The Effect of High vs. Low Fluid Volume on Ocular Parameters in Prone Spine Surgery

In the prone position, the intraocular pressure and optic nerve sheath diameter increase progressively with time as compared with those in the supine position. Excessive fluid infusion may further increase intraocular pressure and optic nerve sheath diameter. Pulse pressure variation (PPV) is a dynamic index which can effectively assess fluid responsiveness during general anesthesia.Therefore,the investigators have designed a study to compare the effect of different fluid volume infusion guided by low and high PPV indices on intraocular pressure and optic nerve sheath of patients undergoing prone spine surgery with general anesthesia. One group of the patients will receive relatively loose fluid infusion (target value of PPV: 6%-9%),while the other group of the patients will receive limited fluid infusion (target value of PPV: 13%-16%).

Inclusion criteria

• Scheduled for elective spine surgery in prone position under general anesthesia
• American Society of Anesthesiologists (ASA) physical status I or II
• Have signed consent form

Exclusion criteria

• History of eye disease or eye surgery
• Pregnancy or breast feeding
• Known Allergy to latex or Ringer's lactate solution
• Hyperlactacidemia，uncontrolled hypertension, diabetes mellitus, arrhythmia, cardiovascular disease，chronic pulmonary disease, swelling of any body part, abnormal of liver or renal function, anemia, etc.
• Body mass index（BMI）>30
• Expected operation time >6 hours
• Estimated Intraoperative hemorrhage >1000ml
• Taking part in other clinical trials in the last 3 months or at present