Procedures
The dose of 2 mg/kg of the bodyweight of methylene blue (20 mg/2 ml) (Jichuan Medicine Co., Ltd, Taixing, China) was diluted with saline solution to be 50 ml; the placebo was 50 ml of saline solution. Both were prepared by a medical staff who did not participate in the rest study. Before general anesthesia induction, all patients received placement of a central venous catheter (B. Braun, Melsongen, Germany) and Swan-Ganz catheter via the right jugular vein, and an arterial catheter (18G) at the site of the left radial artery under local anesthesia. Invasive arterial blood pressure (ABP) and central venous pressure (CVP) were monitored continuously during operation. The surgical procedures were well matched between the two groups.The methylene blue solution or normal saline was administrated by a continuous intravenous infusion at a rate of 2.5 ml/min before anesthesia induction, and then all the patients were induced with the administration of midazolam (0.02–0.05 mg/kg), sufentanil (0.5–1 μg/kg), etomidate (0.2–0.3 mg/kg), and cisatracurium (0.2–0.3 mg/kg). The patients received trachea intubation and ventilated with 8–10 ml/kg of tidal volume, 12–16 rpm, 1:2 of I:E to maintain EBiochemical indexes of kidney and liver function