Flow- Versus Volume-controlled Ventilation During Robot-assisted Laparoscopic Radical Prostatectomy

The primary outcome is the PaO2/FiO2 before extubation (T4).

Driving pressure is measured as the difference between plateau pressure and positive end-expiratory pressure (PEEP), with values obtained directly from the ventilator display in the VCV group. In the FCV group, tracheal driving pressure is recorded from the ventilator and corrected for endotracheal tube resistance to calculate alveolar driving pressure, allowing physiologically comparable measurements between groups.

Mechanical power (MP) is calculated from recorded ventilatory parameters. In the volume-controlled ventilation (VCV) group, MP is calculated using respiratory rate, tidal volume, peak airway pressure, and driving pressure. In the flow-controlled ventilation (FCV) group, MP is calculated using minute ventilation, peak pressure, PEEP, and inspiratory flow.

Lung ultrasound (LUS) examination is performed with the patient in the supine position using an ultrasound device equipped with a low-frequency (2.5-5 MHz) convex probe suitable for intercostal imaging. The thoracic surface is systematically evaluated in both longitudinal and transverse planes. For standardized assessment, each hemithorax is divided into anterior, lateral, and posterior regions, and each region is further subdivided into upper and lower areas, resulting in a total of 12 scanning zones. Normal aeration, defined as the presence of A-lines or fewer than two isolated B-lines with preserved lung sliding, is scored as 0. The presence of three or more well-spaced B-lines with preserved sliding is scored as 1. Coalescent B-lines indicating moderate loss of aeration are scored as 2. Pulmonary consolidation is scored as 3. The total LUS score ranges from 0 to 36, with higher scores indicating greater loss of lung aeration.