Pneumoperitoneum at 8 versus 12 mmHg and cerebral haemoglobin dynamics during robot-assisted radical prostatectomy: a sequential observational cohort study

Background Pneumoperitoneum pressure is a modifiable component of robot-assisted radical prostatectomy (RALP), but its association with cerebral haemodynamics during prolonged steep Trendelenburg positioning remains incompletely defined. We examined whether pneumoperitoneum at 8 versus 12 mmHg was associated with differences in NIRS-derived cerebral haemoglobin dynamics, optic nerve sheath diameter (ONSD), and postoperative patient-reported visual function. Methods This sequential observational cohort study included 72 patients undergoing RALP. The low-pressure group (8 mmHg; n = 36) was derived from a previously published prospective cohort that had addressed a different physiological research question, whereas a subsequent standard-pressure cohort (12 mmHg; n = 36) was prospectively recruited using the same eligibility criteria, perioperative management, monitoring protocol, and outcome assessment. Cerebral haemodynamics were assessed using bilateral NIRS-derived haemoglobin indices and ONSD ultrasonography. Postoperative visual function was assessed using Catquest-9SF Rasch analysis. Inverse probability of treatment weighting (IPTW) was used as a sensitivity analysis for measured differences in surgical complexity. Results Standard-pressure pneumoperitoneum was associated with greater ONSD enlargement and greater changes in deoxygenated haemoglobin (ΔHHbi) and regional cerebral oxygen saturation (ΔrSO₂) than low-pressure pneumoperitoneum. These differences remained directionally consistent after IPTW adjustment for measured surgical-complexity variables. The postoperative change in Catquest-9SF Rasch score was greater in the 12-mmHg cohort, whereas the incidence of self-reported visual disturbances did not differ significantly between groups. Conclusions Compared with 8 mmHg, pneumoperitoneum at 12 mmHg was associated with a greater increase in cerebral deoxygenated haemoglobin and ONSD during RALP, a physiological pattern compatible with greater impairment of cerebral venous drainage. Because the cohorts were sequential and non-randomised, these findings require confirmation in randomised studies.