Purpose: The purpose of this study was to assess the extent of the increased intracranial pressure (ICP) resulting from CO2 pneumoperitoneum and steep Trendelenburg positioning using ultrasonographic measurement of optic nerve sheath diameter (ONSD) in patients undergoing robot-assisted laparoscopic radical prostatectomy (RALRP). Patients and Methods: Twenty patients who underwent elective RALRP were enrolled in this study. ONSD and regional cerebral oxygen saturation (rSO2) were investigated noninvasively using ocular ultrasonography and near-infrared spectroscopy before anesthesia (T0), 10 minutes after anesthesia induction in the supine position (T1), 10 and 30 minutes after CO2 pneumoperitoneum with 30-degree Trendelenburg positioning (T2 and T3), and after returning to supine position without CO2 pneumoperitoneum at the conclusion of the RALRP (T4). Results: The mean values of ONSD at all time points (T1, T2, T3, and T4) after general anesthesia significantly increased compared with that before general anesthesia (T0). During CO2 pneumoperitoneum with 30-degree Trendelenburg positioning (T2, T3), a significant increase of 12.5% in ONSD was observed in comparison with ONSD after anesthesia induction in the supine position without CO2 pneumoperitoneum (T1). Three patients had an ONSD value equivalent to an ICP above 20 mm Hg, and these patients did not experience a decrease of rSO2 or any neurologic complications. Conclusions: In patients undergoing RALRP, the increase of 12.5% in ONSD during CO2 pneumoperitoneum with steep Trendelenburg positioning was observed and thus the increase of ICP corresponding to this change of ONSD could be predicted. In 15% of the enrolled patients, ONSD increased by values equivalent to an ICP above 20 mm Hg without a deterioration of rSO2 or any neurologic complications.
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