Preductal measurement
Preductal SpO₂ is measured on the right hand or right wrist. It reflects blood before ductal mixing and is the preferred site for assessing upper-body oxygenation in newborns.
Postductal measurement
Postductal SpO₂ is measured on either foot. It reflects blood after potential ductal shunting and can fall lower when right-to-left flow crosses the ductus arteriosus.
Why the difference matters
A persistent preductal-to-postductal gradient can point toward PPHN physiology, pulmonary vascular resistance, parenchymal lung disease, or congenital heart disease that needs escalation.
Clinical concept
What is pre- and post-ductal oxygenation?
In newborns, the ductus arteriosus can allow blood to bypass the lungs during fetal life. After birth, pulmonary vascular resistance should fall and pulmonary blood flow should rise. If pulmonary vascular resistance remains high, blood can continue to shunt through the ductus, causing the oxygen saturation in the foot to run lower than the right hand.
This is why the right hand matters: it is considered preductal. The foot is postductal. A sustained difference between those two values can become an important clue in suspected PPHN, delayed transition, parenchymal lung disease, or congenital heart disease evaluation.
Correct probe placement
- Preductal: right hand or right wrist.
- Postductal: either foot.
- Avoid: using the left hand as the “preductal” site because anatomy can make interpretation less clean.
- Always verify: waveform quality, perfusion, motion artifact, probe size, and sensor adhesion.
Interpretation table
How much difference is concerning?
| Finding | Difference | Clinical meaning |
|---|---|---|
| Normal / expected | ≤ 3% SpO₂ | Usually no significant ductal gradient after transition, assuming reliable waveform and correct probe placement. |
| Borderline difference | 4–5% SpO₂ | Repeat, verify probe placement, check perfusion, and interpret with age after birth and clinical status. |
| Significant gradient | > 5% SpO₂ | Concern for ductal shunting or PPHN physiology, especially if persistent or paired with respiratory distress. |
| Reverse differential | Postductal higher | Unusual pattern that can suggest complex cardiac physiology and should prompt urgent evaluation. |
When to worry about PPHN physiology
A preductal saturation that remains meaningfully higher than the postductal saturation suggests right-to-left ductal shunting. In the right clinical picture, that can support concern for persistent pulmonary hypertension of the newborn. This is especially important when there is respiratory distress, high oxygen need, labile saturations, meconium aspiration, sepsis, pneumonia, congenital diaphragmatic hernia, or severe parenchymal lung disease.
Pre/post-ductal monitoring does not diagnose PPHN by itself. It helps decide when to escalate, when to seek echocardiography, and when to integrate other data such as oxygenation index, blood gases, lactate, blood pressure, perfusion, and ventilator response.
Common pitfalls
- • Comparing right hand to left hand instead of right hand to foot.
- • Treating poor waveform or cold extremities as true ductal shunting.
- • Forgetting that transitional differences can occur early after birth.
- • Assuming equal saturations exclude disease when both values are low.
- • Ignoring reverse differential cyanosis when postductal saturation is higher.
Practical bedside approach
- • Confirm right-hand preductal placement and foot postductal placement.
- • Check waveform quality and perfusion before interpreting the gradient.
- • Compare SpO₂ difference and PaO₂ difference when arterial samples are available.
- • Use the Pre/Post-Ductal Analyzer to frame the pattern.
- • Correlate with cord gases, capillary gases, and neonatal VBGs when acid-base status matters.
Neonatal tool cluster
Use the related neonatal calculators
Pre/post-ductal oxygenation is only one piece of the newborn respiratory picture. These PulmTools calculators are built to work together.
Pre/Post-Ductal Analyzer
Compare preductal and postductal SpO₂ / PaO₂, detect ductal shunting patterns, and review CCHD screening logic.
Open →Cord Gas Analyzer
Interpret umbilical arterial and venous cord gases with acidemia severity and sample reliability checks.
Open →CBG Analyzer
Interpret capillary gases with perfusion-aware confidence scoring and capillary PO₂ guardrails.
Open →Neo/Peds VBG Analyzer
Interpret neonatal and pediatric venous gases with age-aware acid-base framing and venous PO₂ warnings.
Open →Neo/Peds Oxygenation Reference
Review target ranges, oxygen devices, escalation pathways, and safety considerations.
Open reference →HFNC / CPAP Reference
Pair oxygenation findings with noninvasive respiratory support and escalation guidance.
Open reference →Neo/Peds Ventilation Reference
Review neonatal and pediatric ventilator settings, PEEP, rates, and lung-protective principles.
Open reference →