Figure 2. Duration of postoperative analgesia provided by the different epidural solutions. Group 1 = epidural clonidine; group 2 = epidural bupivacaine, 0.5–0.25%; group 3 = epidural bupivacaine, 0.25–0.125%. The data are presented as survival proportions. Time 0 represents the extubation. The duration of analgesia among the three groups is significantly different (P < 0.05, Kaplan-Meier product-limit method). The duration of analgesia observed in group 1 was significantly different from groups 2 and 3 (P < 0.05, Cox F test).