NICOM® is a recently developed noninvasive cardiac output monitoring device, and indices derived from NICOM® such as SVV has been reported to predict fluid responsiveness in the previous studies. However, its usefulness in prone positioning has not been investigated. Thus, the aim of this prospective observational study is to evaluate the usefulness of stroke volume variation (SVV) derived from NICOM® to predict fluid responsiveness in prone patients undergoing spine surgery.

Inclusion Criteria:

• ASA I or II patients undergoing spine surgery in prone position

Exclusion Criteria:

• Pre-existing arrhythmic disorders/moderate to severe valvular heart disease/obstructive pulmonary disease (COPD grade >2), left ventricular dysfunction with LV EF less than 50, preoperative need for inotropics or vasopressors
• BMI >30kg/m^2 or <15kg/m^2
• Preoperative serum Cr > 1.3mg/dL
• Patients with coagulopathy

Patients undergoing spine surgery under general anesthesia in prone position