Neurally Adjusted Ventilatory Assist (NAVA) and Proportional Assist Ventilation (PAV+) deliver pressure support in exact proportion to patient effort, maximizing synchrony and minimizing sedation needs.
Key Physiological Equations & Formulas
NAVA Pressure Delivery:
$$P_{aw} = \text{NAVA level} \times Edi + PEEP$$Delivered pressure is directly proportional to diaphragmatic electrical activity ($Edi$ in $\mu V$).
PAV+ Equation:
$$P_{aw} = (\% \text{assist}) \times [(\text{Flow} \times R_{aw}) + (\text{Volume} \times E_{rs})]$$Ventilator calculates real-time elastance and resistance to unload a fixed percentage of total work.
Practical Clinical Pearls & Bedside Rules
- Neural Triggering: NAVA triggers and cycles off based on diaphragmatic electrical activity, completely bypassing pneumatic delay and pneumatic leaks.
- Diaphragm Protection: Prevents both diaphragm disuse atrophy (over-assistance) and eccentric load injury (under-assistance).
Initial Settings & Clinical Titration Protocol
| Parameter | Recommended Initial Setting | Titration Goal / Safety Threshold |
|---|---|---|
| NAVA Level Setting | 0.5 - 2.0 cmH2O/microvolt | Titrate to achieve normal Edi peak (5-15 microvolts) and comfortable breathing pattern. |
| Backup Ventilation | Always configure PC/VC backup | Ensures safety if Edi signal is lost or central apnea occurs. |
Bedside Troubleshooting & Red Flags
Warning
Loss of Edi Signal: Check Edi catheter position using the ventilator positioning tool (retrocardiac P-waves and QRS complexes).
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.