Objective To observe the effects of acute normovolemic hemodilution(ANH)on target-controlled infusion(TCI)of etomidate blood drug concentration and adrenal cortical function.Methods Sixty patients who undergo elective multisegmental spine surgery,35 males and 25 females,aged 30-60 years,BMI 20-25 kg/m2,ASA physical status Ⅰ or Ⅱ,were divided into two groups using random number table method:ANH group and control group,30 patients in each group.Both groups used a target-controlled infusion of etomidate for anesthesia induction and anesthesia maintenance.In the ANH group,ANH was performed after steady anesthesia induction,ideal Hct 28％to 30％,and transfused within 1 hour after surgery;the control group was routinely treated.The dosage of etomidate was recorded.Liquid chroma-tography-tandem mass spectrometry(LC-MS/MS)was used to detect etomidate blood concentrations at the immediate postoperative,10,20,and 30 minutes postoperative periods in the two groups,and the immedi-ate moment autologous blood collected into the storage bag,preserved in the storage bag for 1 hour,and the immediate moment transfused back in the ANH group.Plasma concentrations of cortisol(Cor),adrenocorti-cotropic hormone(ACTH),and aldosterone(ALD)were measured by chemiluminescence immunoassay(CLIA)before the induction of anesthesia,immediately after the operation,and at 1 day and 2 days postop-eratively.Results There was no significant difference in the total dosage of etomidate between the two groups.Compared with the immediate postoperative period,the plasma etomidate concentration was signifi-cantly decreased 10,20,and 30 minutes after surgery(P<0.05).Compared with the control group,the concentration increased significantly 10 minutes after surgery in the ANH group(P<0.05).The plasma concentrations of etomidate were(547.8±119.4)ng/ml at the immediate moment autologous blood collected into the storage bag,(536.7±107.8)ng/ml at the preserved in the storage bag for 1 hour,and(522.8±91.7)ng/ml at theimmediatemoment transfusedbackinthe ANHgroup.Comparedwithbeforein-duction of anesthesia,the concentration of Cor and ALD immediately after the operation decreased signifi-cantly(P<0.05)and the concentration of ACTH was significantly higher(P<0.05).There were no sta-tistically significant differences in the concentrations of Cor,ALD,and ACTH between the two groups before induction of anesthesia 1 day and 2 days postoperatively.Conclusion In the orthopedic surgery of TCI eto-midate,return transfusion of collected autologous blood transiently(about 10 minutes)increases etomidate blood concentrations,the function of adrenal cortical will recover to the preoperative level within 24 hours after the operation.