The Neonate with Congenital Diaphragmatic Hernia

This neonate shows signs of persistent pulmonary hypertension of the newborn (PPHN) with pre/postductal saturation difference (92% vs 88%) and a flattened septum on echo, indicating suprasystemic or systemic RV pressure. He is not optimized.

Targets before surgery:

• Preductal SpO2 ≥ 90–95% with minimal FiO2 (avoid hyperoxia - it worsens reperfusion injury and does not improve PPHN)
• PaCO2 45–60 mmHg (permissive hypercapnia) - avoid hyperventilation, which is harmful
• pH ≥ 7.25
• Echocardiographic improvement: septal flattening should resolve or improve; RV pressure < systemic
• Lactate < 3 mmol/L and normal end-organ perfusion

Management:

• Optimize ventilation: avoid high PIP (barotrauma to the hypoplastic lung), target gentle ventilation
• Consider inhaled nitric oxide (iNO) for PPHN
• Sedation/analgesia to reduce pulmonary vascular resistance (PVR) spikes
• Avoid acidosis, hypothermia, and pain - all raise PVR

Key point: The exam tests that CDH surgery is delayed until physiologic stabilization; the operation is not an emergency in the same sense as a perforated viscus.

Ventilation strategy - 'gentle ventilation':

• Low PIP (typically ≤ 25–28 cmH2O) to avoid barotrauma to the hypoplastic contralateral lung
• PEEP 3–5 cmH2O to maintain FRC without overdistension
• Permissive hypercapnia: PaCO2 45–65 mmHg, pH ≥ 7.25 - accept higher CO2 rather than high pressures
• Rate: moderate (30–40) to allow expiration; avoid air trapping
• FiO2: titrate to preductal SpO2 90–95%; avoid hyperoxia

Reasoning:

• The ipsilateral lung is hypoplastic; the contralateral lung is the sole gas exchanger and is vulnerable to volutrauma and barotrauma
• High PIP raises intrathoracic pressure, reduces venous return, and can worsen hemodynamics
• Hyperventilation causes hypocarbia → cerebral vasoconstriction and is associated with worse outcomes
• Hyperoxia causes oxidative stress and does not improve PPHN

Intraoperative considerations:

• Avoid nitrous oxide (expands bowel, worsens lung compression)
• Maintain normothermia
• Minimal handling; avoid sudden PVR spikes (pain, suctioning, acidosis)

Key point: The exam tests the specific targets (permissive hypercapnia, low PIP, preductal SpO2) rather than generic 'ventilate gently.'

Differential for worsening hypoxemia with increased pre/postductal difference (PPHN crisis):

1. Pain or agitation → PVR spike
2. Acidosis or hypercapnia → PVR spike
3. Hypothermia
4. Pneumothorax (especially after CDH repair - check for it)
5. Atelectasis or mucus plugging
6. Sepsis
7. Recurrence of hernia / bowel in chest
8. Pulmonary hemorrhage

Immediate management:

• Increase sedation/analgesia (fentanyl bolus) - pain is a common trigger
• Optimize ventilation: correct acidosis, avoid hypercapnia, but do not hyperventilate
• Increase FiO2 transiently, then wean
• Consider iNO if not already on it; if on it, check delivery and consider escalation (milrinone, sildenafil)
• Chest radiograph to exclude pneumothorax
• Suction if mucus plugging suspected
• Echocardiogram to reassess RV pressure and function
• Avoid systemic hypotension - maintain systemic pressure to reduce right-to-left shunt

Key point: The exam tests a structured approach: identify triggers (pain, acidosis, hypothermia, pneumothorax), treat the cause, and use pulmonary vasodilators judiciously. Do not reflexively hyperventilate.