Severe pediatric asthma causes intense bronchospasm, mucosal edema, and mucus plugging, creating severe expiratory flow limitation and dynamic hyperinflation.
Key Physiological Equations & Formulas
- Intrinsic PEEP Measurement: $$PEEP_i = P_{exp,hold} - PEEP_{set}$$ Direct measurement of trapped gas pressure causing alveolar hyperinflation and venous compression.
Practical Clinical Pearls & Bedside Rules
- Expiratory Time Rules: Set low respiratory rates (10-18 bpm in school-age, 15-22 in toddlers) with long expiratory times (I:E ratio 1:4 to 1:5) to allow complete exhalation.
- Permissive Hypercapnia: Do NOT attempt to normalize PaCO2; accept PaCO2 60-90 mmHg with pH >= 7.15-7.20 to avoid catastrophic barotrauma.
Initial Settings & Clinical Titration Protocol
| Parameter | Recommended Initial Setting | Titration Goal / Safety Threshold |
|---|---|---|
| Mode | Volume Control (constant square flow) or Pressure Control with long Te | Monitor Pplat closely (keep Pplat < 30 cmH2O). |
| Inspiratory Flow | High peak flows (40-60 L/min) | Shortens Ti, maximizing time available for expiration. |
Bedside Troubleshooting & Red Flags
Warning
Sudden Hemodynamic Collapse after Intubation: Disconnect patient from ventilator circuit immediately and manually compress chest to relieve dynamic air-trapping tension.
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.