COMPARISON OF CLONIDINE AND EPINEPHRINE IN LIDOCAINE FOR CERVICAL PLEXUS BLOCK

Background and Objectives. Carotid endarterectomy under cervical plexu s block offers the advantage of awake neurologic assessment. The hypot hesis was tested that the addition of clonidine 5 mu g/mL to lidocaine 1.5% for the block is as effective clinically; as the addition of epi nephrine 5 mu g/mL but without the associated tachycardia. Methods. In a double-blind, randomized, prospective trial of 40 patients, local a nesthetic. solutions of lidocaine 1.5% containing either clonidine 5 m u g/mL or epinephrine 5 mu g/mL were compared for cervical plexus bloc k in patients undergoing carotid endarterectomy. Each solution was adm inistered to 20 patients with a total lidocaine dose of 7 mg/kg. The e lectrocardiogram, heart rate, and arterial pressure (radial artery cat heter) were continuously monitored. Blood samples were drawn for deter mination of serum lidocaine levels during the first hour. Results. The block onset time (8.4 +/- 0.6 minutes for epinephrine, 8.8 +/- 0.8 mi nutes for clonidine) and duration (139 +/- 6.7 minutes for epinephrine , 148 +/- 5.8 minutes for clonidine) were not different between the tw o groups. During the period from completion of the block until incisio n there was a significant heart rate increase in the epinephrine group (23% mean rise) as compared with the clonidine group (4% mean rise) ( P < .003). There was no difference in blood pressure between the two g roups. The maximum plasma concentrations of lidocaine were 2.5-7.6 mu g/mL (mean, 4.5 +/- 0.3 mu g/mL) for the epinephrine group and 4.7-18. 4 mu g/mL (mean, 7.5 +/- 0.7 mu g/mL) for the clonidine group (P < .00 02). The maximum concentrations were reached 0-30 minutes (mean, 8 +/- 1.4 minutes) after injection for the epinephrine group and 0-10 minut es (mean, 4.5 +/- 7.1 minutes) for the clonidine group (P < .03). Conc lusions. Clonidine 5 mu g/mL is a useful additive to lidocaine 1.5% fo r cervical plexus block to reduce the incidence of tachycardia; howeve r omission of epinephrine results in higher serum lidocaine levels.