NIRS monitoring during steep trendelenburg in robotic prostatectomy

Robotic-assisted laparoscopic prostatectomy (RALP) requires steep Trendelenburg positioning and CO₂ pneumoperitoneum, which may significantly influence cerebral hemodynamic homeostasis. While postoperative neurological complications are uncommon, there is concern regarding increased intracranial pressure and potential edema during prolonged procedures. Near-infrared spectroscopy (NIRS) allows continuous monitoring of cerebral oxygenation, rSO2 reflects the balance between oxygen delivery and consumption, integrating changes of oxygenated hemoglobin (ΔHbO2) and deoxygenated hemoglobin (ΔHHb). This study aimed to evaluate phase-dependent changes in cerebral oxygenation (rSO₂, ΔO₂Hb, ΔHHb) and optic nerve sheath diameter (ONSD) during RALP, and to assess their temporal correlation. This prospective observational study enrolled forty adult patients (ASA I-III) undergoing RALP in steep Trendelenburg position (30 degrees) at Nuovo Ospedale di Prato, Italy, between November 2024 and May 2025. Cerebral oxygenation was continuously monitored using near-infrared spectroscopy (NIRS). ONSD was measured bilaterally using ultrasound at predefined time points: baseline (T0), 45 min after Trendelenburg positioning (T1), 120 min after Trendelenburg (T2), during vesicourethral anastomosis (T3), and before extubation in neutral position (T4). Pearson correlation coefficients were calculated to assess the association between NIRS-derived parameters and ONSD changes. Compared with baseline, Trendelenburg positioning was associated with significant phase-dependent changes in cerebral oxygenation and hemoglobin-derived parameters. rSO₂ and ΔO₂Hb increased during early and prolonged Trendelenburg phases, peaking during vesicourethral anastomosis (T3), and partially decreased after return to supine position (T4). ΔHHb demonstrated a progressive increase during later intraoperative phases, reaching highest values at T3 and T4. ONSD increased progressively across phases on both sides (right: 3.79 ± 0.36 mm at T0 to 4.59 ± 0.47 mm at T3; left: 3.80 ± 0.42 mm to 4.73 ± 0.47 mm). Correlation analysis demonstrated a moderate-to-strong association between ΔHHb and ONSD (right: r = 0.63, p < 10⁻¹⁶; left: r = 0.63, p < 10⁻¹⁶), supporting temporal coupling between cerebral deoxygenated hemoglobin accumulation and optic nerve sheath expansion. This study demonstrates distinct phase-dependent cerebral oxygenation patterns during RALP. The late-phase increase in ΔHHb occurring alongside ONSD enlargement may reflect cerebral venous congestion, a mechanism potentially involved in cerebral edema development during prolonged steep Trendelenburg positioning.