In this group,an arterial catheter was inserted preoperatively. An indwelling radial artery catheter was connected to the hemodynamic monitoring system (EV1000; Edward Lifesciences Corp., Irvine, CA, USA) via FloTrac™ (Edwards Lifesciences Corp.) sensors.

In this group,haemodynamic parameters were collected simultaneously by the thoracic bioimpedance (BioZ.com™) monitoring.

Haemodynamic parameters were collected simultaneously by the Flotrac monitoring.

After anesthesia induction, volume loading was initiated. For each volume loading step (VLS), 100 mL of colloid solution (6% hydroxyethyl starch) was administered over a 2-minute duration. The SVV was measured and recorded simultaneously by FloTrac (SVV-FloTrac) and Transthoracic electrical bioimpedance(SVV-BioZ). Volume loading steps (VLS) continued until no responsive VLS was observed. Responsive VLS, defined as an increase in Flotrac-SV by at least 5%, and nonresponsive VLS, characterized by no change or an increase in Flotrac-SV by less than 5%, were subsequently identified. Multiple analysis methods were used to determine the agreement of the two SVVs.

After anesthesia induction, volume loading was initiated. For each volume loading step (VLS), 100 mL of colloid solution (6% hydroxyethyl starch) was administered over a 2-minute duration. The SVV was measured and recorded simultaneously by FloTrac (SVV-FloTrac) and Transthoracic electrical bioimpedance(SVV-BioZ). Volume loading steps (VLS) continued until no responsive VLS was observed. Responsive VLS, defined as an increase in Flotrac-SV by at least 5%, and nonresponsive VLS, characterized by no change or an increase in Flotrac-SV by less than 5%, were subsequently identified. Multiple analysis methods were used to determine the capacity to predict the fluid responsiveness of these two devices.