Determination of ketamine ED50 in pediatric anesthesia for MRI scanning with sequential method

Abstract

Objective To determine the median effective dose (ED50) of ketamine in pediatric anesthesia for magnetic resonance imaging (MRI) scanning with sequential method. Methods 34 children (ASA gradeⅠ-Ⅱ) scheduled receiving MRI scanning under ketamine anesthesia were chosen. The Ⅰ.M. dose was set as 6 mg/kg for the incipient child and the sequent dose for the next child was adjusted by increasing or decreasing 0.5 mg/kg using up-and-down sequential method, according to the response of previous child to the administered dose. Satisfactory anesthesia was defined as that scanning was successfully and uninterrupted completed with a single intramuscular injection of ketamine or otherwise as failure. In case of failure, a higher degree of dose was needed for the sequent child. The ED50 of ketamine was derived from the data obtained using weighted averaging method. Results The ED50 of ketamine is 7.058 mg/kg and the 95 % confidence interval is 6.833 6 mg/kg-7.289 8 mg/kg. Conclusion Using sequential method to determine ketamine ED50 is convenient and with high performance, and the result is creditable. Ketamine ED50 is useful to make pediatric anesthesia for MRI scanning more rapid and safer. Key words: ketamine; MRI ; sequential method; ED50