ED 50 and ED 90 of intrathecal hyperbaric 2% prilocaine in ambulatory knee arthroscopy DE 50 et DE 90 de la prilocaine 2 % intrathecale hyperbare dans l'arthroscopie du genou en ambulatoire

AbstractPurpose Hyperbaric 2% prilocaine (HP) is increasinglyused for spinal anesthesia in day-case surgery. The aim ofthis prospective double-blind study was to determine theeffective dose (ED) 50 and the ED 90 of HP for patientsundergoing knee arthroscopy.Methods Doses of HP were determined using an up-and-down sequential allocation technique. Sequences wereanalyzed by isotonic regression analysis. A subsequentobservational study was performed with the calculatedED 90 in 50 patients to confirm the initial result and todescribe the induced blockade effects and side effects.Times corresponding to onset and duration of sensory andmotor block, surgical data, and side effects were recorded.Results The ED 50 was estimated at 28.9 mg (95%confidence interval [CI]: 26.5 to 35.3) and the ED 90 wasestimated to be 38.5 mg (95% CI: 35.7 to 39.5). A 40 mgdoseofHPprovidedefficientanesthesiain46patients(92%,95% CI: 82 to 98). The average (SD) time to effectiveanesthesia was 14.5 (3.9) min. Complete sensory block atlevel T12 was obtained after ten minutes in 44 of 50 patients.The average (SD) duration of the sensory block was 205(36.1) min. Maximal level of sensory block was obtained atthe T8-T11 levels in 41 of 50 patients without hemodynamicinstability. A Bromage 3 score was obtained in 40 of the 46patients who achieved successful anesthesia after 30 min.Patients did not experience urinary retention, nor were anysigns of transient neurologic symptoms observed.Conclusion ThisstudydeterminedtheED