Figure 1. Efficacy of the anesthesia provided by the different epidural clonidine solutions assessed by the intravenous bolus of sufentanil required to blunt the episodes of tachycardia and hypertension occurring with surgical stimulation. Patients in group 1 (n = 10) received an initial dose of clonidine of 2 micro gram/kg in 10 ml saline given in 20 min and followed immediately by an infusion of 0.5 micro gram [center dot] kg (-1)[center dot] h-1(5 ml/h); patients in group 2 (n = 20) received an initial dose of clonidine of 4 micro gram/kg in 10 ml saline given in 20 rain followed by an infusion of 1 micro gram [center dot] kg-1[center dot] h-1(5 ml/h); and patients in group 3 (n = 20) received an initial dose of clonidine of 8 micro gram/kg in 10 ml saline given in 20 min followed by an infusion of 2 micro gram [center dot] kg-1[center dot] h (-1)(5 ml/h). The data are presented as survival proportions. Time 0 represent the induction of anesthesia. The three groups are significantly different (P = 0.003 by Gehan's generalized Wilcoxon test). The duration of analgesia observed in Group 3 is significantly different from groups 1 and 2 (P < 0.05).