Overview
Definition:
Critical Congenital Heart Disease (CCHD) refers to a range of serious heart defects present at birth that significantly impact a newborn's ability to oxygenate blood, requiring medical or surgical intervention shortly after birth
Pulse oximetry screening is a non-invasive bedside test to detect potential hypoxemia that may indicate CCHD.
Epidemiology:
CCHD affects approximately 1 in 125 live births worldwide
About 25% of these are considered critical, requiring intervention in the first year of life
The incidence can vary slightly by population and screening methods used
Early detection is crucial for improving outcomes.
Clinical Significance:
Early identification of CCHD through pulse oximetry screening allows for prompt diagnosis and management, significantly reducing morbidity and mortality
It is a cost-effective and highly sensitive method to identify infants at risk of severe hypoxemia and cardiovascular compromise, enabling timely referral to pediatric cardiology services.
Screening Protocol
Timing:
Screening should be performed after 24 hours of age, but before discharge from the nursery
If a baby is born prematurely (<37 weeks gestation) or screened before 24 hours, repeat screening is recommended before discharge
If the infant has been in the NICU, screening should occur before discharge.
Procedure:
Pulse oximetry is performed on the right hand (pre-ductal) and either the foot (post-ductal) or the other foot
The oxygen saturation (SpO2) is measured
Three consecutive readings are obtained over a period of 5 to 10 minutes
Readings should be taken when the infant is calm and stable, not crying excessively.
Passing Criteria:
A screen is considered negative (passed) if the SpO2 in both the right hand and foot is 95% or greater, and the difference between the upper and lower extremity readings is less than or equal to 3%.
Referral Criteria:
A screen is considered positive (failed) if the SpO2 in either the right hand or foot is less than 90%
A screen is also considered borderline (requires further evaluation) if the SpO2 is between 90-94% in either extremity, or if there is a difference of greater than 3% between upper and lower extremity readings, with at least one reading above 95%
Repeat screening may be performed after 1 hour if borderline.
Follow Up For Positive Screen
Immediate Steps:
If a screen is positive or borderline, a repeat pulse oximetry measurement should be performed after 1 hour
If the readings remain abnormal, the infant should undergo a full clinical assessment by a qualified healthcare provider
A detailed history and physical examination are essential.
Diagnostic Investigations:
The next step is a complete congenital echocardiogram (echo) to visualize the heart's structure and function, identify any defects, and assess their severity
Chest X-ray may be performed to assess for pulmonary pathology or cardiomegaly.
Cardiac Evaluation:
Referral to a pediatric cardiologist is mandatory for all infants with a positive or persistent borderline screen
The cardiologist will interpret the echocardiogram and determine the specific diagnosis and management plan
This may involve further investigations such as ECG or cardiac MRI if indicated.
Clinical Suspicion:
Even with a negative screen, if there is a high clinical suspicion for CCHD based on physical examination (e.g., murmur, poor feeding, tachypnea, poor weight gain), further cardiac evaluation should not be delayed.
Common Critical Congenital Heart Defects Detected
Aortic Stenosis:
Coarctation of the aorta (CoA) can lead to differential cyanosis and hypoperfusion distal to the coarctation
Pulse oximetry can detect lower saturation in the legs compared to the arms.
Pulmonary Atresia:
Pulmonary atresia with an intact ventricular septum requires a patent ductus arteriosus (PDA) for pulmonary blood flow
Neonatal hypoxemia may be detected if the PDA begins to close.
Transposition Of Great Arteries:
Transposition of the Great Arteries (TGA) is a cyanotic heart defect where systemic and pulmonary circulations are separated
Early hypoxemia is common if there is no mixing of blood.
Truncus Arteriosus:
Truncus Arteriosus involves a single great artery arising from the heart, supplying both pulmonary and systemic circulation
This often leads to significant shunting and hypoxemia.
Tetralogy Of Fallot:
Tetralogy of Fallot (TOF) is a complex cyanotic heart defect
Hypoxemia in TOF is often due to right ventricular outflow tract obstruction and VSD
"Tet spells" may indicate severe hypoxemia.
Tricuspid Atresia:
Tricuspid Atresia is a condition where the tricuspid valve fails to develop
Survival depends on shunting through an atrial septal defect (ASD) and a PDA for pulmonary blood flow.
Challenges And Limitations
False Positives:
False positive screens can occur due to factors like maternal smoking, respiratory distress syndrome, transient tachypnea of the newborn, or poor perfusion unrelated to CCHD
This can lead to parental anxiety and unnecessary investigations.
False Negatives:
False negative screens are a concern and can occur if the hypoxemia is intermittent, if the infant has significant ductal patency allowing for adequate oxygenation, or if other concurrent conditions mask the hypoxemia
Some CCHDs might not cause significant hypoxemia at the time of screening.
Intermittent Hypoxemia:
Some critical heart defects may present with intermittent hypoxemia or may not cause hypoxemia at the precise moment of screening, leading to a missed diagnosis
This highlights the importance of clinical vigilance alongside screening.
Accuracy In Specific Conditions:
Accuracy can be affected by conditions causing peripheral vasoconstriction (e.g., hypothermia, sepsis) or motion artifact
Proper technique and patient acclimatization are vital for reliable readings.
Key Points
Exam Focus:
Understand the screening timeline (post-24 hours), normal SpO2 thresholds (≥95%), difference limits (≤3%), and referral criteria (<90% or borderline)
Know the common CCHDs and their pathophysiology leading to hypoxemia.
Clinical Pearls:
Always perform screening before discharge
Be aware of the limitations and the potential for false negatives
Never rely solely on pulse oximetry
maintain high clinical suspicion for CCHD based on physical exam.
Common Mistakes:
Performing screening too early, not repeating readings if borderline, delaying echocardiogram after a positive screen, and overlooking clinical signs of CCHD in the presence of a negative screen.