Objective To compare the plasma volume expanding effect of hydroxyethyl starch (HES)130/0.4 and electrolyte solution (E-HES) and HES 130/0.4 and normal saline (NS-HES) in patients undergoing noncardiac surgery under general anesthesia.Methods A multicenter,prospective,randomized,double-blind,controlled clinical trial was conducted.Two hundred and forty-two ASA Ⅰ or Ⅱ patients aged 18-64 yr with body mass index 18-29 kg/m2 undergoing noncardiac surgery were randomly divided into 2 groups: group E-HES and group NS-HES.E-HES and NS-HES 15 ml/kg was infused iv over 1 h immediately after induction of anesthesia in groups E-HES and NS-HES respectively.Arterial blood samples were taken before (baseline) and at 15 min after the end of HES infusion for blood gas analysis (pH value,BE,HCO3-,K+,Na+,Cl-,Mg2+ ) and measurement of Hb,Hct,blood chemistry (ALT,AST,Cr,BUN,Glu) and coagulation function.The electrolyte abnormality,requirement for vasopressor,treatment-related adverse effects (prolonged prothrombin time,activated partial thromboplastin time and hyperchloremia) and fluid balance were recorded.Results Of the 242 patients,122received E-HES and 120 received NS-HES.Ninety-one patients in group E-HES and 95 in group NS-HES completed the trial.The pH value,BE,HCO3 -,K+,and Mg2+ were significantly higher and Na+ and Cl- lower at 15 min after HES infusion was finished in group E-HES than in group NS-HES.BE,HCO3-,Na+,Mg2+,Hb and Hct were significantly decreased while Cl- was significantly increased in group NS-HES while Na+,Mg2+,Hb and Hct were significantly decreased and Cl- was increased in group E-HES at 15 min after HES infusion as compared with the baseline values before infusion.The incidence of clinical significant abnormality in plasma K+ and Cl- was significantly lower in group E-HES than in group NS-HES.There were no significant differences in Hb,Hct,urine output,amount of HES infused,vasopressor requirement,the incidence of clinically significant abnormality in blood chemistry and treatment-related adverse effects between the 2 groups.Conclusion E-HES and NS-HES have the same plasma volume expanding effect,but E-HES maintains better electrolyte and acid-base balance than NS-HES.