Increase of intracerebral pressure (ICP) during laparoscopic surgery has known to be associated with positional changes. Optic nerve sheath diameter (ONSD) has correlation with ICP and ultrasonographic measurement of optic nerve sheath diameter (ONSD) is known to be a noninvasive and rapidly applicable technique for evaluating ICP. The aim of this study is to investigate the change of ONSD according to the positional change during laparoscopic surgery.

1. Purpose There can be many physiologic changes during laparoscopic surgery. Increase of intracerebral pressure (ICP) is one of them, which has known to be associated with arterial concentration of carbon dioxide or positional changes. Changes of ICP can be measured directly by invasive method. However, optic nerve sheath diameter (ONSD) has correlation with ICP and ultrasonographic measurement of optic nerve sheath diameter (ONSD) is known to be a noninvasive and rapidly applicable technique for evaluating ICP. The aim of this study is to investigate the change of ONSD according to the positional change during laparoscopic surgery.

2. Hypothesis Changes of ONSD will be shown according to the positional change during laparoscopic surgery, and these can reflect the changes of ICP.

3. Objectives Female patients who are scheduled to undergo laparoscopic surgery, American society of anesthesiologist class (ASA) I-II, aged between 19 to 65 years, are allocated into 2 groups.

   • Group 1: Laparoscopic gynecological surgery, (Trendelenburg position)
   • Group 2: Laparoscopic cholecystectomy, (Reverse trendelenburg position)

4. Methods Patients are premedicated with midazolam 0.5 mg/kg before transported to the operating room. Once in the operating room, patients were monitored with electrocardiography, non invasive blood pressure, pulse oximetry (Datex-Ohmeda S/5, Planar Systems, Inc., Beaverton, OR, USA) and BIS (Aspect 2000, Aspect Medical Systems, Inc., Newton, MA, USA).

   Anesthesia are induced with propofol (2mg/kg) and followed by administering rocuronium 0.6 mg/kg. After tracheal intubation, the lungs of the patients were then ventilated with oxygen in air (1:2) using a tidal volume of 8-10 mL/kg and a respiratory rate of 10-12/min, and the ventilation rate was adjusted to maintain the end-tidal carbon dioxide partial pressure between 35 and 40 mmHg and peak inspiratory pressure below 30 cmH2O. Anesthesia is maintained with desflurane in addition to the continuous infusion of remifentanil. Radial arterial cannulation is done for invasive arterial blood pressure monitoring.

   After induction of anesthesia, when stabilization of cardiovascular status is achieved, optic nerve sheath diameter (ONSD) is measured by ultrasonographic measurement. Patients were placed in the supine position with their eyes closed, and a thick gel layer was applied to the closed upper eyelid. The 7.5-MHz linear probe was placed on the gel without excessive pressure and adjusted to the proper angle for displaying the entry of the optic nerve into the globe. The intensity of the ultrasound was adjusted to display optimal contrast between the retrobulbar echogenic fat tissue and the vertical hypoechoic band. An ultrasound beam was focused on the retrobulbar area (4 cm deep) using the lowest possible acoustic power that could measure ONSD. The ONSD was measured 3 mm behind the optic disc. Measurements were performed in the transverse and sagittal planes of both eyes, and the final ONSD value was calculated by averaging 4 measured values.

   ONSD was measured at 7 serial time points during surgery:

   1. Preinduction (prior to the induction of anesthesia in the operating room)
   2. 5 minutes after induction of anesthesia
   3. 5 minutes after introducing pneumoperitoneum
   4. 5 minutes after positional change
   5. 15 minutes after positional change
   6. 30 minutes after positional change
   7. 5 minutes after discontinuing pneumoperitoneum Arterial blood gas analysis is performed to evaluate the arterial carbon dioxide concentration (PaCO2) level at each time point.

5. Statistical Analysis All data are expressed as numbers (%) or mean ± standard deviation. Repeated measures ANOVA will be performed to compare the parameters at specific time points during surgery.

Inclusion Criteria:

• Female patients who are scheduled to undergo laparoscopic surgery, American society of anesthesiologist class (ASA) I-II, aged between 19 to 65 years

Exclusion Criteria:

• Aged unger 18 years or over 65 years
• American society of anesthesiologist class (ASA) III-IV
• Patients with increased intracranial pressure (e.g. hydrocephalus, intracranial hemorrhage, etc.)
• Patients with opthalmologic disease