Ventilator-Induced Lung Injury (VILI) results from mechanical stress and strain exerted on fragile alveolar-capillary membranes by positive pressure ventilation.
Key Physiological Equations & Formulas
Mechanical Power Equation (Gattinoni Simplified):
$$\text{Power} = 0.098 \times V_T \times RR \times \left[ P_{peak} - \frac{\Delta P}{2} \right]$$Expressed in Joules/minute (J/min). Threshold for high VILI risk: >17-20 J/min.
Driving Pressure:
$$\Delta P = \frac{V_T}{C_{stat}} = P_{plat} - PEEP$$Keep driving pressure strictly < 14-15 cmH2O.
Practical Clinical Pearls & Bedside Rules
- The Four VILI Mechanisms: 1. Barotrauma (high pressure), 2. Volutrauma (alveolar overdistension), 3. Atelectrauma (shear stress from cyclic opening/closing), 4. Biotrauma (systemic inflammatory cytokine release).
- Baby Lung Concept: In ARDS, the aerated functional lung tissue is reduced to the size of a healthy 5-6 year old child's lung. Scale tidal volumes strictly to this capacity.
Initial Settings & Clinical Titration Protocol
| Parameter | Recommended Initial Setting | Titration Goal / Safety Threshold |
|---|---|---|
| Tidal Volume Target | 4-6 mL/kg PBW | Safe low-tidal volume ventilation. |
| Plateau Pressure Limit | Pplat <= 30 cmH2O | Absolute upper limit of static alveolar pressure. |
Bedside Troubleshooting & Red Flags
Warning
High Driving Pressure Alert: If driving pressure > 15 cmH2O despite 6 mL/kg PBW, decrease Vt to 5 or 4 mL/kg, verify PEEP, and consider prone positioning.
Key Takeaways & Summary
- Always evaluate patient synchrony and physiological response before changing ventilator parameters.
- Maintain lung-protective strategies to minimize driving pressure ($\Delta P$) and mechanical power.
- Continuously reassess liberation and extubation readiness on daily morning rounds.