Relative potency ratio between hyperbaric and isobaric solutions of ropivacaine in subarachnoid block for knee arthroscopy

摘要

Objective: To observe the potency ratio of hyperbaric to isobaric solutions of ropivacaine in subarachnoid block for knee arthroscopy. Methods: Fifty 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. Results: The 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. Conclusions: The ED50 of hyperbaric ropivacaine is less than that of isobaric ropivacaine in subarachnoid block anesthesia for knee arthroscopy.