Defining the Reference Range for Oxygen Saturation for Infants After Birth

DISCUSSION

This study reports how Spo₂ values changed in a large number of infants in the first 10 minutes after birth. We used a new-generation oximeter to reduce movement artifacts and studied only infants who received no DR interventions. Spo₂ increased steadily over time, requiring 8 minutes to exceed 90% in term infants. These data are comparable to those from other studies.^{3,5,–,10,12,17,25,–,27} Spo₂ is <60% in the fetus just before birth²⁸ and can decrease to 30% during labor.²⁹ For comparison, the 3rd percentile values at 1 minute and 5 minutes for all infants were 29% and 59%, respectively.

It is important to use the best technique to obtain a signal in the shortest possible time after birth. We used the method described by O'Donnell et al,²⁰ who showed that readings were obtained most quickly when the Masimo sensor was applied to the infant before being connected to the oximeter. We placed the sensor on the right hand or wrist of the infant because preductal Spo₂ is significantly higher than postductal Spo₂ soon after birth.^5,10,12,16 We used a Masimo pulse oximeter with 2-second averaging, set at maximal sensitivity, following the recommendation of Leone and Finer.²¹ This combination of settings improves Spo₂ measurements during periods of low perfusion.³⁰

One reason given for failure of Spo₂ measurements in the DR is motion artifacts.^{4,5,8,9,13,15} This is less when Masimo signal extraction technology is used.^9,31 We analyzed data only when there was a good plethysmographic wave and good signal quality. Therefore, our results are unlikely to be affected by artifacts. Different manufacturers use “fractional” or “functional” Spo₂ algorithms to calculate Spo₂. Thilo et al³² simultaneously placed oximeters with either a functional or fractional algorithm on 30 infants and found that the Nellcor oximeter (Nellcor Inc, Hayward, CA) (functional) read higher than the Ohmeda Biox 3700 oximeter (Ohmeda, Louisville, CO) (fractional) by a mean ± SD of 1.61 ± 2.69% (P < .001). There are no studies comparing oximeters in the DR. However, the differences between the Masimo oximeter (functional) and other oximeters that measure fractional Spo₂ are likely to be ∼2% and therefore not clinically important in this situation.

Our findings are consistent with those of Altuncu et al³ who, using a Nellcor oximeter, described the 10th, 25th, 50th, 75th, and 95th percentile ranges from 1 to 10 minutes for 200 newly born infants at >36 weeks of gestation. The median Spo₂ values at each minute were as follows: 1 minute, 71%; 2 minutes, 77%; 3 minutes, 83%; 4 minutes, 90%; 5 minutes, 92%; 6 minutes, 95%; 7 minutes, 96%; 8 minutes, 96%; 9 minutes, 97%; 10 minutes, 98%.³ The small differences with respect to our study could be explained by the slightly different techniques and different oximeters used.

There are reports of Spo₂ measurements with term infants just after birth but few with preterm infants. The median Spo₂ at 5 minutes for our preterm infants was 86%, compared with 92% for term infants (P < .001). Kamlin et al⁹ reported that the median Spo₂ at 5 minutes for preterm infants was 87%, which was significantly lower than the value for term infants of 90% (P < .001). Nuntnarumit and Rojnueangnit¹⁹ studied infants of <35 weeks who did not receive supplemental oxygen in the DR and reported slightly higher Spo₂ values over the first minutes and a shorter time to reach Spo₂ of 90% than we found in our study. The lower gestational age of the preterm infants in our study may explain the differences. In the observational study by Kopotic and Lindner³¹ of 15 infants born at 24 to 29 weeks of gestation, the mean time to reach Spo₂ of ≥80% was 4.4 minutes; however, their infants might have received oxygen therapy or other interventions.

Preterm infants are at most risk of harm from oxygen toxicity,^33,–,35 with the American Heart Association “cautioning the clinician about the use of excessive oxygen, especially in the premature infant.”³⁶ Our percentile values for Spo₂ in preterm infants after birth could assist clinicians in reducing the oxygen load³⁷ when supplemental oxygen treatment is used.

In the first 5 minutes after birth, infants born through cesarean section had significantly lower Spo₂ measurements than those delivered vaginally. This is consistent with the findings of Rabi et al¹⁴ and Harris et al.⁸ In contrast, other researchers found no significant differences between infants delivered vaginally or through cesarean section.^5,13,25 The latter studies had smaller samples and used older-generation pulse oximeters, which might explain their findings.

Spo₂ decreases with increasing altitude,⁷ and these percentile values might not apply to infants born at a high altitude. However, the magnitude of the changes with time is likely to be similar.

We have presented the data as smoothed percentile curves. These are used to show the distribution of measurements as they change according to some covariate, often age,²⁴ and are commonly used with anthropometric measurements to assess growth. The benefit of this method was that it allowed us to “capture” every measurement (61 650 Spo₂ data points), rather than “snapshots” of the data at each minute after birth. The use of percentiles to describe these data enables us to include all of the data collected every 2 seconds, rather than just values at each minute. If data were plotted at each minute, then an infant without data at that time would not be included in the chart; collecting data every 2 second enables more-accurate charting at each minute and for the 60 seconds between minute points. The use of medians, IQRs, and ranges does not give the same detail, with little information on one-half of the data in the upper and lower quartiles. Percentiles show the whole range of values. Percentile charts allow clinicians to choose Spo₂ levels above and below which they do not want the infant's Spo₂ values to go. Some clinicians may want to keep an infant's Spo₂ close to or above the median, others may not want the Spo₂ above the 90th percentile or below the 10th percentile, and others may chose the 25th percentile. Percentile charts allow clinicians to see the dynamic changes in Spo₂ values as they cross the percentiles. Pediatricians are very familiar with the concepts of percentile charts for growth and how they should be used and interpreted. We have presented percentile charts for all of the infants and for 3 gestational subgroups, that is, ≥37 weeks, 32 to 36 weeks, and <32 weeks. The difference in Spo₂ values between the preterm (<37 weeks) and term (≥37 weeks) infants is statistically significant; however, it is not likely to be clinically significant. There is a wide range of Spo₂ measurements in the first minutes after birth, and we recommend that clinicians consider using one of the charts when monitoring Spo₂ values during transition.

Infants in our study did not receive supplemental oxygen or respiratory support in the first 10 minutes after birth. In other locations, similar infants might have received supplemental oxygen or prophylactic continuous positive airway pressure therapy or intermittent positive pressure ventilation. At both hospitals during the study period, however, clinicians and not research team members were responsible for deciding whether to provide supplemental oxygen or respiratory support.

The aim of this study was to provide reference charts for Spo₂ measurements that clinicians could use during stabilization and resuscitation. This is especially important when treating extremely preterm infants at risk of hyperoxia.³⁸ The observational studies by Deckardt et al⁴ and Kopotic and Lindner³¹ suggested that using Spo₂ measurements in the DR was valuable in managing resuscitation. Recently, Finer and Leone³⁹ advocated use of a targeted Spo₂ protocol in the DR. Three randomized trials showed that it was possible to titrate the fraction of inspired oxygen in the DR by using Spo₂ target ranges.^27,37,40

In response to the debate on room air versus 100% oxygen, Kattwinkel² suggested that “we should be aiming to restore normoxia quickly and to achieve normal levels of blood oxygen throughout and beyond the resuscitation process. More aggressive use of the pulse oximeter in the delivery setting may facilitate achieving this goal.” The best definition of “normoxia” is that which leads to the best short- and long-term outcomes after resuscitation. There is currently insufficient evidence to specify the optimal concentration of oxygen to be used at the initiation of resuscitation, and studies to compare different ranges of normoxia will take many years. Until then, our percentile charts provide our best estimates of the appropriate Spo₂ targets during resuscitation. Once adequate ventilation has been established, these charts may help guide clinicians in titrating oxygen concentrations to specific targets at different times after birth.