Volume-Controlled and Pressure-Controlled Continuous Mandatory Ventilation are the cornerstones of invasive respiratory support, each having distinct mechanical guarantees and safety profiles.
Key Physiological Equations & Formulas
- Minute Ventilation: $$\dot{V}_E = V_T \times RR$$ Primary determinant of alveolar ventilation and arterial carbon dioxide elimination ($PaCO_2$).
Practical Clinical Pearls & Bedside Rules
- VC-CMV Guarantees Volume: Volume is constant, but airway pressures vary with patient compliance and resistance. Essential to set strict high-pressure alarms.
- PC-CMV Guarantees Pressure: Peak pressure is constant, but tidal volume varies with compliance and resistance. Essential to set strict low/high minute ventilation alarms.
Initial Settings & Clinical Titration Protocol
| Parameter | Recommended Initial Setting | Titration Goal / Safety Threshold |
|---|---|---|
| Mode Selection | VC-CMV or PC-CMV | Choose VC for strict volume/PaCO2 control (TBI), PC for lung protection and severe ARDS. |
| Respiratory Rate | 12-20 bpm (Adult) / 20-30 bpm (Peds) | Titrate to target arterial pH 7.35-7.45 (or permissive hypercapnia in ARDS/Asthma). |
Bedside Troubleshooting & Red Flags
Warning
Sudden Hypoventilation in PC-CMV: A drop in compliance (e.g., mucous plug, atelectasis) will drastically reduce delivered tidal volume. Monitor delivered Vt continuously.
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.