Clinical Evaluation of Clonidine Added to Lidocaine Solution for Epidural Anesthesia

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Abstract
The effects of clonidine added to lidocaine solution used for epidural anesthesia were assessed in 92 women scheduled for surgery and premedicated with diazepam 10 mg po. Patients received 18 ml 2% lidocaine with clonidine 5 .mu.g .cntdot. ml-1 (group C-5, n = 26), with clonidine 10 .mu.g .cntdot. ml-1 (group C-10, n = 20), with epinephrine 5 .mu.g .cntdot. ml-1 (group E, n = 26), or plain (group P, n = 10). No significant difference in the number of segments of analgesia was found at any observation period among the four groups of patients. The decreases in mean blood pressure (BP) observed 20 min after epidural injection in those give clonidine (5 .+-. 8% for C-5, 10 .+-. 11% for C-10, mean .+-. SD) were similar to those given plain lidocaine 7 .+-. 12%) but significantly less than those given epinephrine (18 .+-. 12%, P < 0.01 vs. C-5 or P). The response of BP to ephedrine given for restoring BP during anesthesia was not attenuated in patients who received ephedrine clonidine,(18 .+-. 11% for C-10, mean .+-. SD) were similar to those given plain lidocaine (7 .+-. 12%) ephedrine given for restoring BP during anesthesia was not attenuated in patients who received epidural clonidine. Heart rate (HR) decreased significantly in patients given clonidine 10 .mu.g .cntdot. ml-1 (7 .+-. 8%, P < 0.01), but not in those given clonidine 5 .mu.g .cntdot. ml-1, whereas increased significantly in those given lidocaine plain or with epinephrine (10 .+-. 8% and 28 .+-. 14%, respectively), P < 0.01). The incidence of sinus bradycardia was similar among the four groups of patients. Significant differences were also observed in sedation score between clonidine groups and groups P or E; sedation appeared approximately 10-20 min after epidural in both clonidine groups. Although respiratory rate, PaO2, and PaCO2 did not change after epidural injection in both clonidine groups, PaO2 increased significantly (P < 0.01) in those given lidocaine plain or with epinephrine. Maximal plasma lidocaine concentrations (10-15 min after epidural injection) in group C-5 (n = 7,3.4 .+-. 0.2 .mu.g .cntdot. ml-1) and in group C-10 (n = 7, 3.6- .+-. 1.0 .mu.g .cntdot. ml-1) but were comparable to those in group P (n = 7, 2.9 .+-. 1.0 .mu.g .cntdot. ml-1) but were significantly greater (P < 0.05) than those in group E (n = 7), 2.3 .+-. 0.4 .mu.g .cntdot. ml-1). These results indicate that the addition of clonidine to lidocaine for epidural anesthesia provides a sedative effect and relatively stable hemodynamics, and that clonidine in a concentration of 1:200,000 or 1:100,000, in contrast to 1:200,000 epinephrine, tends to increase rather than to suppress the plasma lidocaine concentrations. The latter effect may be related to altered metabolism of lidocaine by clonidine.