Newborns' Sao2 Levels: Achieving Stability After Birth

The time it takes for a newborn's Sao2 to reach 90 after birth depends on several factors, including the mode of delivery, birth weight, and gestational age. In a study of 204 healthy newborns, the median time to reach an SpO2 of 90% was 6.5 minutes, with a range of 2 to 10 minutes. The mode of delivery was found to have a significant impact, with newborns born via cesarean section taking longer to reach SpO2 of 90% than those born vaginally. In another study, the median SpO2 at 5 minutes of age was found to be 90% for vaginally delivered infants and 87% for those delivered by cesarean section. The reference range for SpO2 in healthy term newborns within the first 10 minutes after birth is 66% at 1 minute, 78% at 3 minutes, 89% at 5 minutes, 95% at 8 minutes, and 96% at 10 minutes.

Oxygen saturation in healthy infants immediately after birth

Immediately after birth, a newborn's oxygen saturation levels are relatively low compared to the levels of a newborn infant. In the minutes after birth, the arterial oxygen saturation rises from around 50-60% to 90-95%.

In one study, 50 healthy vaginally delivered newborn infants were examined in the second minute of life. The mean preductal oxygen saturation was 73% and 67% in the postductal region. Oxygen saturation levels of >95% were reached after 12 minutes preductally and after 14 minutes postductally.

Another study found that the median oxygen saturation at 1 minute was 63% and there was a gradual rise in oxygen saturation with time, with a median saturation of 90% at 5 minutes.

Delayed cord clamping has been found to positively influence the fetal-to-neonatal transition, with oxygen saturation plateauing significantly earlier to values of 85-90% than in babies with immediate cord clamping.

The reference range for oxygen saturation in the first 10 minutes following birth is as follows:

• 66% at 1 minute of age
• 78% at 3 minutes of age
• 89% by 5 minutes of age
• 95% by 8 minutes of age
• 96% by 10 minutes of age

Oxygen saturation trends in the first 10 minutes after birth

Immediately after birth, a newborn's arterial oxygen saturation rises from around 50-60% to 90-95%. The following trends have been observed in the first 10 minutes after birth:

First Minute After Birth

• The median pre-ductal oxygen saturation (SpO2) for all infants (term and preterm) is 66%.
• The median SpO2 for preterm infants is 62% compared to 68% for term infants.
• The median SpO2 for infants born via Caesarean section is 54% compared to 67% for vaginal births.

Third Minute After Birth

• The median pre-ductal SpO2 for all infants is 78%.
• The median SpO2 for preterm infants is 76% compared to 81% for term infants.
• The median SpO2 for infants born via Caesarean section is 67% compared to 80% for vaginal births.

Fifth Minute After Birth

• The median pre-ductal SpO2 for all infants is 89%.
• The median SpO2 for preterm infants is 86% compared to 92% for term infants.
• The median SpO2 for infants born via Caesarean section is 85% compared to 92% for vaginal births.

Eighth Minute After Birth

The median SpO2 for all infants is 95%.

Tenth Minute After Birth

• The median SpO2 for all infants is 96%.
• The median SpO2 for preterm infants is 94% compared to 97% for term infants.
• The median SpO2 for infants born via Caesarean section is 94% compared to 96% for vaginal births.

It is important to note that these values are for newborns who had early cord clamping. Delayed cord clamping can result in earlier plateauing of oxygen saturation and fewer episodes of brady-or-tachycardia in the first minutes after birth.

Oxygen saturation in newborns delivered via C-section vs vaginal birth

In the minutes after birth, a newborn's arterial oxygen saturation rises from around 50-60% to 90-95%.

A study by Rashi Bhargava et al. found that newborns delivered vaginally had significantly higher peripheral oxygen saturation (SpO2) levels than those delivered via elective C-section within the first 30 minutes of life. The mean SpO2 was 85.4%, 90.8%, 94.1%, 95.7%, 96.7%, and 97.4% at 5, 10, 15, 20, 25, and 30 minutes, respectively, after birth for all newborns in the study. However, newborns delivered vaginally had a mean SpO2 of 90.8% at 10 minutes, compared to 88.5% for those delivered via C-section. Additionally, newborns delivered vaginally reached a SpO2 of greater than 90% faster, taking an average of 9.13 minutes compared to 12.31 minutes for those delivered via C-section.

Another study by Berndt Urlesberger et al. found that newborns delivered via C-section had significantly lower SpO2 values from 4 to 8 minutes after birth compared to those delivered vaginally. However, there was no difference in regional oxygen saturation of the brain (rSO2brain) between the two groups.

Furthermore, a study by Inmaculada Lara-Cantón and Máximo Vento found that infants born by C-section had lower oxygen saturation levels compared to those born vaginally in the first 5 minutes after birth. Specifically, infants born via C-section had a median SpO2 of 54% at 1 minute and 67% at 3 minutes, compared to 67% and 80%, respectively, for those born vaginally.

Overall, these studies suggest that newborns delivered vaginally may have higher oxygen saturation levels in the first few minutes after birth compared to those delivered via C-section. However, more research is needed to confirm these findings and understand the underlying mechanisms.

The role of pulse oximetry in monitoring newborn oxygen saturation

Pulse oximetry is a non-invasive method of measuring the oxygen saturation of haemoglobin. It is a critical tool in determining the need for oxygen supplementation in sick newborns. It has become standard practice to monitor arterial oxygen saturation (SpO2) and heart rate (HR) using pulse oximetry to objectively guide resuscitation.

Pulse oximetry works by measuring SpO2 continuously and non-invasively, without the need for calibration. It is based on the red and infrared light absorption characteristics of oxygenated and deoxygenated haemoglobin. A sensor is placed around the baby's hand or foot, and two light-emitting diodes send red and infrared light through to a photodetector on the other side. The changes in absorption during the arterial pulsatile flow and non-pulsatile component of the signal are analysed to estimate SpO2.

Pulse oximetry can be successfully used to monitor newborn oxygen saturation in the first few minutes after birth. However, it is important to note that motion artefacts, vernix, low perfusion, oedema, high ambient light, and other factors can affect the accuracy of readings. The success rate of obtaining SpO2 measurements improves with newer oximeters and as the baby gets older, with a success rate of between 63% and 100% by 5 minutes after birth.

The placement of the oximeter sensor is important. Readings are obtained fastest from the right hand, likely due to better perfusion, higher blood pressure, and oxygenation in preductal vessels. Preductal readings are significantly higher than postductal readings in the first few minutes after birth. By 17 minutes after birth, there is no longer a significant difference between preductal and postductal measurements.

Pulse oximetry can be used to measure SpO2 and guide interventions during neonatal transition. For example, Deckardt et al. used SpO2 readings at 5 minutes after birth to determine whether infants should receive continuous positive airway pressure (CPAP) with a mask and 100% oxygen. Kopotic and Lindner studied 50 infants at risk for respiratory failure and managed them with or without oximetry, finding that those managed with oximetry were less likely to be admitted to the special care nursery.

In summary, pulse oximetry plays a crucial role in monitoring newborn oxygen saturation and guiding interventions during neonatal transition. It provides a non-invasive, continuous, and reliable method for measuring SpO2, which can help improve short-term outcomes such as admission to the nursery and the use of oxygen or CPAP. However, more research is needed to define normoxia and how to interpret and apply SpO2 readings to improve long-term outcomes.

Factors influencing newborn oxygen saturation adaptation

Newborns experience a rapid increase in oxygen saturation levels in the minutes after birth, rising from around 50-60% to 90-95%. This rise is driven by various factors, including physiological changes, clinical interventions, and environmental conditions. Here are some key factors influencing newborn oxygen saturation adaptation:

Physiological Changes

• Initial Respiratory Efforts: The first breaths after birth generate negative trans-thoracic pressures, pushing fluid from the airways into the lung interstitium. This facilitates lung aeration, blood oxygenation, and pulmonary artery vasodilation, optimizing gas exchange and oxygen saturation.
• Cardiac Shunting: The fetal circulation, which includes intra-cardiac (foramen ovale) and extra-cardiac (ductus arteriosus) shunting, switches to a parallel pulmonary and systemic circulation after birth. This change ensures that oxygenated blood reaches vital organs.
• Placental Blood Flow: Delayed cord clamping preserves blood flow through the placenta, increasing ventricular preload and contributing to a more stable hemodynamic transition.
• Oxygen-Hemoglobin Affinity: Hemoglobin plays a crucial role in oxygen transport and regulation. Its affinity for oxygen increases as partial pressure increases, allowing more oxygen binding until saturation.
• Pulmonary Vasodilation: Oxygen acts as a potent vasodilator, aiding in the decrease in pulmonary vascular resistance at birth. This facilitates the transition to pulmonary circulation and optimizes oxygen saturation.

Clinical Interventions

• Resuscitation Practices: The American Heart Association guidelines recommend using room air (21% oxygen) for term infants during resuscitation and titrating oxygen levels to match uncompromised term infants. For preterm infants, targeting a higher saturation range may be safer.
• Delayed Cord Clamping: Delayed cord clamping positively influences the fetal-to-neonatal transition, leading to earlier oxygen saturation plateauing and reduced episodes of bradycardia or tachycardia.
• Skin-to-Skin Contact: Immediate skin-to-skin contact after birth can influence oxygen saturation levels, with studies showing lower heart rates in these newborns compared to those without immediate contact.
• Mode of Delivery: Infants born via Caesarean section tend to have lower oxygen saturation levels in the first few minutes after birth compared to those born vaginally.

Environmental Conditions

• Altitude: Newborns born at higher altitudes may have different oxygen saturation norms. Studies at moderate altitudes of 1800 meters suggest that a saturation range of 89%-97% is suitable for well-term and preterm infants within 24 hours.
• Temperature: Oxygen is crucial for thermoregulation, and hypoxia can suppress non-shivering thermogenesis, making it challenging for infants to maintain body temperature in colder environments.

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