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

$Pa{O}_2$ Level (mm Hg)	Likely Etiology	Key Notes
> 300	Healthy newborn	Normal response.
150 - 300	Noncardiac etiologies (Pulmonary disease, CNS disorders, Methemoglobinemia)	Not 100% confirmative; rare cyanotic CHD cases achieve >150 mm Hg via favorable intracardiac streaming.
100 - 150	Cyanotic CHD (mixing lesions with increased pulmonary blood flow) or PPHN	-.
< 100	Cyanotic CHD (decreased pulmonary blood flow)	Typical of severe right ventricular outflow tract obstruction.

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

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