A Comparative Study of Ventilation Strategies in Different Surgical Positions on Intracranial Pressure and Cerebral Blood Flow During Laparoscopic Surgery

Variable tidal volume ventilation (V-VCV) ：The initial tidal volume is set at 6-8 ml/kg IBW according to the Ideal Body Weight (IBW), and the maximum tidal volume (Vt\_max) and minimum tidal volume (Vt\_min) are set at 10-20% of the base tidal volume (Vt\_base). Respiratory Rate 12. Inspiratory Flow Rate (IFR) 60L/min, Inspiration to Expiration Ratio (IER) 1:2, Positive End-Expiratory Pressure (PEEP) 5 cm water column, and Inhaled Oxygen Concentration (FiO2) 41%.

Pressure-regulated volume-controlled ventilation (PRVC) ：Initial tidal volume is set at 6-8 ml/kg IBW based on Ideal Body Weight (IBW), peak inspiratory pressure is capped at 30 cmH2O, maximum tidal volume (Vt\_max), and minimum tidal volume (Vt\_min) is set at 10-20% of basal tidal volume (Vt\_base). Respiratory Rate (RR) 12, Inspiratory Breathing Ratio (IBR) 1:2, Positive End-Expiratory Pressure (PEEP) 5 cm water column, and Inhaled Oxygen Concentration (FiO2) 98%.

Conventional volume-controlled ventilation (C-VCV) ：The initial tidal volume is set at 6-8 ml/kg IBW based on Ideal Body Weight (IBW), and the maximum tidal volume (Vt\_max) and minimum tidal volume (Vt\_min) are set at 10-20% of the basal tidal volume (Vt\_base). Respiratory Rate 12. Inspiratory Flow Rate (IFR) 60L/min, Inspiration to Expiration Ratio (IER) 1:2, Positive End-Expiratory Pressure (PEEP) 5cm water column, FiO2 98%.

Pressure-controlled ventilation (PCV)：Set inspiratory pressure level, usually 20 cmH2O initial value, Respiratory Rate 12, Inspiratory to Expiratory Ratio 1:2, Positive End-Expiratory Pressure (PEEP) 5 cm water column, Inhaled Oxygen Concentration (FiO2) 98%.

Trendelenburg position：Lower the head of the bed by 30 degrees with no more than 15 degrees of lateral tilt.

Reverse Trendelenburg position：Elevate the head of the bed by 30 degrees with no more than 15 degrees of lateral tilt.