Clinical meaning
Non-invasive ventilation (NIV) delivers positive pressure ventilation through a face mask, nasal mask, or helmet interface without endotracheal intubation. Two primary modes: CPAP (continuous positive airway pressure) applies a single constant pressure throughout the respiratory cycle, acting as a pneumatic splint to prevent alveolar collapse, reduce preload (beneficial in cardiogenic pulmonary edema), and improve FRC. BiPAP (bilevel positive airway pressure) provides two pressure levels: IPAP (inspiratory positive airway pressure) augments tidal volume and reduces work of breathing, while EPAP (expiratory positive airway pressure) functions like PEEP to prevent alveolar collapse. The difference between IPAP and EPAP determines the pressure support level (driving pressure). NIV has strongest evidence in COPD exacerbation (reduces intubation by 65%, mortality by 46%) and acute cardiogenic pulmonary edema (rapidly improves oxygenation and reduces preload).
Diagnosis & workup
Diagnostics & workup: - ABG before initiating NIV: baseline pH, PaCO2, PaO2 (target pH improvement >0.03 within 1-2 hours) - Continuous SpO2 monitoring - ABG repeat at 1-2 hours: if pH not improving, NIV is failing — consider intubation - Respiratory rate monitoring: should decrease with effective NIV - Tidal volume monitoring on ventilator display: target 6-8 mL/kg - Mask leak assessment: >25% leak impairs effectiveness - GCS monitoring: worsening mental status on NIV = failure