Epidural pressures and spread of 2% lidocaine in the epidural space: Influence of volume and speed of injection of the local anesthetic solution

Background and Objectives. The impact of epidural pressures on the spread of epidural block is controversial. This study examined the effect of volume and speed of injection of local anesthetics on epidural pressures and the spread of anesthesia. Methods. Twenty women undergoing epidural anesthesia received a test dose of 3 mL of 2% lidocaine with epinephrine 1:200,000 over 6 seconds and subsequently the main dose of 15 mt of the solution over 30 seconds (group I) or 3 minutes (group II). Variables studied included epidural pressures and the extent and duration of thermal and sensory block. Results. Peak epidural pressure following the main dose was significantly higher in group I as compared to group II. All other epidural pressures and the extent and duration of sensory and thermal block were similar in both groups. The peak epidural pressure in group II and the pressures obtained at 3 minutes after the main dose in both groups were inversely correlated with the extent of the thermal block and directly correlated with its regression time. Conclusions. The peak epidural pressures correlated with the speed of injection of the lidocaine solution and not with its volume, whereas the remaining epidural pressures correlated with its volume and not with the speed of injection. The extent and duration of the thermal block exhibited a more consistent correlation (inverse and direct, respectively) with the epidural pressures than those of the sensory block.