Mechanical ventilation settings

At the time of renal blood flow assessment, all patients were deeply sedated and paralyzed with continuous infusion of cis-atracurium 1–3 mcg/kg/min for clinical reasons. Mechanical ventilation settings included constant-flow controlled ventilation, a tidal volume of 6 ml/kg of ideal body weight and the PEEP level titrated to the lowest driving pressure. [14, 15] Briefly, PEEP was increased by 2 cm H₂O step starting from 6 cm H₂O, up to the PEEP level leading to a static end-inspiratory plateau pressure (P_PLAT) of 28–30 cm H₂O; then, the PEEP level corresponding to the lowest driving pressure was chosen.

The driving pressure was measured as:

where PEEP_TOT is the total static positive end-expiratory pressure. P_{PLAT and} PEEP_TOT were measured through the occlusion technique (i.e. a 4 s airway opening occlusion maneuver at end-inspiration and end-expiration, respectively) [16].