, the pin prick method at the S3 dermatome, onset time of loss of anal sphincter reflex, and sensory block were checked following local anesthetic injection. Duration of sensory block was assessed at 30 minute intervals through out block duration. Quality of muscle relaxation was assessed by the surgeon at the end of each operation. Blood pressures were measured and the incidences of nausea, vomiting and dizziness were recorded.

Significant differences were observed between the 0.5% ropivacaine and 0.75% ropivacaine groups (P < 0.05) with regard to onset time of loss of anal sphincter muscle reflex and sensory block. The 0.75% ropivacaine group showed a longer duration of analgesia. No significant differences were found between the 0.5% bupivacaine, or the 0.5% or 0.75% ropivacaine groups in terms of the onset time of loss of anal sphincter muscle reflex or sensory block, or the duration of analgesia. Quality of muscle relaxation was similar in the three groups.

In our study the 0.75% ropivacaine group showed rapid loss of anal sphincter tone, rapid onset of sensory block, and longer analgesia duration than the 0.5% ropivacaine group, and 0.75% ropivacaine was similar to 0.5% bupivacaine in these respects. These results suggest that 0.5% or 0.75% ropivacaine may be as useful as 0.5% bupivacaine in caudal anesthesia for hemorrhoidectomy.