Inhaled nitric oxide (iNO) and nebulized epoprostenol selectively vasodilate ventilated pulmonary capillary beds, improving V/Q matching and lowering pulmonary arterial pressure without systemic hypotension.
Key Physiological Equations & Formulas
- Nitric Oxide Mechanism: $$\text{L-Arginine} \rightarrow \text{NO} \rightarrow \text{sGC} \rightarrow \text{cGMP} \rightarrow \text{Vasodilation}$$ Inactivated immediately upon contact with hemoglobin to form methemoglobin.
Practical Clinical Pearls & Bedside Rules
- Standard Starting Dose: Start iNO at 20 ppm. Higher doses (>20 ppm) rarely improve oxygenation but significantly increase methemoglobin and nitrogen dioxide ($NO_2$) toxicity.
- Weaning Protocol: Wean gradually: 20 -> 10 -> 5 -> 2 -> 1 ppm before discontinuation to prevent life-threatening rebound pulmonary hypertension.
Initial Settings & Clinical Titration Protocol
| Parameter | Recommended Initial Setting | Titration Goal / Safety Threshold |
|---|---|---|
| Initial Dose | 20 ppm | Assess response within 30-60 minutes (rise in PaO2 > 20 mmHg or OI drop > 20%). |
| Methemoglobin Surveillance | Monitor co-oximetry daily (keep MetHb < 2.5-3.0%) | If MetHb > 5%, reduce iNO dose. |
Bedside Troubleshooting & Red Flags
Warning
Rebound Pulmonary Hypertension: Abrupt discontinuation of iNO can cause fatal acute right ventricular failure. Never stop iNO abruptly.
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.