Mean VAS pain scores; rest VAS, pain scores at rest; effortVAS, pain scores during deep breathing. The error bars indicate 1 sd. Group S, control group; Group M, magnesium group. *P<0.05 vs Group S; ^†P<0.05 compared with baseline (immediate postoperative) value in Group S; ^‡P<0.05 compared with baseline (immediate postoperative) value in Group M.