BACKGROUND: We studied hemodynamic changes using a noninvasive partial CO2 rebreathing cardiac output method (NICO) and esophageal Doppler monitor (EDM), and metabolic changes in elderly patients undergoing bilateral total knee replacement arthroplasty (BTKA). METHODS: Twenty patients undergoing BTKA were studied. Hemodynamic and metabolic parameters were measured before tourniquet inflation (TI), 0, 3, 6, 9, 15, 30, 45 min after TI, and 0, 3, 6, 9, 15, 30 min after tourniquet deflation (TD) and skin suture. Stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) were measured using NICO and EDM. RESULTS: Mean blood pressure (MBP), central venous pressure (CVP), and SVR had significant increases in TI, and decreases in TD compared with value measured before TI (baseline value). Especially, MBP had higher decrease in the second tourniquet compared with first tourniquet, SV and CO were decreased in TI, and increased in TD compared with baseline value, HR had significant increases in the TD of second tourniquet. pH and lactate were shown significantly lower values at the second tourniquet compared with the first tourniquet (P < 0.05). The bias and precision derived from CO between EDM and NICO was 0.27 +/- 0.41 L/min, and CO by NICO was smaller than that by EDM. The correlation coefficient between NICO and EDM was calculated to be 0.43. CONCLUSIONS: MBP, SV, CO, pH and lactate were shown to be higher in the second tourniquet in BTKA. NICO showed lower CO compared with EDM after TD in patients undergoing BTKA, but statistically insignificant at most measurement.