Group I patients received mechanical ventilation using the PC mode. The anesthetic machine (MAQUET Flow-I, Italy) parameters were set as follows: The inspiratory pressure (Pins) was adjusted to maintain an end-tidal carbon dioxide concentration (ETCO2) of 4.0-5.0 kPa. Pure oxygen and air were utilized at 0.3 L/min each, with an oxygen content of 41%.

Group II patients received mechanical ventilation in VC mode. The tidal volume during regulated breathing was determined based on the ideal body weight (IBW): 6-8 ml/kg (IBW for males: 50 + 0.91 × (height [cm] - 152.4); IBW for females: 45.5 + 0.91 × (height [cm] - 152.4). The positive end-expiratory pressure (PEEP) was set at 10 cmH2O, with an inspiration-to-expiration ratio of 1:2, a respiratory rate of 16 breaths per minute, and an oxygen content of 41%

Group III patients received mechanical ventilation using the PRVC mode.The tidal volume during regulated breathing was determined based on the ideal body weight (IBW): 6-8 ml/kg (IBW for males: 50 + 0.91 × (height [cm] - 152.4); IBW for females: 45.5 + 0.91 × (height [cm] - 152.4). The positive end-expiratory pressure (PEEP) was set at 10 cmH2O, with an inspiration-to-expiration ratio of 1:2, a respiratory rate of 16 breaths per minute, and an oxygen content of 41%

Patients were randomly assigned to three groups using a random number table and the random remainder grouping method at a ratio of 1:1:1. Group I received pressure control ventilation (PC).

Patients were positioned supine with their eyes softly closed, and their eyes were protected with disposable transparent patches. A 7.5 MHz linear probe (Micromaxx Ultrasound System; SonoSite Inc., Bothell, WA, USA) was gently placed on the closed upper eyelid without applying pressure to the eyeball, and sufficient ultrasound gel was applied to ensure clear imaging. The optic nerve sheath was checked and measured 3 mm beyond the globe, and three ONSD measures were performed, with the average value utilized as the final ONSD measurement, which was accurate to 0.01 mm.

Arterial blood carbon dioxide partial pressure, is an important indicator of alveolar ventilation, reflecting the respiratory factors in acid-base balance. Its reference value is usually 35-45 mmHg.

Mean airway pressure throughout the ventilation cycle

Maximum pressure in the airway throughout inspiration

Esophageal manometry is the recording of pressure changes in various parts of the esophagus at rest and after swallowing, and is used to indicate the motor function of the upper and lower esophageal sphincters and the body of the esophagus, and to understand esophageal motility

Tidal volume is the volume of gas inhaled or exhaled each time when breathing calmly, it is an indicator to show lung volume, mainly used for ventilation function test in pulmonary function test. Tidal volume is the basis for assessing lung function and ventilation efficiency, and is an important indicator of lung volume