Effect of dexmedetomidine on the medium effective concentration of ropivacaine for thoracic paravertebral block in aged patients

Objective To investigate effect of dexmedetomidine(Dex) on the medium effective concentration(EC50) of ropivacaine for ultrasound-guided thoracic paravertebral block. Methods Sixty ASA Ⅱor Ⅲ patients, aged 65-79 y, scheduled for lobectomy under video-assisted thoracoscopic surgery, requiring ultrasound-guided thoracic paravertebral block, were randomly assigned into 2 groups(n=30): control group(group C) and Dex group(group D). Paravertebral block was performed by using only ropivacaine in group C. In group D the mixture of ropivacaine and 0.75 μg/kg Dex was injected for the block. The initial concentration of ropivacaine was 0.5% and the ratio between the two successive concentrations was 1.2. If the block was effective, the next patient received a lower dose of ropivacaine, or if ineffective, a higher dose was given to the next patient. The EC50 and 95% confidence interval (CI) of ropivacaine were determined by using probit regression method. Results The EC50 of ropivacaine was 0.42% and 95%CI was 0.40%-0.45% in group C, The EC50 of ropivacaine was 0.35% and 95% CI was 0.32%-0.37% in group D. Conclusions The combined use of Dex can decrease the EC50 of ropivacaine for ultrasound-guided thoracic paravertebral block. Key words: Elderly; Dexmedetomidine; Paravertebral block