Abstract: AIM: To observe dose-effect relationship of spinal anesthesia with 0.75% ropivacaine in caesarean section.METHODS: According to the dosage of 0.75% ropivacaine, 120 full-term and singlebirth puerperants were randomly divided into four groups of 30 people each.The dosage of group Ⅰ, Ⅱ, Ⅲ and Ⅳ were 1.5, 1.8, 2.1 and 2.4 mL respectively.The sensory and motor block of each group within 30 minutes after the injection were observed, and the hemodynamic changes and adverse effects were recorded.RESULTS: (1) Within 30minutes after the injection, the intermediate zone of pain disappeared highest block level of group I-IV were T₁₀, T₈, T₆ and T₅ respectively. (2) During the period of the first 30 minutes, there were 3 cases in group Ⅲ (10%) and 8 cases in group Ⅳ (27%) appeared chest distress and dyspnea, and the blood pressure of 5 cases in group Ⅲ (17%) and 12 cases in group Ⅳ (40%) dropped to 90 mm Hg (1 mm Hg=0.133 kPa).There were significant difference compared with group IV (P<0.05). (3) The cases (rate) of motor block of extremities inferior were 3 (10%), 6 (20%), 10 (33%) and 18 (60%) in the four groups respectively.Except that there was no significant difference between I, II, III groups (P>0.05), there were significant difference between group IV and other groups (P<0.05). (4) 4 cases in group Ⅲ (13%) and 10 cases in group Ⅳ (33%) appeared supine hypotensive syndrome, 4 cases in group Ⅲ (13%) and 12 in group Ⅳ (40%) appeared bradycardia. (5) 8 cases in group Ⅰ and 3 in group Ⅱ appeared pain during surgical incision, but group Ⅲ and Ⅳ showed excellent anesthetic effect and muscle relaxation.CONCLUSION: The dose-effect relationship of spinal anesthesia with 0.75% ropivacaine in caesarean section displayed that the dosage of 1.8～2.1 mL was safe and feasible.

Key words: ropivacaine, caesareansection, subarachnoidblock, dose-effectrelationship