Assessment of Optic Sheat Diameter (ONSD) and Eyeball Transverse Diameter (ETD) Ratio Measurement From Ocular Ultrasound

Assessment of Increased Intracranial Pressure by Optic Nerve Sheath Diameter (ONSD), Eyeball Transverse Diameter (ETD) and ONSD/ETD Ratio Measurement From Ocular Ultrasound

The aim of this study is to evaluate the effects of different carbon dioxide gas insufflation pressures on the ultrasound-guided optic nerve sheath diameter in patients undergoing laparoscopic cholecystectomy and to determine the possible relationship between these changes and intracranial pressure. The study aims to gain a better understanding of the neurophysiological effects of gas pressures used during laparoscopic surgery and to obtain scientific data aimed at improving patient safety.

Laparoscopic surgeries are now widely preferred in the treatment of gallbladder diseases. Carbon dioxide (CO₂) pneumoperitoneum created during laparoscopic surgery and the surgical positions applied can lead to temporary physiological changes in intracranial pressure (ICP). Increased intra-abdominal pressure can trigger an increase in ICP by reducing venous return, increasing intrathoracic pressure, and causing hypercapnia. Since direct measurement of increased intracranial pressure requires invasive methods, it is not applicable to every patient in clinical practice. Optic nerve sheath diameter (ONSD) measurement, performed with transorbital ultrasonography, is a non-invasive, bedside method that can indirectly reflect changes in ICP. Literature shows that an increase in ONSD correlates with increased ICP and can be a reliable monitoring method during laparoscopic surgeries. Furthermore, to reduce the impact of inter-individual ocular anatomical differences on measurement results, the ratio of optic nerve sheath diameter to eyeball transverse diameter (ONSD/ETD) will be calculated. The literature reports that the ONSD/ETD ratio exhibits lower variability compared to ONSD measurement alone and may be a more reliable parameter for reflecting intracranial pressure changes. However, studies comparing the effects of different gas insufflation pressures on ONSD/ETD in laparoscopic cholecystectomy surgeries are limited.

Measurements of ONSD (On-Surgery Pressure) have shown that pneumoperitoneum created during these surgeries can increase intracranial pressure in both the early and late stages. Literature reports that ONSD values in the range of 5.0-5.9 mm may be associated with increased ICP. While current studies reveal the effects of pneumoperitoneum duration, surgical position, and hypercapnia on ICP, data on the comparative effects of different gas insufflation pressures are limited. Therefore, evaluating the effects of low and standard insufflation pressures on ONSD during laparoscopic cholecystectomy aims to fill this gap in the current literature. This study has the potential to contribute to determining safer pressure ranges in laparoscopic surgical procedures.

Inclusion Criteria:

• Patients aged between 18 and 80 years.
• Patients scheduled for laparoscopic cholecystectomy.
• ASA (American Society of Anesthesiologists) physical status I or II.

Exclusion Criteria:

• History of intracranial space-occupying lesion or high intracranial pressure (ICP).
• History of abdominal trauma.
• History of orbital/ocular trauma.