During the first few minutes of life, oxygen saturation (saturation by pulse oximetry, SpO₂) increases from intrapartum levels of 30–40%.¹ In algorithms for neonatal resuscitation published by the International Liaison Committee for Resuscitation,² European Resuscitation Council³ and Australian Resuscitation Council,⁴ clinical assessment of an infant’s colour (a measure of oxygenation) and heart rate are used as major action points. However, studies have shown that clinical assessment of colour during neonatal transition is unreliable.^5,6 O’Donnell et al⁶ showed that the SpO₂ at which observers perceived infants to be pink varied widely, ranging from 10% to 100%. Assessing colour is difficult and therefore is a poor proxy for tissue oxygenation during the first few minutes of life.

Kattwinkel⁷ suggested pulse oximetry may help achieve normoxia in the delivery room. The American Heart Association⁸ suggests that “administration of a variable concentration of oxygen guided by pulse oximetry may improve the ability to achieve normoxia more quickly”. Although “normoxia” and an acceptable time to achieve this during neonatal transition have not been defined, Leone and Finer⁹ advocate a target “SpO₂ of 85 to 90% by three minutes after birth for all infants except in special circumstances”—for example, diaphragmatic hernia or cyanotic congenital heart disease. International surveys show that oximetry is increasingly used during neonatal resuscitation.^10,11

To date, there are no evidence-based guidelines for using oximetry to measure an infant’s SpO₂ and to guide interventions during neonatal transition after birth. We reviewed the literature to evaluate the evidence on the use of SpO₂ measurements immediately after birth.

HOW DOES PULSE OXIMETRY WORK?

Pulse oximetry measures SpO₂ continuously and non-invasively, without the need for calibration, and correlates closely with arterial oxygen saturation.¹² Pulse oximetry is based on the red and infrared light-absorption characteristics of oxygenated and deoxygenated haemoglobin. A sensor is placed around a 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. SpO₂ is estimated from the transmission of light through the pulsatile tissue bed. With each heartbeat, there is a surge of arterial blood that momentarily increases arterial blood volume. This results in more light absorption during surges. As peaks occur with each heartbeat, heart rate can also be measured.

CAN SPO₂ BE SUCCESSFULLY MEASURED IN THE MINUTES AFTER BIRTH?

Seven studies reported between 20% and 100% success in obtaining SpO₂ measurements by 1 min after birth.^5,13–18 By 5 min, the success rate improved to between 63% and 100%.^{13,15–17,19–23} The most common reason for failing to obtain a measurement was motion artefact^{5,16,18–20,24}; others were the presence of vernix,²⁵ low perfusion,²⁵ oedema,¹⁵ high ambient light,^14,24 large infants,²⁴ cracked and wrinkled skin,¹⁵ or acrocyanosis.¹⁵ Artefacts occurred less often in more recent studies where Masimo signal extraction technology (SET) was used.^18,25

WHERE SHOULD THE OXIMETER SENSOR BE APPLIED?

In early studies, investigators placed the sensor over the right Achilles tendon,^20,25–27 the forefoot¹⁹ or midfoot.^22,28 Later studies found that measurements were obtained fastest from the right hand,¹⁵ probably owing to better perfusion, higher blood pressure and oxygenation in preductal vessels.^14,29 Preductal readings were significantly higher than postductal readings soon after birth (p<0.05).^5,15,22 By 17 min after birth, there was no longer a significant difference between preductal and postductal measurements (p<0.05).^5,15,22

HOW QUICKLY CAN AN SPO₂ READING BE OBTAINED?

A sensor can be applied to a baby within 15–20 s of birth,^18,21 with the first data obtained at about 50 s after birth.^15,18,21 No studies obtained SpO₂ data on most infants before 1 min after birth.^14,25,26,29 When the Masimo sensor and monitor were used, readings were obtained faster than when the sensor was applied to the infant before connecting it to the oximeter.²¹

HOW DO SPO₂ READINGS CHANGE IN THE FIRST FEW MINUTES AFTER BIRTH?

Some studies report the range of SpO₂ at 1, 5 or 10 min (tables 1 and 2); others report the time taken to reach a predetermined SpO₂ (table 3). These studies show increases in SpO₂ from about 60% at 1 min, but the levels vary widely, with some infants taking >10 min to exceed 90%. Therefore, it may not be appropriate to identify specific SpO₂ levels at certain times after birth, which can be used as a trigger to alter an infant’s treatment.

DOES THE TYPE OF OXIMETER ALTER THE SPO₂ RESULTS?

Early oximeters had motion artefact.^{5,16,18–20,24} This has been improved in newer oximeters.^25,33 To determine whether the newer oximeters were more reliable than earlier models in the delivery room, Kopotic compared the Masimo SET to the Nellcor Oxismart, with sensors placed on each foot, in 15 newborns of <30 weeks’ gestation.²⁵ The Masimo SET provided data for 350 of 362 (96%) min, and the Oxismart provided data for 212 of 362 min (59%; p = 0.0014).²⁵ Leone and Finer⁹ recommended that oximeters used during neonatal resuscitation should have “minimal averaging time for the SpO₂ values coupled with maximum sensitivity”. The combination of these features allows rapid detection of changes in SpO₂ and improved SpO₂ measurement during periods of low perfusion.³⁴

DOES THE TYPE OF DELIVERY ALTER THE SPO₂ AFTER BIRTH?

Harris et al²⁰ found, using an early generation oximeter, that SpO₂ was much lower in 44 term elective caesarean-section deliveries, when compared with 32 term infants delivered vaginally. The mean (standard error, SEM) SpO₂ at 1 min was 46% (3%) in the caesarean group and 61% (5%) in the vaginal delivery group (p<0.05), but by 5 min there was no significant difference. They postulated that the difference was due to the increased amount of lung fluid after caesarean section. Kamlin et al¹⁸ found that 107 term infants born by elective caesarean section took on average 2 min longer to reach an SpO₂ >90% than 68 infants born by spontaneous vaginal delivery. Rabi et al²⁹ found a similar difference in a cohort of 115 infants. In infants of >34 weeks’ gestation, the median (interquartile range, IQR) for vaginal births at 5 min was 87% (80–95%) and that for caesarean delivery was 81% (75–83%).²⁹ In contrast, others found no significant difference in SpO₂ measurements in infants delivered vaginally or by caesarean section, regardless of the presence or type of anaesthesia.^5,14,24

DOES RESUSCITATION WITH AIR OR OXYGEN AFFECT SPO₂ AFTER BIRTH?

Table 4 summarises trials comparing SpO₂ measurements at 1, 3 and 5 min in infants with asphyxia randomised to receive air or 100% oxygen during resuscitation. In the Resair 2 study, which enrolled infants weighing >999 g with apnoea and bradycardia at birth, there were no significant differences in time to reach an SpO₂ of 75%. The median (95% confidence interval) time to reach an SpO₂ of 75% was 1.5 (1.4 to 1.6) min in the group receiving air versus 2.5 (1.9 to 3.1) min in the group receiving oxygen (p = 0.27).³² In this study, the resuscitators were aware of the gas used, whereas Vento et al³¹ blinded resuscitators to the type of gas used to resuscitate infants with asphyxia. He found no significant difference in time to reach an SpO₂ >90% between the two groups with asphyxia. The striking result of these studies is that resuscitating with air or 100% oxygen had little effect on the change in SpO₂ in the first 10 min after birth.

DOES ALTITUDE AFFECT SPO₂ AFTER BIRTH?

Gonzales and Salirrosas²⁸ showed that SpO₂ was significantly higher in infants born at sea level (Lima 150 m) than in infants born at a higher altitude (Cerro de Pasco 4340 m) from 1 min to 24 h after birth (p<0.01).

DOES GESTATION AFFECT SPO₂?

There are two reports of SpO₂ measurements in premature infants after birth. In Kopotic and Lindner’s²⁵ study of 15 infants born at 24–29 weeks’ gestation, the SpO₂ was ⩾80% by 4.4 (1.9–40) min (median (range)). In the study by Kamlin et al¹⁸ on infants not receiving resuscitation, the time to reach an SpO₂ >90% was significantly longer in 54 preterm infants at 6.5 (4.9–9.8) min (median (IQR)) than in 121 term infants at 4.7 (3.3–6.4) min (median (IQR)) (p<0.001). Other studies including premature infants did not report SpO₂ for different gestational ages.^14,32

CAN OXIMETRY BE USED TO MEASURE THE EFFECT OF RESUSCITATION PRACTICES?

Oximetry has been used to measure the effect of clinical interventions, such as oropharyngeal suction and endotracheal intubation during neonatal transition. Three controlled studies show that suctioning does seem to have a negative effect on oxygenation.^13,23,30 O’Donnell et al³⁶ measured the effects of attempted endotracheal intubation on SpO₂ in the delivery room, and SpO₂ often fell during intubation attempts.

COULD OXIMETRY BE USED IN THE DELIVERY ROOM TO IMPROVE OUTCOMES?

There are two studies that evaluate the use of oximetry to guide interventions during neonatal transition. Deckardt et al¹⁹ used SpO₂ readings at 5 min after birth to determine whether infants should receive continuous positive airway pressure (CPAP) with a mask and 100% oxygen. CPAP was used only if the SpO₂ was <80% at 5 min and stopped once the SpO₂ reached 90%. Kopotic and Lindner²⁵ studied 50 infants at risk for respiratory failure; 25 infants were managed without oximetry and compared with 25 managed with oximetry. Infants managed with oximetry were less likely to be admitted to the special care nursery (32% v 52%; p = 0.04). They also observed the effect of oximetry during resuscitation in 15 infants of <30 weeks’ gestation. Initial respiratory care was based on the infant’s clinical state and oximetry measurements. Oxygen was started at 100% and adjusted to achieve an SpO₂ between 80% and 92%.²⁵ The authors claim that by using pulse oximetry they were able to reduce the fraction of inspired oxygen (FiO₂) from 1.0 to, on average, 0.40. The studies by Kopotic and Deckardt, although non-blinded and non–randomised, suggest that oximetry can improve short-term outcomes—for example, admission to nursery, the use of oxygen or CPAP. We could find no reports on whether the use of SpO₂ measurements immediately after birth alters long-term outcomes.

CONCLUSION

Before oximetry is advocated for routine use in the delivery room, more research is needed to define normoxia, and more importantly, how to interpret and apply SpO₂ readings to clinical practice to improve short-term and long-term outcomes.