Minimum local analgesic concentration of ropivacaine for intra-operative caudal analgesia in pre-school and school age children - analysis using the Dixon method

Abstract

Deng et al. recently quantified the minimal local anaesthetic concentration of ropivacaine for intra-operative caudal analgesia in pre-school and school age children [1]. Although in their methods, the authors stated that the concentration of ropivacaine received by a particular subject was determined according to Dixon’s up and down method, the ED50 presented in the results was calculated using probit and logit regression only. We respectfully suggest that for proper analysis of the data, the ED50 with 95% CI should have been estimated from the up-down sequences using the method of Dixon and Massey. The sequences should then have been subjected to probit regression analysis as a backup or sensitivity test. We calculated the ED50 by averaging the midpoint concentration of all independent pairs of patients involving a crossover according to Dixon and Massey’s method [2, 3] using all 25 patients depicted in both groups. The ED50 (95% CI) values for school age and pre-school children are 0.143% (0.139–0.147) and 0.098% (0.093–0.103), respectively, compared with the authors’ results of 0.143% (95% CI: 0.132–0.157%) and 0.107% (95% CI: 0.089–0.122%). This would not have altered the overall result of the study, but is a more accurate presentation of their results. No external funding and no competing interests declared. Previously posted at the Anaesthesia Correspondence website: http://www.anaesthesiacorrespondence.com.