Fig. 1

The effects of tramadol or remifentanil dose on the incidence of postoperative shivering: (a) the low-dose remifentanil group (n = 31) included 16 who were treated with tramadol treatment [LT(+)] and 15 who were not [LT(−)] and (b) the high-dose remifentanil group (n = 32) included 17 treated with tramadol [HT(+)] and 15 who were not [HT(−)]; (c) the tramadol treatment group (n = 33) included 17 administered high-dose remifentanil and 16 who were administered low-dose remifentanil, while (d) the group not administered tramadol group (n = 30) included 15 who received high-dose remifentanil and 15 who received low-dose remifentanil. The white portion represents those patients who did not shiver postoperatively, and the black portion those who experienced postoperative shivering. Fisher’s exact test was used for statistical analyses