Laparoscopic gastric sleeve gastrectomy is becoming an increasingly frequent procedure for patients with severe obesity and its related diseases, such as type 2 diabetes, hypertension, dyslipidemia, and sleep apnea.

Assessing the optic nerve sheath diameter (ONSD) with noninvasive ultrasonography has shown to be accurate in determining increased ICP as pressure changes in the subarachnoid space and the cerebrospinal fluid reflect variations in the optic nerve sheath (ONS).

The investigators hypothesized that if ICP during laparoscopy is different according to the position, ONSD would likewise be different. Thus, investigators will investigate the change of ONSD according to the positional change in laparoscopic sleeve gastrectomy surgery.

Laparoscopic gastric sleeve gastrectomy is becoming an increasingly frequent procedure for patients with severe obesity and its related diseases, such as type 2 diabetes, hypertension, dyslipidemia, and sleep apnea.

The impacts of laparoscopy on the intracranial pressure (ICP) are well-documented and several studies have demonstrated that the induction of artificial pneumoperitoneum provokes a measurable increase in ICP. The mechanisms of increase of ICP during laparoscopy are suggested as follows: increase of intra-abdominal pressure, impairment of cerebrospinal fluid (CSF) absorption and impeded drainage of the lumbar venous plexus, increased pressure in the vascular compartment of sacral spaces, Trendelenburg position, and cerebral vasodilation due to hypercarbia.

Neurological comorbidities resulting in chronically elevated ICP-pseudotumor cerebri and idiopathic intracranial hypertension-may develop in morbidly obese individuals without discernable clinical manifestations.

Assessing the optic nerve sheath diameter (ONSD) with noninvasive ultrasonography has shown to be accurate in determining increased ICP as pressure changes in the subarachnoid space and the cerebrospinal fluid reflect variations in the optic nerve sheath (ONS) .

A study on ultrasonographic measurement of ONSD laparoscopic radical prostatectomy with steep Trendelenburg positioning revealed that ONSD increased approximately 12.5% and the increase of ICP corresponding to change of ONSD could be predicted. However, no study measured the changes of ONSD according to the positional change with reversed Trendelenburg position during laparoscopic sleeve gastrectomy. The investigators hypothesized that if ICP during laparoscopy is different according to the position, ONSD would likewise be different. Thus, investigators will investigate the change of ONSD according to the positional change in laparoscopic sleeve gastrectomy surgery.

Inclusion Criteria:

• patients older than 18 years old undergoing laparoscopic sleeve gastrectomy under general anesthesia.

Exclusion Criteria:

• pre-existing neurological (e.g. hydrocephalus, intracranial hemorrhage, Etc.) Or cerebrovascular disease, past medical history of ocular pathology or surgery and the use of ketamine and/or succinylcholine during anesthesia.