Clinical meaning
Mechanical ventilation provides respiratory support by generating positive pressure to inflate the lungs (opposite of physiologic negative-pressure breathing). Key modes: Assist-Control (AC) - delivers a set tidal volume (volume-targeted) or pressure (pressure-targeted) for every breath, whether triggered by the patient or timed by the ventilator. SIMV - delivers set breaths synchronized with patient effort, with spontaneous breaths between mandatory breaths (no longer preferred due to increased work of breathing during unsupported breaths). Pressure Support (PS) - augments each patient-initiated breath with a set pressure level; used for weaning and spontaneous breathing trials. Initial settings for most patients: AC mode, Vt 6-8 mL/kg ideal body weight (lung-protective), RR 14-16, FiO2 titrated to SpO2 92-96%, PEEP 5-8 cmH2O. Lung-protective ventilation (ARDSNet protocol) limits tidal volume to 6 mL/kg IBW and plateau pressure to <=30 cmH2O to prevent ventilator-induced lung injury (VILI): volutrauma (overdistension), barotrauma (high pressures), atelectrauma (repeated opening/closing of atelectatic alveoli), and biotrauma (inflammatory mediator release from injured alveoli). The ARDSNet trial demonstrated 22% mortality reduction with low tidal volume ventilation in ARDS.