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Earlier Apgar Score Increase in Severely Depressed Term Infants Cared for in Swedish Level III Units With 40% Oxygen Versus 100% Oxygen Resuscitation Strategies: A Population-Based Register Study

Lena Hellström-Westas, MD, PhD^a, Kristina Forsblad, MD^b, Gunnar Sjörs, MD, PhD^c, Ola Didrik Saugstad, MD, PhD^d, Lars J. Björklund, MD, PhD^a, Karel Marál, MD, PhD^e and Karin Källén, PhD^f

^a Departments of Pediatrics
^e Obstetrics and Gynecology, Lund University Hospital, Lund, Sweden
^b Department of Pediatrics, Helsingborg Hospital, Helsingborg, Sweden
^c Department of Pediatrics, Uppsala University Hospital, Uppsala, Sweden
^d Department of Pediatric Research, Faculty Division of Medicine, Rikshospitalet Medical Center, University of Oslo, Oslo, Norway
^f Perinatal Epidemiology Research Center, Tornblad Institute, Lund University, Lund, Sweden

	ABSTRACT

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OBJECTIVES. The aim of this study was to evaluate whether a resuscitation strategy based on administration of 40% oxygen influences mortality rates and rates of improvement in 5-minute Apgar scores, compared with a strategy based on 100% oxygen administration.

METHODS. A population-based study evaluated data from 4 Swedish perinatal level III centers during the period of 1998 to 2003. During this period, the centers used either of 2 resuscitation strategies (initial oxygen administration of 40% or 100%). Live-born, singleton, term infants with 1-minute Apgar scores of <4, with a birth weight appropriate for gestational age, and without major malformations were included in the study (n = 1223).

RESULTS. Infants born in hospitals using a 40% oxygen strategy had a more rapid Apgar score increase than did infants born in hospitals using a 100% oxygen strategy; however, no difference remained at 10 minutes. The mean Apgar score increased from 2.01 at 1 minute to 6.74 at 5 minutes in the 2 hospitals initiating resuscitation with 40% oxygen, compared with 2.01 to 6.38 in the 2 hospitals using 100% oxygen, with a mean difference in Apgar score increases of 0.36. At 5 minutes, 44.3% of infants born in the hospitals using 100% oxygen had an Apgar score of <7, compared with 34.0% of infants at the hospitals using 40% oxygen. At 10 minutes, the mean Apgar scores were 8.16 at the hospitals using 40% oxygen and 8.07 at the hospitals using 100% oxygen. There were no significant differences in rates of neonatal death, hypoxic ischemic encephalopathy, or seizures in relation to the 2 oxygen strategies.

CONCLUSION. Severely depressed term infants born in hospitals initiating resuscitation with 40% oxygen had earlier Apgar score recovery than did infants born in hospitals using a 100% oxygen strategy.

Key Words: Apgar score • term • newborn • oxygen • resuscitation

Abbreviations: MBR—Medical Birth Register • CI—confidence interval • OR—odds ratio

Benefits and possible risks of resuscitation of newborn infants with room air or oxygen are currently under debate. In 2000, international guidelines recommended that 100% oxygen should be used if assisted ventilation is required.¹ The 2005 guidelines still recommend the use of supplemental oxygen in this situation but do not advocate a specific oxygen concentration.^2,3 Several studies showed previously that room air may be as efficient as 100% oxygen for resuscitation of newborn infants and may be associated with quicker recovery, lower mortality rates, and lower risk for oxidative stress.^4–11

Swedish neonatologists have used a joint neonatal resuscitation program since 1972. Initial recommendations, created by leading neonatologists and obstetricians, later formed the basis for guidelines issued by the Swedish Society of Perinatal Medicine. The Swedish guidelines differ slightly from the 2000 international guidelines,¹ with more emphasis on initial evaluation of primary versus secondary apnea¹² and use of a higher dose of epinephrine (0.05 mg/kg). If an infant does not start breathing spontaneously after birth, then the attending midwife or doctor should evaluate the heart rate immediately. If the rate is >100 beats per minute, then the infant is experiencing primary apnea, which indicates that assisted ventilation can be postponed for 15 to 30 seconds while the effects of positioning, clearing of the airway, and sensory stimulation are awaited. A heart rate of <100 beats per minute, however, usually indicates secondary apnea, and assisted ventilation should be started immediately, initially by face mask. If the heart rate does not increase immediately, then the inflation pressure and inspiration time should be increased. If the heart rate is still <100 beats per minute at 2 minutes of age, then the infant should be intubated; if bradycardia persists, then epinephrine should be administered. In a case of apparent stillbirth (ie, if no heart activity is detected at birth), then the infant should be intubated immediately, ventilated, and given chest compressions. A majority of Swedish hospitals have followed these guidelines, except for 1 academic referral center with a level III NICU and a few hospitals with level II NICUs, which have chosen to follow the international guidelines.¹

In 1997, the Swedish guidelines were revised and the previous recommendation to initiate resuscitation with 100% oxygen was changed to 40% oxygen. This change, from 100% to 40% oxygen, was a compromise based on experimental data and clinical studies indicating room air to be as efficient as 100% oxygen for neonatal resuscitation and on possible risks of oxidative stress.^13–19 Although most Swedish hospitals changed their routines in 1997 to initiate resuscitation with 40% oxygen, a few hospitals, including 2 of the 7 level III perinatal centers in Sweden, continued to use 100% oxygen.

A recent meta-analysis showed that resuscitation with room air is associated with better recovery of 5-minute Apgar scores and lower mortality rates.¹⁰ However, there are few studies investigating the effects of oxygen concentrations between room air and 100% during resuscitation. The aim of the present study was to investigate whether resuscitation strategies using 40% and 100% oxygen are associated with differences in Apgar score recovery.

	METHODS

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Data from 4 Swedish academic perinatal centers were evaluated. The infants were born during a 6-year period, from 1998 to 2003. The 4 perinatal units are referral centers for high-risk pregnancies, with level III NICUs. Two centers used 100% oxygen for resuscitation (centers A1 and A2), and 2 comparable units were chosen because they used a strategy based on initial resuscitation with 40% oxygen (centers B1 and B2) (Table 1). Centers A1 and B1 are located in university towns with 100000 to 200000 inhabitants and 3000 to 4000 deliveries per year. Centers A2 and B2 are referral centers in metropolitan areas with >500000 inhabitants, and both hospitals have >4000 deliveries per year.

View this table: [in this window] [in a new window]   TABLE 1 Characteristics of the 4 Included Swedish Level III Perinatal Centers, Including the Total Numbers of Live-Born Infants (Born at 37 Weeks of Gestation With Birth Weight Appropriate for Gestational Age) and the Proportions of Infants With 1-Minute Apgar Scores of Less Than 4

Infants with malformation diagnoses were excluded, except for preauricular skin tags, hip dysplasia, single umbilical artery, and nevus, because these diagnoses were not considered to increase risks during delivery and response to resuscitation. Neonatal death and the presence of the diagnoses of hypoxic ischemic encephalopathy (International Classification of Diseases, 10th Revision, code P910) and neonatal seizures (International Classification of Diseases, 10th Revision, code P909) were evaluated in relation to the mode of resuscitation (100% or 40% oxygen).

Apgar score changes were analyzed by using both nonparametric and parametric tests; both medians and means are presented. It may be argued that the mean is not an appropriate summary statistic for Apgar scores, because this score is not a continuous quantitative variable with a symmetric distribution. However, because some studies reported means, including one of the meta-analyses,¹⁰ we chose to do the same. Differences in the mean Apgar scores at 1, 5, and 10 minutes and differences in the mean Apgar score increases between 1 and 5 minutes were evaluated by using analysis of covariance, with adjustment for year of birth, maternal age, parity, smoking, metropolitan/university town hospital, and (if appropriate) 1-minute Apgar score.

The difference between the strategies regarding the Apgar score increases from 1 to 10 minutes was evaluated by using mixed-effect models for repeated-measurement data, and the differences in mortality and morbidity rates were analyzed by using multivariate logistic regression models (Gauss; Aptec Systems, Maple Valley, WA). In the multivariate logistic regression analyses, forward selection was used to identify the most important confounders, so that the number of independent variables never exceeded one tenth of the number of cases. The putative confounders were chosen from the sample as mentioned earlier, that is, year of birth, maternal age, parity, smoking, actual 1-minute Apgar score, and metropolitan/university town hospital. The study was approved by Lund University Research Ethics Committee and the Epidemiology Unit at the National Board of Health and Welfare.

	RESULTS

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During the 6-year period, 93486 singleton, term, live-born infants with birth weight appropriate for gestational age and without major malformations were born at the 4 centers. Of those infants, 1223 had 1-minute Apgar scores of <4 and were included in the analysis. The 2 larger metropolitan hospitals (centers A2 and B2) had higher rates of low 1-minute Apgar scores (scores of <4) than did the hospitals in the 2 smaller towns (Table 1).

The proportions of infants who were born through cesarean section did not differ between the 2 strategies (38.1% and 38.7% for the 100% and 40% oxygen groups, respectively). Table 2 shows descriptive data for Apgar scores at 1, 5, and 10 minutes. For 1-minute and 10-minute Apgar scores, neither the nonparametric test nor the analysis of covariance indicated any difference between the oxygen strategies. At 5 minutes, the mean Apgar score among infants born in units with a 40% oxygen strategy was significantly higher than the corresponding mean among infants born in units with a 100% oxygen strategy. An analysis of covariance was performed to test for a true difference between the oxygen strategies with respect to the mean Apgar score increase between 1 and 5 minutes (Table 3). The adjusted estimates are shown despite the fact that adjustment for various confounders influenced the results only marginally.

View larger version (47K): [in this window] [in a new window]   FIGURE 1 Apgar scores at 1, 5, and 10 minutes for each infant (thin lines) and estimates from mixed-effects models (bold lines). A, 40% oxygen; B, 100% oxygen. Detailed results from the mixed-effect models are shown in the Appendix.

	DISCUSSION

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In the current population-based study, severely depressed infants who were born in centers using a 40% oxygen resuscitation strategy had a larger increase in Apgar scores from 1 to 5 minutes, compared with infants born in centers using 100% oxygen, but no significant difference in mean Apgar scores remained at 10 minutes. These findings agree with previous studies and a recent meta-analysis comparing resuscitation with room air versus 100% oxygen.^5,10 However, no clinical studies evaluated previously 40% oxygen versus 100% oxygen resuscitation of term infants. For this purpose, the Swedish MBR offers a unique possibility for investigating population effects on Apgar score development with the different oxygen resuscitation strategies, because at least 98% to 99% of all deliveries are recorded, including data on Apgar scores.

The higher rate of low 1-minute Apgar scores at the 2 larger hospitals can probably be explained by the fact that the hospitals are in metropolitan areas with mixed populations with higher perinatal risks. This was also a reason for matching the 2 centers using a 100% oxygen strategy with comparable centers using a 40% oxygen strategy. Other data for comparison of perinatal status between infants born at the 4 centers (eg, umbilical cord pH, subscores for the Apgar scores, or socioeconomic status) were not available. However, previous studies showed poor correlation between total Apgar scores and umbilical cord pH values, although 1-minute subscores for muscle tone, reflex irritability, and respiration were associated with arterial and venous cord blood pH values.^20,21

Low Apgar scores are more common among twins and among infants who are large for gestational age. Because low Apgar scores may be attributable to several factors for such infants, those infants were excluded from the present analysis.²¹ However, low Apgar scores are not always attributable to birth asphyxia; in a Swedish population-based study, it was estimated that congenital malformations, infections, and opioid-induced respiratory depression accounted for 20% of low Apgar scores (scores of <7) at 5 minutes.²² Therefore, we excluded infants with major malformations that could be associated with low Apgar scores (eg, diaphragmatic hernias or cardiac malformations), because such infants may respond differently to resuscitation than infants with perinatal compromise attributable to labor or infections. In the present study, 119 infants with the diagnoses of meconium aspiration, sepsis, or pneumonia were included. However, the results were the same when infants with these diagnoses were excluded from the analysis (data not shown). It was not possible to evaluate the effects of maternal opioid administration on the infants, because this variable was not recorded in the MBR.

The inclusion criterion in the current evaluation, a 1-minute Apgar score of <4, besides being accepted generally as a marker of severe postnatal depression, is not consistent with having full scores for heart rate and respiration at the same time.^22,23 A limitation of the present study is that, although it is highly likely that an infant with a 1-minute Apgar score of <4 would be resuscitated, it is not possible to evaluate from the MBR data whether all included infants were resuscitated actively and, if they were, how much oxygen was actually administered. Furthermore, because only the total Apgar score is noted in the MBR, it was not possible to evaluate the response in heart rate. Although pulse oximeters were available in all units during the study period, we do not know how many of the depressed infants were actually monitored, and saturation values were not reported to the registry. Therefore, our results cannot be compared with data from studies that evaluated responses in heart rate or oxygenation to resuscitation with 21% or 100% oxygen.²⁴

The participating hospitals used either a self-inflating bag system or a T-piece resuscitator (NeoPuff Infant Resuscitator, Fisher & Paykel Healthcare, Auckland, New Zealand). With the T-piece resuscitator, the concentration of administered oxygen is controlled accurately through the use of a gas blender; with the self-inflating bag system, however, the concentration of oxygen delivered to the infant depends on several factors, including ventilation rate, oxygen flow, and reservoir configuration. The consequence of this is that the actual oxygen delivery may differ from the intended oxygen concentration (100% or 40%). During the first years of the evaluation, center B1 did not use oxygen mixers but had the oxygen flow set at 2 L/min, which in bench experiments with the Laerdal self-expanding bag and mask was shown to deliver 40% oxygen (M. Lindroth, MD, PhD, oral communication, 1998 and 2005). Furthermore, the difference in resuscitation strategies, with 1 hospital (center A1) following the international guidelines and the other 3 following the Swedish national guidelines, might have resulted in slightly earlier initiation of ventilation at hospital A1.

The difference in mean Apgar scores of 0.4 between hospitals using 100% oxygen and those using 40% oxygen for resuscitation may seem trivial, especially because the difference disappeared at 10 minutes. However, our finding implies that infants born in hospitals using 100% oxygen had a 50% increased risk of having a 5-minute Apgar score of <7, compared with infants born in hospitals using 40% oxygen for resuscitation. Previous studies showed that term infants with 5-minute Apgar scores of 4 to 6 have considerably increased risk of death (relative risk: 45–53) and cerebral palsy (relative risk: 31), compared with infants with 5-minute Apgar scores of 7.^25–27 In the current context, evaluating the effects on Apgar scores of different resuscitation strategies, the optimal evaluation would also include long-term follow-up monitoring. However, there is no national register for cerebral palsy in Sweden, and the population-based MBR contains only perinatal variables.

	CONCLUSIONS

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The present data indicate that a resuscitation strategy based on administration of 40% oxygen is as efficient as one using 100% oxygen. The current data also support previous findings that resuscitation with oxygen concentrations of <100% is associated with earlier recovery, measured as a larger increase in Apgar scores between 1 and 5 minutes. The advantage of the present population-based study is the large number of evaluated infants (n = 1233), which is comparable to the total of 1302 infants in the 5 studies included in the Cochrane analysis.¹¹ Some of the previous studies comparing resuscitation with room air versus oxygen were criticized for being performed in developing countries, and the relevance of the findings was therefore questioned. The hospitals included in the present study are all academic referral centers with level III NICUs, in an industrialized country with a low perinatal mortality rate, and were chosen for the evaluation because they are comparable in size, organization, and competence in perinatal care. The relatively low 5-minute Apgar scores in the present evaluation (mean: 6.74 and 6.38 for infants born at hospitals with 40% and 100% oxygen resuscitation strategies, respectively) confirm that the included infants represent a high-risk population.

	ACKNOWLEDGMENTS

 
The present investigation was performed with financial support from the Swedish Medical Research Council (grants 0037 and 5980), the K. A. Wallenberg Foundation, and Lund University Hospital funds.

	FOOTNOTES

 
Accepted Jul 17, 2006.

Address correspondence to Lena Hellström-Westas, MD, PhD, Department of Pediatrics, University Hospital, SE-221 85 Lund, Sweden. E-mail:lena.hellstrom-westas{at}med.lu.se

The authors have indicated they have no financial relationships relevant to this article to disclose.

	REFERENCES

TOP ABSTRACT METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

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