Pulse Oximetry in the diagnosis of critical congenital cardiac disease

Overview

• Routine pulse oximetry screening recommended for all newborns.
• Primary goal: Detect unsuspected critical cyanotic congenital heart disease (CCHD).
• Detects respiratory disorders and primary pulmonary hypertension.
• Overcomes visual limitations; clinical cyanosis easily missed due to dark skin color, poor lighting, or anemia.
• Detects milder forms of hypoxia invisible to naked eye.
• Normal oxygen saturation >98% in infants.
• Threshold for classifying desaturation <95% in room air.

Target Lesions Detected

Category	Specific Critical Congenital Heart Lesions
Duct-Dependent Systemic Circulation	Hypoplastic left heart syndrome (HLHS) Critical aortic valve stenosis Severe coarctation of the aorta Interrupted aortic arch
Duct-Dependent Pulmonary Circulation / Right-Sided Lesions	Pulmonary atresia with intact ventricular septum (PA/IVS) Critical pulmonary stenosis Severe Tetralogy of Fallot (TOF) Tricuspid atresia
Mixing Lesions / Transposition	D-Transposition of the great arteries (D-TGA) (especially at risk for restrictive atrial septum)
Severe Venous/Valvular Lesions	Obstructed total anomalous pulmonary venous return (TAPVR) Congenital mitral and tricuspid valve regurgitation Neonatal Ebstein anomaly

Screening Protocol

• Timing: Performed between 24 and 48 hours of life.
• Executed before discharge in asymptomatic newborns.
• Measurements required: Pre-ductal (right hand) and post-ductal (either foot).

Pulse Oximetry Screening Algorithm

Result Category	Pulse Oximetry Criteria	Clinical Action
Pass	$\ge$ 95% in right hand or foot AND $\le$ 3% difference between right hand and foot	Screen passed; routine care.
Fail (Immediate)	< 90% in either right hand or foot	Urgent echocardiography indicated.
Equivocal	90–94% in hand or foot OR > 3% difference between right hand and foot	Repeat screen once in 1 hour.
Fail (Delayed)	90–94% OR > 3% difference after third consecutive screen	Urgent echocardiography indicated.

flowchart TD
    A[Perform Pulse Oximetry <br>at 24-48 hours of life] --> B{Initial SpO2 Measurement<br/>Right Hand & Either Foot}
    B -->|SpO2 < 90% in <br>RH or Foot| C[FAIL Screen]
    B -->|SpO2 >= 95% in <br>RH or Foot AND<br/>Difference <= 3%| D[PASS Screen]
    B -->|SpO2 90-94% in <br>RH and Foot OR<br/>Difference > 3%| E[Repeat Screen in 1 Hour]
    E --> F{Second SpO2 Measurement}
    F -->|SpO2 < 90% in <br>RH or Foot| C
    F -->|SpO2 >= 95% in <br>RH or Foot AND<br/>Difference <= 3%| D
    F -->|SpO2 90-94% in <br>RH and Foot OR<br/>Difference > 3%| G[Repeat Screen in 1 Hour]
    G --> H{Third SpO2 Measurement}
    H -->|SpO2 < 90% in <br>RH or Foot| C
    H -->|SpO2 >= 95% in <br>RH or Foot AND<br/>Difference <= 3%| D
    H -->|SpO2 90-94% in <br>RH and Foot OR<br/>Difference > 3%| C
    C --> I[Urgent Clinical Evaluation<br> & Echocardiogram]
    D --> J[Routine Neonatal Care]

Follow-up on Positive Screen

• Urgent echocardiography required.
• Careful reexamination of peripheral pulses.
• Four-extremity blood pressure measurements.
• Detailed cardiac auscultation.

Diagnostic Interpretation of Saturation Discrepancies

Differential Cyanosis

• Defined as lower extremity saturation lower than right arm saturation (e.g., right wrist 97%, left foot 72%).
• Indicates right-to-left shunting across patent ductus arteriosus.
• Associated lesions: Coarctation of the aorta, interrupted aortic arch, persistent pulmonary hypertension.

Reverse Differential Cyanosis

• Defined as upper extremity oxygen saturation lower than lower extremity saturation.
• Seen in d-transposition of the great arteries combined with either coarctation of the aorta or persistent pulmonary hypertension of the newborn.

Technical Limitations

• Accuracy optimal when blood oxygen saturation remains between 90% and 100%.
• Accuracy decreases when blood oxygen saturation drops to 80–90%.
• Devices inaccurate when saturation falls below 40%.