Expected Variations in Nocturnal Oxygen Saturation in Infants: Comparing Needs at Sea Level to High Altitude

What is a normal overnight oxygen saturation for a child? This question is asked frequently by parents who have a child that may be requiring oxygen after evaluation. As healthcare providers working at various altitudes and caring for children, knowing the change in baseline oxygen saturations when at different altitudes is key to educating patients.  There are physiologic changes that result in transient changes in respiratory rate and volume while sleeping which will be discussed before exploring nocturnal oxygen needs at sea level versus needs at high altitude in healthy children. 

To begin, I will define a few terms that may not be familiar, but may be used when discussing oxygen needs. Oxygen saturation is defined as the amount of oxygen bound to hemoglobin in the blood, expressed as a percentage of maximal binding capacity.1 The simplest and most non-invasive way to obtain this information is through a pulse oximeter, which is placed on the patient’s finger, toe, or ear when vital signs are being taken. Oxygen saturation is known as the “5th vital sign” and tells medical providers whether or not a patient is delivering enough oxygen to their body. Hypoxemia is defined as insufficient oxygenation of the blood.2 There are multiple causes of hypoxemia, however we categorize hypoxemia as an oxygen saturation of less than 90 percent on a pulse oximeter. Finally, we use the term desaturation to describe a patient whose oxygen saturation continues to go below expected values.

In healthy, full-term infants, sleeping approximately 16 to 18 out of 24 hours is expected. A majority of their sleep cycle is REM and occurs when they fall asleep, with shorter duration of NREM sleep. As the child’s nervous system matures, there will be predictable changes in their sleep cycle, which will be more similar to a child or an adolescent. In children and adolescents, NREM is entered when they initially fall asleep, and accounts for approximately 75 percent of total sleep time, with alterations every 90 to 100 minutes of REM and NREM. In addition, there is a progressive increase in REM in the final third of the night.3 Understanding these cycles, what occurs during these cycles, and how they change over time are important in understanding the physiological changes (Table 1) that occur while you are sleeping.

  The physiological changes that we are focused on are decreased respiratory rate and decreased respiratory volume, which are seen in NREM and in the phasic stage of REM. In infants, periodic breathing is also an observed pattern of breathing that is expected after the first 48 hours of life until about 6 months of age. Periodic breathing is recurrent central apnea interrupted by breathing efforts. This topic will further be discussed in the high-altitude study, as these episodes are more common at high altitude.4

Table 1: Normal physiologic changes during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.5

In a study conducted at sea level in Brisbane, Queensland, Australia, 34 healthy term infants were studied at 2 weeks, 3, 6, 12, and 24 months in a prospective longitudinal cohort study. The study mentioned that there was limited data on reference ranges for normal nocturnal oxygen in infants, but that they aimed to develop a cumulative frequency (CF) reference-curve. This curve may be used as a tool to compare a child’s nocturnal oxygen saturation to see if the infant falls within the range for infants that are similar in age (Figure 1). Overall, the median nocturnal saturation was between 98 and 99 percent, for infants living at sea level.6 

In an additional study, conducted at high altitude in Bogotá, Colombia, 122 healthy full-term infants were studied in 4 various groups. These groups were coupled differently and were only monitored until 18 months of age. The groups were <45 days, 3 to 4 months, 6 to 7 months, and 10 to 18 months. In addition to these groups, 50 infants completed three overnight PSG studies and were analyzed as a longitudinal sub-cohort.

In this study, their overall data was presented differently and they also looked at SpO2 during wakefulness and respiratory events, which are more likely to occur at higher altitudes. An interesting finding, that was not present in the study at sea level in patients of similar size, age, and weight, was the increase in total, central, and obstructive apneas. In addition, there were also very high frequency oxygen desaturation events that again are not seen when living at lower altitudes. These events were reported as normal in infants living at high altitude. Overall, the median SpO2 was between 92 and 94 percent at high altitude.7 

To conclude, the median oxygen saturations at sea level were between 98 and 99 percent and between 92 and 94 percent at high-altitude. This said periodic breathing, which is normal until six months of age at any altitude, causes transient desaturations and are more common at high altitude. Apneic events are more commonly seen in infants at altitude, but are considered normal.  These studies have offered reference ranges and tools to better aid clinical judgement when caring for a patient that may require oxygen.

Felicia S.

References:

1. Oxygen saturation. Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. (2003). Retrieved March 23, 2019, from https://medical-dictionary.thefreedictionary.com/oxygen+saturation.

2. Hypoxemia. The American Heritage® Medical Dictionary. (2007). Retrieved March 23, 2019, from https://medical-dictionary.thefreedictionary.com/hypoxemia.

3. Wise, M., and Glaze, D. (2018). Sleep physiology in children. UpToDate. Retrieved March 23, 2019, from https://www-uptodate-com.ezproxy.stfrancis.edu/contents/sleep-physiology-in-children?search=sleep%20physiology%20in%20children&source=search_result&selectedTitle=1~134&usage_type=default&display_rank=1#H4. 

4. MacLean, J.E., Fitzgerald, D., & Waters, K. (2015). Developmental changes in sleep and breathing across infancy and childhood. Pediatric Respiratory Reviews, 16(4), 276-284.

5. Hanyang Medical Reviews. 2013 Nov;33(4):190-196. https://doi.org/10.7599/hmr.2013.33.4.190.

6. Terrill, P., Dakin, C., Hughes, I., Yuill, M., & Parsley, C. (2015). Nocturnal oxygen saturation profiles of healthy term infants. Archives of Disease in Childhood, 100(1), 18-23. 

7. Duenas-Meza, E., Bazurto-Zapata, M., Gozal, D., Gonzalez-Garcia, M., Duran-Cantolla, J., Torres-Duque, C. (2015) Overnight Polysomnographic Characteristics and Oxygen Saturation of Healthy Infants, 1 to 18 Months of Age, Born and Residing at High Altitude (2,640 Meters). Chest, 148(1), 120-127.