Hyperoxia Test

Overview & Principle

• Distinguishes cyanotic Congenital Heart Disease (CHD) from primary pulmonary disease.
• Premise: Neonates with cyanotic CHD cannot significantly elevate arterial partial pressure of oxygen ($Pa{O}_2$) despite 100% oxygen administration.
• Infants with pulmonary disease increase intraalveolar $P{O}_2$, overcoming ventilation-perfusion mismatch and reversing hypoxia.

Methodology

• Administer 100% oxygen.
• Utilize oxygen hood.
• Avoid nasal cannula or face mask.
• Strict hood usage guarantees near 100% oxygen delivery, preventing false-positive results.

Interpretation of Results

Clinical Nuances & Differential Diagnosis

• Central Nervous System (CNS) Disorders: Hypoxia reverses completely with artificial ventilation.
• Transposition of the Great Arteries (TGA): Profound hypoxemia/cyanosis (saturations <70%) remains unresponsive to hyperoxia test.
• Management Implication: Lack of response to hyperoxia test in suspected TGA mandates immediate prostaglandin (PGE) initiation.

Related Fetal Variant: Maternal Hyperoxygenation (MH) Test

Purpose

• Evaluates fetal pulmonary vasoreactivity to oxygen.
• Predicts postnatal hemodynamic instability in high-risk CHD.

Procedure & Response

• Administer 100% oxygen to mother via non-rebreather face mask.
• Normal Fetal Response: $\ge$ 10% decrease in Doppler pulsatility indices of branch pulmonary arteries.
• TGA Application: Alterations in septum primum position or foramen ovale flow during MH predict postnatal need for balloon atrial septostomy (BAS).

Algorithmic Approach to the Hyperoxia Test

graph TD;
    A[Administer 100% Oxygen 
via Oxygen Hood] --> B{Measure Arterial PaO2};
    B -->|> 300 mm Hg| C[Healthy Newborn];
    B -->|150 - 300 mm Hg| D[Noncardiac Etiologies: 
Pulmonary disease, 
CNS disorders, 
Methemoglobinemia];
    B -->|100 - 150 mm Hg| E[Cyanotic CHD, 
Mixing Lesions, 
or PPHN];
    B -->|< 100 mm Hg| F[CHD with Decreased 
Pulmonary Blood Flow];

    D -.-> G[Note: May also include 
select Cyanotic CHDs 
with favorable streaming];
    E -.-> H[Note: Suspect TGA 
if unresponsive and 
profoundly hypoxemic - 
initiate PGE];
    F -.-> H;