Effect of age on extradural dose requirement in thoracic extradural anaesthesia

We have investigated the effect of age on thoracic extradural dose requirements in 62 patients aged 20-79 yr. Fifteen millilitre of 2% mepivacaine was administered at a constant rate (1 ml s-1) by syringe pump through an extradural needle at the T9-10 interspace. A mean of 15.5 (SD 4.2) spinal segments were blocked 15 min after completion of the administration. The extradural dose requirement decreased with increasing age (r = -0.7, P < 0.001), the requirement in the elderly (60-79 yr) being about 40% smaller than that in young adults (20-39 yr).