Pre and Post Ductal Oxygen Saturation Measurements in Newborns
Primary Clinical Significance
Pre-ductal and post-ductal oxygen saturation measurements are essential for detecting critical congenital heart disease (CCHD), guiding oxygen therapy during resuscitation, and identifying other serious cardiopulmonary conditions in newborns. 1
Key Anatomical Distinction
Measurement Sites
- Pre-ductal: Right upper extremity (wrist or medial palm) - reflects oxygen saturation before the ductus arteriosus 2
- Post-ductal: Either lower extremity (foot) - reflects oxygen saturation after the ductus arteriosus 3
This anatomical difference is critical because in ductal-dependent cardiac lesions, there can be significant differences between pre- and post-ductal saturations 1.
Clinical Applications
1. CCHD Screening (Primary Application)
Screening should be performed at approximately 24 hours of life using simultaneous pre- and post-ductal measurements. 1, 4
Screening Criteria for Abnormal Results:
- Oxygen saturation <95% in both pre-ductal and post-ductal sites 1
- OR >3% difference between pre- and post-ductal measurements 5
- OR Any single measurement <90% 1
Critical Management Points:
- Failed screening requires immediate echocardiography to rule out cardiac causes 1
- Screening must be performed on room air to avoid false negatives 1
- One retest is permitted if initial screen is abnormal 1
- CCHD screening has decreased early infant deaths from CCHD by 33% 1
2. Resuscitation Guidance
During neonatal resuscitation, oxygen therapy should be titrated to achieve pre-ductal saturations matching the interquartile range of healthy term infants. 2
Target Saturations by Time After Birth:
- Normal healthy term infants take 12-14 minutes to reach SpO2 ≥95% 3
- At 1 minute: median 63% (IQR: 53%-68%) 6
- At 5 minutes: median 90% (IQR: 79%-91%) 6
- Many healthy newborns have SpO2 <90% during the first 5 minutes of life 6
Resuscitation Oxygen Recommendations:
- Term/late-preterm (≥35 weeks): Start with 21% oxygen (room air) 2
- Preterm (<35 weeks): Start with 21-30% oxygen 2
- 100% oxygen is NOT recommended for term/late-preterm infants (Class 3: Harm) 2
- Titrate oxygen to achieve pre-ductal saturations approximating healthy term infant ranges 2
Critical caveat: If bradycardia (HR <60 bpm) persists after 90 seconds despite lower oxygen concentrations, increase to 100% oxygen until heart rate recovers 2.
3. Detection of Non-Cardiac Conditions
Most "false positive" CCHD screens actually identify clinically important non-cardiac conditions. 1
Conditions Detected:
- Persistent pulmonary hypertension of the newborn (PPHN) 5
- Respiratory distress syndrome (RDS) 5
- Pneumonia and other respiratory disorders 1
- Sepsis and other infections 1
In one study, positive predictive values were: CCHD 6.15%, RDS 40%, and PPHN 13.85% 5.
Normal Values at 24 Hours of Life
At approximately 24 hours after birth in asymptomatic newborns: 4
- Mean pre-ductal saturation: 98.29% (median 98%)
- Mean post-ductal saturation: 98.57% (median 99%)
- Post-ductal saturation was equal to or greater than pre-ductal in 78% of healthy newborns 4
This finding challenges the traditional assumption that pre-ductal saturations are always higher than post-ductal 4.
Preterm-Specific Considerations
Healthy preterm neonates achieve higher oxygen saturations faster than current NRP targets suggest. 7
- Median time to SpO2 >90%: 310 seconds (IQR: 235-400) 7
- Larger preterm infants (34-36 weeks) reach >90% faster than <34 weeks (290 vs 340 seconds) 7
- Vaginally delivered preterm infants reach >90% faster than cesarean-delivered (300 vs 360 seconds) 7
Technical Considerations
Optimal Probe Placement
- Pre-ductal monitoring requires right upper extremity placement to appropriately compare to published normative data 2
- Attaching the probe to the baby before connecting to the instrument may facilitate faster signal acquisition 2
Timing of Reliable Readings
- Modern neonatal pulse oximeters provide reliable readings within 1-2 minutes after birth 2
- In one study, first SpO2 reading was obtained within 60 seconds in only 53% of infants 6
- Mean time to first SpO2 in preterm infants: 167 ± 77 seconds 7
Critical Pitfalls to Avoid
Do not rule out CCHD based solely on normal screening - false negatives occur, and pulse oximetry sensitivity for CCHD is only 50-76% 1
Do not perform screening on supplemental oxygen - this creates false negatives 1
Do not delay echocardiography for failed screens - immediate cardiac imaging is essential 1
Do not assume pre-ductal is always higher than post-ductal - in 40% of healthy newborns at 24 hours, post-ductal equals or exceeds pre-ductal 4
Do not use 100% oxygen for initial resuscitation of term infants - this causes harm 2
Be aware that accuracy may vary with skin pigmentation - this requires further study 1
Special Populations
Newborns with suspected congenital heart disease or other malformations have not been adequately studied and should be managed according to guidelines for the wider population until specific data are available 2.