SINGLE VERSUS STAGED EPIDURAL INJECTIONS OF 0.75-PERCENT BUPIVACAINE - PHARMACOKINETIC AND PHARMACODYNAMIC EFFECTS

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