The aim of this study is to examine the effects of intraoperative systemic use of dexmedetomidine on the intraocular pressure (IOP) in patients undergoing spine surgeries in a prone position under general anesthesia.

The study is a Prospective, Randomized, Placebo -controlled, Double-Blinded clinical trial Adult patients with an ASA physical status of class I, II or III who are scheduled for an elective spine surgery in prone position under general anesthesia will be included in the study.

The patients will be randomized with closed envelope manner into two groups: the group of dexmedetomidine and the group of normal saline.

In the dexmedetomidine group (DEX group), bolus dose 1,0 μg/kg of dexmedetomidine will be administered in 10min before induction to anesthesia and 0,4-0,8 μg/kg/h of dexmedetomidine will be infused continuously until the end of the surgery.

In the saline group (placebo group), the same volume of saline will be administered in an identical way.

All study medication will be prepared by an independent anesthesiologist who is not associated in the study (who will hold the randomization codes until the end of the study).

All patients will receive the same type of anaesthesia (TIVA with propofol) and postoperative analgesia including paracetamol 1gr iv (4 times/day) and continuous wound infiltration with ropivacaine 0.2% 5ml/h for 48 postoperative hours.

Basic monitoring for the study includes:

ECG, Invasive and noninvasive blood pressure, Heart Rate, EtCO2, SpO2, Cardiac Output (CO), Stroke Volume (SV), Stroke Volume Variation (SVV), Patient State index (PSi), IOP, Urine output.

Measurements

The measurement of IOP will be conducted in both eyes with Icare PRO tonometer by an ophthalmologist who will not know in which group the patient is in the below predefined time points:

• T1: before administration of the study drug
• T2: after administration of the bolus dose of the study drug
• T3: after tracheal intubation
• T4: just before prone position
• T5: just after prone position
• T6: 30min after T5
• T7: 60min after T6
• T8: 120min after T7
• T9: 180min after T8
• T10: at the end of the surgery and the patient in supine position At the time of each tonometer reading the following data set is collected: MAP, heart rate, EtCO2, SpO2, CO, SV, SVV, urine output, Psi, IOP. Moreover OPP will be calculated as MAP minus IOP.

Inclusion Criteria:

• Adult patients undergoing scheduled spine surgery performed in prone position under general anaesthesia

Exclusion Criteria:

• Patients who refuse to be a part of the study
• Patients with previous eye surgery
• Preexisting eye disease (e.g glaucoma)
• Allergy to the study drug or any drug which is in the trial
• Preoperative unstable hemodynamics

Not aware of the study group