Appropriate fluid management is an important part of anesthesia in patients undergoing surgery, and several dynamic indices have been suggested to have high predictability for fluid responsiveness in patients receiving mechanical ventilation. Among various surgical positions, the prone position is known to cause unique physiologic and hemodynamic changes and affect the predictability and cut-off values of dynamic indices for fluid responsiveness. A previous study reported that pulse pressure variation (PPV) and corrected flow time were able to predict fluid responsiveness with relatively high accuracy in patients undergoing spine surgery in the prone position using a Wilson frame. However, the Jackson frame is known to have less effects on the cardiovascular system compared to the Wilson frame, and therefore may be physiologically more appropriate in patients undergoing surgery in the prone position. The pleth variability index (PVI) is a dynamic index that can be monitored non-invasively in patients under mechanical ventilation. The present study aims evaluate the validity of PPV and pleth variability index (PVI) as predictors of fluid responsiveness in the supine and prone positions in patients undergoing posterior lumbar spinal fusion using the Jackson table.

Inclusion Criteria:

1. Patients between the age of 19 and 75, scheduled for spine surgery under general anesthesia using the Jackson table

Exclusion Criteria:

1. Patient refusal
2. Patients that are not normal sinus rhythm on preoperative ECG
3. Patients with moderate~severe cardiac valve disease
4. Patients with an ejection fraction under 50%
5. Significant lung disease
6. Obesity (BMI>35kg/m2)
7. Patients with contraindications to esophageal doppler probe insertion
8. Illiterate patients or foreigners