Ventilator Waveform Analysis: Auto-PEEP

Ventilator waveform analysis is the systematic interpretation of pressure-time, flow-time, and volume-time scalar graphics displayed on the mechanical ventilator to assess respiratory mechanics and optimize ventilation. The pressure-time waveform shows peak inspiratory pressure (PIP) reflecting total airway resistance plus lung/chest wall compliance, and plateau pressure (Pplat) reflecting alveolar distending pressure (static compliance). The difference between PIP and Pplat represents resistive pressure from airway resistance. The flow-time waveform displays inspiratory and expiratory flow patterns; in normal conditions, expiratory flow returns to zero baseline before the next breath. Auto-PEEP (intrinsic PEEP) is detected when expiratory flow does NOT return to zero before the next inspiration, indicating air trapping -- confirmed by performing an end-expiratory hold maneuver. The volume-time waveform shows tidal volume delivery and return; incomplete return to baseline indicates air leak or air trapping. Static compliance (Cst) = tidal volume / (Pplat - total PEEP), with normal being 60-100 mL/cmH2O; decreased compliance indicates stiff lungs (ARDS, pulmonary fibrosis, atelectasis, pneumothorax). Airway resistance (Raw) = (PIP - Pplat) / flow, with normal being 5-10 cmH2O/L/s; increased resistance indicates bronchospasm, mucus plugging, or...