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Description / Table of Contents: Abstract Several clinical studies have demonstrated the efficacy of ropivacaine in different regional anaesthesia techniques, e.g., epidural anaesthesia. However, the efficacy of ropivacaine for spinal anaesthesia has only been demonstrated in animal experiments up to now. The objective of this study was the investigation of the efficacy and appropriate dosage of isobaric ropivacaine for spinal anaesthesia in humans. Methods. In a randomised, double-blind study, spinal anaesthesia with ropivacaine was performed in two groups of 20 patients each (group I: ropivacaine 0.5%, 3 ml=15 mg; group II: ropivacaine 0.75%, 3 ml=22.5 mg). Spinal anaesthesia was performed with a 25 G needle in the midline at the L3–4 level with the patient sitting up, preceded by local infiltration of 2 ml mepivacaine 0.5%. Spread and regression of sensory block were assessed by testing loss of sensation to cold. Development of motor block was concurrently recorded by means of a modified Bromage scale (motor block was assessed in the hip, knee and ankle joints and recorded as complete or incomplete according to degree). The findings are presented as mean values. Results. Onset of analgesia to L5 and S1 was 2 min in both groups, and to T12 and T10 8 and 12.5 min, respectively, in group I and 12.5 and 13 min, respectively, in group II; these differences were not statistically significant. Mean maximum spread was to T10 in group I and T8 in group II. Onset of maximum cranial spread was 24 min in group I and 32 min in group II. Duration of analgesia in the segments relevant to the performed operations varied in group I between 1.5 and 5.7 h (S3 4.9, S1 5.7, L4 5.4, L2 3.0, T12 2.0, T10 1.6, T8 1.5 h) and in group II between 1.8 and 5.9 h (S3 5.4, S1 5.9, L4 5.7, L2 4.1, T12 2.9, T10 2.3, T8 1.8 h). These differences were significant in the segments S3, L3, L2, L1, T12, and T10. In 5 patients (20%) in group I adequate analgesia for the planned surgical intervention was not obtained. In 4 of these 5 patients the required spread of the spinal block was not reached; in 2 general anaesthesia had to be performed and in 2 the required analgesia could be obtained by administration of an analgesic (fentanyl). In the 5th patient the level of spinal block was sufficient for the planned operation, however, the quality of analgesia was not, i.e., additional analgesics were required. In the group that received the 0.75% solution additive analgesics were necessary in 1 patient (5%) because a sufficient level of anaesthesia for the planned operation was not obtained. In group I all patients had a complete motor block in all three joints (hip, knee, and ankle); in group II, however, the motor block was incomplete in 6 patients. This difference between the 2 groups was statistically significant. Onset of motor block of hip, knee, and ankle joints occurred after 10, 15, and 15 min, respectively, in group I and 10, 12, and 15 min, respectively, in group II. These differences were not statistically significant. Duration of motor block in the three joints was significantly longer (3.4, 2.8, and 3.8 h)in group II than in group I (2.4, 1.9, 2.7 h). Statistically significant changes in systolic and diastolic blood pressures (BP) and heart rate (HR) were recorded in both groups in the course of the study period. Relative BP changes were assessed in the individual patients. There were no statistically significant changes between the two groups with regard to relative changes in systolic and diastolic BP and HR. Bradycardia occurred a total of 13 times in 10 patients in group I and in 11 patients in group II. A BP decrease of 〉20% was measured in 1 patient in each group. Twelve of the 40 patients complained a headache in the first 6 days; in this respect the groups did not differ significantly. There was no difference between male and female patients with regard to side effect profile. Conclusion. At concentrations of 0.5% and 0.75%, ropivacaine results in long-lasting spinal anaesthesia. Duration of analgesia as well as duration and degree of motor block increase with the higher concentration. Neurotoxic effects of the local anaesthetic were not observed. A dose of 3 ml ropivacaine 0.75% seemed to be suitable for the gynaecologic and urologic operations (Table 3) with regard to efficacy of analgesia and local anaesthetic spread.