Fig. 4. Time course of propofol target blood concentration for maintenance. Data are mean ± SD. *P < 0.0001 versus  Group S. †P < 0.05 versus  Group R^0.25. R^0.25= 0.25% ropivacaine; R^0.50= 0.50% ropivacaine; R^0.75= 0.75% ropivacaine; S = saline; T1 = two-lung ventilation in the lateral decubitus position; T2 = one-lung ventilation after 10 min; T3 = one-lung ventilation after 20 min; T4 = at the end of surgery with two-lung ventilation.