Objective To investigate the efect of controlled hypotension with remifentanil and the diversity of renin-angiotensin-aldosterone system in total hip arthroplasty.Methods Forty-five patients undergoing elective total hip arthroplasty,with ASAI~Ⅱ,were equally randomized into three groups,:Group R,remifentanil-induced hypotension.Group N,sodium nitroprusside-induced hypotension.Group C,remifentanil-maintained normal arterial tension.Adjust remifentanil and sodium nitroprusside infusion rate for controlled hyp...