EFFECTS OF EPINEPHRINE AND CLONIDINE ON PLASMA-CONCENTRATIONS OF SPINAL BUPIVACAINE

ASA II-III patients, scheduled for peripheral vascular surgery, were included in a study designed to assess the effect of spinal epinephrine and clonidine on plasma concentrations of spinally administered 0.5% glucose-free bupivacaine. Patients were allocated randomly to three groups to receive via a spinal catheter 22.5 mg (4.5 ml) of bupivacaine alone (Group B, 9 patients) or combined with 0.3 mg epinephrine (Group BE, 10 patients) or 0.15 mg clonidine (Group BC, 10 patients). Sensory blockade was assessed by pin-prick and motor blockade on the Bromage scale. Bupivacaine plasma concentrations were measured by gas chromatography. A trend to prolongation of local anaesthetic blockade was documented in patients receiving bupivacaine plus epinephrine or clonidine. (Time to regression of sensory blockade to L2: 170 +/- 75 min in Group B, 230 +/- 50 min in Group BE, 232 +/- 64 min in Group BC.) The maximum peak concentration (C(max)), the time to reach C(max) (T(max)) and the time-concentration curve from 0-180 min (AUC) were not different for the three groups (C(max) 228 +/- 112 ng . ml-1 in Group B, 215 +/- 103 ng . ml-1 in Group BE, 234 +/- 159 ng . ml-1 in Group BC; T(max) 41 +/- 34 min in Group B, 59 +/- 31 min in Group BE, 68 +/- 32 min in Group BC; AUC 31.0 +/- 1.7 mg . ml-1 . min-1 in Group B, 27.3 +/- 1.1 mg . ml-1 . min-1 in Group BE, 27.0 +/- 1.1 mg . ml-1 . min-1 in Group BC). The results of this study suggest that epinephrine and clonidine do not decrease blood resorption of spinal bupivacaine.