Mechanical Ventilation — Setup & Monitoring

Mechanical ventilation provides positive-pressure breaths through an endotracheal or tracheostomy tube when a client cannot maintain adequate gas exchange independently. The three core modes tested on NCLEX are Assist-Control (AC), Synchronized Intermittent Mandatory Ventilation (SIMV), and Pressure Support (PS). In AC, the ventilator delivers a set tidal volume (typically 6–8 mL/kg ideal body weight) for every breath the client triggers or at the set rate — whichever is higher. Risk: hyperventilation and respiratory alkalosis if the client breathes rapidly. SIMV delivers mandatory breaths at a set rate but allows spontaneous breaths in between at whatever volume the client generates, making it useful for weaning. PS augments the client's own spontaneous breaths with a preset pressure boost; the client must initiate every breath (no mandatory rate is set), so PS is used during weaning or with an intact respiratory drive. Key settings the nurse monitors include tidal volume, respiratory rate, FiO2 (started high then titrated down to keep SpO2 ≥ 94%, or ≥ 88–92% for CO2 retainers), and PEEP (positive end-expiratory pressure, typically 5 cmH2O baseline, which prevents alveolar collapse). The nurse verifies ETT placement by confirming bilateral breath sounds, CO2 detection, and chest X-ray. ABGs are drawn 20–30 minutes after any setting change to evaluate effectiveness.