Ventilating children with congenital heart disease requires meticulous control of pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) to maintain balanced circulation ($Q_p:Q_s$).
Key Physiological Equations & Formulas
- Pulmonary to Systemic Flow Ratio: $$\frac{Q_p}{Q_s} = \frac{SaO_2 - SvO_2}{SpvO_2 - SpaO_2}$$ In single ventricle stage 1 physiology, maintain target $Q_p:Q_s \approx 1.0$ ($SpO_2 75-85\%$).
Practical Clinical Pearls & Bedside Rules
- Manipulating PVR: Hyperoxia ($FiO_2 1.0$), hypocarbia ($PaCO_2 < 35$), alkalosis, and iNO lower PVR (increase $Q_p$). Hypoxia ($FiO_2 0.21$), hypercarbia ($PaCO_2 45-55$), and acidosis raise PVR (decrease $Q_p$).
- Fontan Physiology (Stage 3): Pulmonary blood flow is passive; high intrathoracic pressure or high PEEP will severely depress transpulmonary gradient and cardiac output. Extubate early.
Initial Settings & Clinical Titration Protocol
| Parameter | Recommended Initial Setting | Titration Goal / Safety Threshold |
|---|---|---|
| Stage 1 Norwood Settings | FiO2 0.21, PEEP 4-5 cmH2O, normal PaCO2 40-45 mmHg | Target SpO2 strictly 75-85%. |
| Glenn / Fontan Settings | Low PEEP (3-4 cmH2O), low peak pressures, early extubation | Maintain spontaneous negative intrathoracic breathing. |
Bedside Troubleshooting & Red Flags
Warning
Pulmonary Overcirculation ($SpO_2 > 90\%$ in Shunt): Leads to systemic hypoperfusion, coronary ischemia, and shock. Hypoventilate slightly (PaCO2 45-50) and reduce FiO2.
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.