Single versus staged epidural injections of 0.75% bupivacaine: pharmacokinetic and pharmacodynamic effects

Epidural anesthesia may be performed as a single injection or by staged doses. Thirty patients undergoing primary total hip replacement were randomly assigned to have epidural anesthesia using a single injection or a staged technique with 25 mL of 0.75% bupivacaine. Arterial plasma bupivacaine concentrations were significantly higher in the single injection group for the first 15 min but were not significantly different thereafter. Peak bupivacaine concentrations did not differ significantly between groups, but the time to achieve the peak concentration was delayed by staging injections (P = 0.001). Hemodynamic effects were similar between groups. Resolution of thoracic sensory block through T12 and duration of motor block measured by Bromage scale were both significantly longer in the staged injection group (P < 0.01). The method of epidural injection may affect resolution of neural block and the time to reach peak arterial plasma concentration of local anesthetic.