What’s the Difference between Pre-Ductal vs. Post-Ductal SpO2?

Pre-ductal and post-ductal SpO2 are arterial saturations. They refer to oxygen saturation levels in vessels that originate from the heart. The right hand of the infant is measured for pre-ductal and the foot for arterial post-ductal saturation. 

Specifically, pre- and post-SpO2 are oxygen saturation levels measured in blood vessels before and after the aortic duct orifice (hole produced in the aortic valve during blood flow). 

Screening oxygen saturation for newborns and infants could help detect critical cyanotic congenital heart disease (CCHD).

Pre- and Post-Ductal SpO2: The Process

An SpO2 rubber neonate wrap is positioned on the infant’s right hand to perform a pre-ductal reading and on either foot to perform a post-ductal reading. The practitioner should apply tape to hold the probe in a position to ensure accurate readings.

It’s crucial to wait until a stable, high-quality waveform is visible. If the signal readings are ≥ 95% and ≤ 2% difference, this is accepted as normal and constitutes no concerns.

Infant oxygen saturation screening enhances the detection of critical congenital heart disease (CCHD) by more than 92%. This procedure might not identify congenital heart defects, which don’t present with hypoxemia (lower than normal oxygen levels). However, it maximizes the detection rate of major congenital heart conditions.

Critical Recommendations

Every baby born in a hospital or admitted to the postnatal ward, whether due to maternal or neonatal reasons, must have their oxygen saturation levels checked 4–12 hours after birth. This is done by midwives or midwifery care assistants (MCAs).

Practitioners responsible for the routine neonatal examination must ensure they have recorded post-ductal oxygen saturation in the infant’s notes. The midwife should check the baby’s oxygen levels if they haven’t yet.

If the infant is over 12 hours old, this test is still valid in screening to check for congenital heart disease.

Healthy Infants with Low Oxygen Saturation

The neonatal team should discuss infants who appear healthy but have low oxygen saturation or a more than 2% pre- and post-ductal difference on pulse oximetry screening. They will triage review time and repeat the screening.

It’s appropriate for a neonatal team member to examine the patient thoroughly: look for any infection, difficulty in breathing, or CHD. If the readings have a difference of > 2%, they are regarded as abnormal and show right-to-left shunting.

If there isn’t shunting, pre-ductal and post-ductal oxygen saturation variation is ≤ 2%, and the infant is well, with 90%–94% saturations, NICU admission might not be required immediately. 

The neonatal team should repeat the SpO2 measurements on these infants after two hours. If the repeat results are normal and there aren’t other serious issues, usual care can proceed in the postnatal ward.

Suppose the results are abnormal or the infant is symptomatic, then the team should give the infant an urgent referral to admission to the NICU and neonatal unit to assess and investigate further or if treatment is necessary.

Post- and pre-ductal saturation is the base for vital congenital heart defect screening. If there is a difference of 4% or greater in pre-ductal versus post-ductal, the newborn must get an echo read to rule out any congenital heart defects.

Reasons and Benefits of Measuring Oxygen Saturation

Consider the reasons and benefits of measuring infant oxygen saturation to avoid mistakes in tests and treatments:

To Detect Critical Congenital Heart Disease (CCHD) 

Cardiovascular abnormalities are the top category of congenital malformations which affects 7–8 out of 1,000 newborn babies. Monitoring oxygen saturation is an understated way of improving the early discovery of CCHD in asymptomatic infants, consequently lessening the possibility of other health complications or even mortality.

Detecting CCHDs early expedites medical intervention, reducing the risk of severe or very severe onset symptoms. This approach leads to improved outcomes for those affected.

Detecting Asymptomatic CCHDs

Critical congenital heart disease symptoms aren’t always visible in the first few hours of the newborn’s life. This can extend even to the first few days after delivery due to the change from the circulation of a fetus to that of a normal child, which entails pressure variations between the heart and lungs chambers.

Practitioners might miss CCD in the regular clinical examination of infants after delivery. Most CCHDs arise due to an open ductus arteriosus, the hole that allows the blood to skip lung circulation in unborn infants. The infant’s health worsens quickly when the ductus remains closed after birth. If such infants are discharged with their condition unnoticed, they have a higher risk of being admitted again due to circulatory failure.

Detecting Other Conditions

Pulse oximetry is also an effective technique to detect other potentially ill infants who might otherwise appear healthy. Oxygen saturation measurements can be instrumental in detecting other severe non-cardiac conditions, such as pulmonary/respiratory disorders and infection, before the infant’s clinical condition worsens.

Timing of Pulse Oximetry

Timing may have an impact on the results of pulse oximetry screening. If the pediatric team carries out the examination early, the routine clinical examination will be less accurate as this changeover occurs. Routine neonatal examination and antenatal screening fail to identify up to 50% of CHD (false positive).

Other Factors

Several other factors can affect the pulse-oximetry-based diagnosis of congenital heart defects. The criteria for a pass or fail have been set based on research done in low-altitude regions.

Since oxygen saturations are usually lower at higher altitudes, applying a similar algorithm in infants at high altitudes may result in a higher rate of false positives. 

The false positivity rate is usually much lower in infants screened more than 24 hours after birth than in infants screened within 24 hours after delivery.

Recording and Interpreting Pre-ductal vs. Post-ductal SpO2 Results

The pediatric team should record the preductal and postductal results. The record should include the following:

• Date and time of screening
• The foot and hand used
• Results: pass or refer

95% or Higher

If oxygen saturation is 95% or higher, no more screening is required. If the infant examination is normal, no referral is required.

90%–94%

If oxygen saturation is between 90% and 94%, clinical assessment by the pediatric team is required.

Examination during clinical assessment includes the following:

• Femoral pulses
• Murmurs
• Preductal and post oxygen saturations evaluation

If the newborn has a regular clinical examination and the difference between post- and pre-ductal values is not more than 3%, a saturation screen is performed again after three hours.

It’s important to admit them into the special care nursery for further assessment if there are doubts about the infant’s health.

Investigations include the following:

• Four-limb blood pressure
• Chest x-ray
• Echo (echocardiogram); a normal ECG (electrocardiogram) might not exclude a cardiac lesion.

Should the repeat screening have saturation levels between 90% and 94%, it’s recommended to consult a pediatric specialist and perform further investigations.

After the consultant pediatrician has evaluated the infant and there is no other identifiable cause for hypoxemia, a referral to cardiology should be considered.

With an impressive 95% repeat saturation and intact femoral pulses, other assessments are unnecessary.

In cases where an infant is screened at 48 hours or more and has an oxygen saturation rate of less than 95%, they should be admitted to the special care nursery for further assessment since this usually suggests an underlying medical issue.

Below 90%

When oxygen saturation is below 90%, it calls for an urgent referral to the pediatric PIPER or team and admission to Special Care Nursery with further investigations and assessment that might include referral to cardiology. A pediatric team should consider a neonatal MET call.

Cardiology Referral

The team should follow any abnormal findings on the clinical examination (like abnormal readings from either foot) with a prompt referral for investigation and treatment.

Midwives should rule out CHD if the pediatric consultant’s assessment of pre- and postductal oxygen saturation gives no other sufficient reason for hypoxemia.

A referral to pediatric cardiology will be crucial to discuss:

• Further timing of an echo
• Transport to a care center for an echo
• Assessment by a cardiology

Potential Limitations of Pre-ductal And Post-ductal SpO2 Screening

A pulse oximeter is entirely safe and risk-free. Still, infants with a false-positive result might undergo unnecessary additional testing, such as echocardiography or a chest x-ray. They may be admitted or referred to a neonatal care unit.

This could lead to an unpleasant experience for the newborn, but most extra tests are typically non-invasive.

Some newborns may have undergone additional investigations and hospital stays because they tested positive in screening tests because their cultures were negative for sepsis.

However, pulse oximetry screening has fewer false-positive results than clinical exams. This is something to consider when evaluating the benefits and harms of pulse oximetry screening. The advantage of early screening outweighs any potential drawback by far.

Conclusion

The current study encourages pulse oximetry screening in newborns for detecting CCHDs. The study also encourages pulse oximetry in clinical examination and antenatal ultrasonography.

Early testing for CCHD using pulse oximetry comes with numerous advantages and cost-effectiveness. Any potential harm related to false positive tests isn’t serious.

Studies have revealed that pulse oximetry is a powerful tool in detecting CCHD, exhibiting a sensitivity rate as high as 76.5% and specificity of up to 99%, with an insignificant false-positive rate. This makes it a strong test.

Sometimes, pediatrics can fail to notice critical congenital heart disease and other life-threatening diseases identified through hypoxemia without pulse oximetry screening. This can result in potentially serious consequences.

Pulse oximetry is an easy, economical, non-invasive screening technique that can differentiate between a healthy life, a life with disability, or even death. This cost-effective approach ensures early detection and prevention of any complications.