Figure 4. Duration of postoperative analgesia provided by epidural clonidine as the sole analgesic agent in the different groups expressed as a survival curve. Patients in group 1 (n = 4) 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 = 14) received an initial dose of clonidine of 4 micro gram/kg in 10 ml saline given in 20 min and 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 = 19) received an initial dose of clonidine of 8 micro gram/kg in 10 ml saline given in 20 min and 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 represents the extubation. The durations of analgesia among the three groups are significantly different (P = 0.025 by Gehan's generalized Wilcoxon test). The duration of analgesia observed in group is significantly different from group 1 (P = 0.025) and group 2 (P = 0.04, by Cox's F test).