Evaluation of optic nerve sheath diameter in patients undergoing robotic assisted laparoscopic prostatectomy

Background: Nowadays, technological advancements enable many surgical procedures to be performed laparoscopically. Robot-assisted laparoscopic prostatectomy (RALP) has been increasingly utilized due to its many advantages over open prostatectomy, such as reduced complications, minimal blood loss, lower complication rates, and consequently, shorter hospital stays. Robot-Assisted Radical Prostatectomy (RARP) is the most common procedure among robotic-assisted urologic surgeries (1). Laparoscopy requires the operator to use deep Trendelenburg positioning and CO2 pneumoperitoneum to improve visual fields. The use of this technique can lead to adverse hysiological effects involving multiple organs and systems, including the central nervous system. Elevated intraabdominal pressure (IAB), reduced venous return, and increased intracranial pressure (ICP) are some of the systemic physiological consequences that can develop as a result of pneumoperitoneum and deep Trendelenburg positioning (2,3,4). Several attempts have been made to assess the optic nerve sheath diameter (ONSD) using ocular ultrasound to determine the presence or severity of elevated ICP during laparoscopic surgery in various positions. Previous studies have shown that the transorbital ultrasonographic measurement of ONSD correlates with the degree of ICP and can detect intracranial hypertension in various clinical settings(2,6,12,20). Ultrasonographic measurement of ONSD is a simple, non-invasive, yet reliable technique for ICP assessment and can detect intracranial hypertension (11,19,24). The aim of this study was to investigate changes in ONSD at different times during surgery in patients undergoing RALP. We also analyzed the influence of age, body mass index (BMI), end-tidal carbon dioxide (ETCO2), PİP inspiratory pressure (PIP), mean arterial blood pressure (MAP), duration of surgery, and STP on ONSD during RARP. Materials and Methods: This prospective observational study included 75 patients who underwent Robot-Assisted Laparoscopic Prostatectomy (RALP) at the Urology Department of Akdeniz University Hospital. Patients were excluded if they had a history of cerebrovascular accidents (such as brain injury, cerebral aneurysm, or brain tumor), cognitive diseases, a Glasgow Coma Scale (GCS) score less than 15, a diagnosis of glaucoma, high intraocular pressure, or if they refused to participate. The study protocol was approved by the hospital's ethics board, and all participants provided written informed consent. Examinations were performed using a high-frequency 7.5-12 Hz linear transducer. Measurement Time Points: • P1: 20 minutes after the induction of general anesthesia in a supine position • P2: 10 minutes after insufflation of the abdomen with CO2 in a supine position • P3: 30 minutes into a 45° Trendelenburg position with the abdomen still insufflated with CO2 • P4: During the control of Santorini's plexus in a 45° Trendelenburg position with CO2 still insufflated • P5: 10 minutes after administering Mannitol in a supine position We investigated the influence of circulatory parameters (SBP, DBP,MAP ) and respiratory parameters (PIP, SPO2, ETCO2, PEEP), as well as patient-specific factors (age, BMI, comorbidities) and time-dependent factors on the Optic Nerve Sheath Diameter (ONSD). Results: The study included 75 patients with a mean age of 65.79 ± 6.92 years and a mean BMI of 29.08 ± 4.01 kg/m². We found that 6.7% of patients were ASA-I, 66.7% were ASA-II, and 26.7% were ASA-III. A positive correlation was observed between the measured ONSD and patients with hypertension (HT) (p=0.021). Significant correlations were also found between ONSD and BMI (r=0.282; p=0.014). The ONSD measurements were: P1 at 3.9 mm (±0.49 mm), P2 at 4.6 mm (±0.61 mm), P3 at 4.96 mm (±0.53 mm), P4 at 5.0 mm (±0.44 mm), and P5 at 4.2 mm (±0.56 mm), with these differences being statistically significant (p<0.001). In post-hoc analyses, ONSD measurements were significantly different at all times, except between P3 and P4 (p=0.175) (p<0.05). Furthermore, the measurements at P1 and P5 were significantly lower than at P2, P3, and P4 (p<0.001). Correlations between insufflation gas pressure during pneumoperitoneum (P2) and ONSD at P2 and P4 were statistically significant (p<0.04). Moderate and significant relationships were observed between SAD, DAP, MAP values, and ONSD, although the correlations between measured blood pressure values and ONSD were not statistically significant. Conclusions: We concluded that understanding the physiological effects of both the Trendelenburg position and pneumoperitoneum on various systems, and measuring the optic nerve sheath diameter, can complement perioperative monitoring methods for anesthesia management in robot-assisted laparoscopic prostatectomy. Keywords: Optic nerve sheath diameter, Robotic-assisted laparoscopic prostatectomy, Steep Trendelenburg position.