• Tao Xu, Jia Wang, Geng Wang, and Qing-Guo Yang.
• Department of Anesthesiology, Beijing Jishuitan Hospital Beijing 100035, China.
• Int J Clin Exp Med. 2015 Jan 1; 8 (6): 9603-6.

ObjectiveTo observe the potency ratio of hyperbaric to isobaric solutions of ropivacaine in subarachnoid block for knee arthroscopy.MethodsFifty patients receiving knee arthroscopy under combined spinal-epidural anesthesia were randomly divided into isobaric ropivacaine group and hyperbaric ropivacaine group (0.5% ropivacaine, prepared with equal volume of 10% glucose and 1% isobaric ropivacaine). Successful criteria of spinal anesthesia were (1) a bilateral loss of pinprick sensation at or above the level of T12; (2) adequate motor block during knee arthroscopy (modified Bromage's score ≥2); and (3) no requirement of additional epidural administration at least within 60 min after intrathecal injection. Drug consumption was determined with up-and-down method, and then ED50 was calculated.ResultsThe ED50 of isobaric ropivacaine was 9.71 mg (95% CI 8.11-11.32), and the ED50 of hyperbaric ropivacaine was 6.55 mg (95% CI 6.07-7.04), and the relative potency ratio was 0.67 (95% CI 0.56-0.80) for hyperbaric/isobaric ropivacaine.ConclusionsThe ED50 of hyperbaric ropivacaine is less than that of isobaric ropivacaine in subarachnoid block anesthesia for knee arthroscopy.

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