Pulse Oximetry in the diagnosis of critical congenital cardiac disease

1. Introduction

Pulse oximetry screening is a non-invasive, bedside test used in asymptomatic newborns to detect subclinical hypoxemia, which may indicate duct-dependent "critical" congenital heart disease (CCHD). It aims to identify lesions before the ductus arteriosus closes and cardiovascular collapse occurs.

2. Screening Targets

• Primary Targets (7 defects):
  • Hypoplastic left heart syndrome (HLHS),
  • Pulmonary atresia,
  • Tetralogy of Fallot (TOF),
  • Total anomalous pulmonary venous return (TAPVR),
  • Transposition of the great arteries (TGA),
  • Tricuspid atresia,
  • Truncus arteriosus.
• Secondary Targets: Coarctation of the aorta, Interrupted aortic arch, and Ebstein’s anomaly.

3. Methodology

• Timing: Ideally performed between 24 and 48 hours of life. (Screening <24 hours increases false-positive rates due to transitional circulation).
• Pre-requisites: Infant should be quiet, alert, and off supplemental oxygen.
• Sites: 1. Pre-ductal: Right hand.
  2. Post-ductal: Either foot.
• Equipment: Use of "motion-tolerant" pulse oximeters validated for neonatal use.

4. Updated Screening Algorithm (AAP 2025)

A pass requires $Sp{O}_2\ge 95\mathrm{\%}$ in both extremities with $\le 3\mathrm{\%}$ difference.

1. PASS: * $Sp{O}_2\ge 95\mathrm{\%}$ in BOTH right hand and foot.

   • AND $\le 3\mathrm{\%}$ difference between sites.

2. IMMEDIATE FAIL:

   • $Sp{O}_2<90\mathrm{\%}$ in EITHER right hand or foot.

3. INDETERMINATE (Repeat after 1 hour):

   • $Sp{O}_2$ is $90-94\mathrm{\%}$ in either site OR $>3\mathrm{\%}$ difference between sites.
   • Action: Repeat screen once (Note: 2025 update reduces retests to one).
   • If the repeat screen does not meet "Pass" criteria, it is a FAIL.

5. Evaluation of Failed Screen

Infants failing the screen require urgent medical evaluation:

• Physical Exam: Assess for murmurs, femoral pulses, and respiratory distress.
• Differential Diagnosis: Sepsis, Pneumonia, Persistent Pulmonary Hypertension (PPHN), or CCHD.
• Definitive Test: Urgent Echocardiogram (read by a pediatric cardiologist) is mandatory if no non-cardiac cause for hypoxemia is identified.

6. Limitations

• Does not detect all CCHDs (e.g., Coarctation may pass if there is no significant ductal shunting).
• High false-positive rates in high-altitude regions.