Nocturnal oxygen saturation profiles of healthy term infants

Abstract

Objective: Pulse oximetry is used extensively in hospital and home settings to measure arterial oxygen saturation (SpO2). Interpretation of the trend and range of SpO2 values observed in infants is currently limited by a lack of reference ranges using current devices, and may be augmented by development of cumulative frequency (CF) reference-curves. This study aims to provide reference oxygen saturation values from a prospective longitudinal cohort of healthy infants.

Design: Prospective longitudinal cohort study.

Setting: Sleep-laboratory.

Patients: 34 healthy term infants were enrolled, and studied at 2 weeks, 3, 6, 12 and 24 months of age (N=30, 25, 27, 26, 20, respectively).

Interventions: Full overnight polysomnography, including 2 s averaging pulse oximetry (Masimo Radical).

Main outcome measurements: Summary SpO2 statistics (mean, median, 5th and 10th percentiles) and SpO2 CF plots were calculated for each recording. CF reference-curves were then generated for each study age. Analyses were repeated with sleep-state stratifications and inclusion of manual artefact removal.

Results: Median nocturnal SpO2 values ranged between 98% and 99% over the first 2 years of life and the CF reference-curves shift right by 1% between 2 weeks and 3 months. CF reference-curves did not change with manual artefact removal during sleep and did not vary between rapid eye movement (REM) and non-REM sleep. Manual artefact removal did significantly change summary statistics and CF reference-curves during wake.

Conclusions: SpO2 CF curves provide an intuitive visual tool for evaluating whether an individual's nocturnal SpO2 distribution falls within the range of healthy age-matched infants, thereby complementing summary statistics in the interpretation of extended oximetry recordings in infants.

Keywords: Measurement; Respiratory; Sleep; Technology.

Figure 1

Cumulative frequency (CF) reference-curves of SpO₂ profiles for a population of healthy term infants aged 2 weeks, 3, 6, 12 and 24 months. CF reference-curves are derived from the nocturnal SpO₂ recordings of 30, 25, 27, 26 and 20 infants at 2 weeks, 3, 6, 12 and 24 months of age, respectively, in a longitudinal follow-up study. Results are presented for the whole nocturnal recording, using CF plots calculated from oximetry data without manual artefact removal. The CF plot for an individual shows the percentage of a recording spent at, or below a particular SpO₂ value, while the CF reference-curve shows the range of percentage time spent below a particular SpO₂ value in the healthy term population. For example, it may be seen that in healthy infants at 2 weeks of age, between 0% and 60% of a recording may be spent with an SpO₂ of 95% or less. Notably, the CF reference-curves shift right by 1%–2% between 2 weeks and 3 months, where they remain stable up to 24 months.

Figure 2

SpO₂ cumulative frequency (CF) reference-curves for healthy infants aged 2 weeks–24 months, generated with and without manual artefact removal. CF reference-curves are shown for SpO₂ data from the whole nocturnal recording. At SpO₂ values greater than 95%, there is no discernible deviation between nomogram curves generated with and without manual artefact removal. At lower Spo₂ values, the maximum curve for data without manual artefact removal remains higher than the respective nomogram curve with manual artefact removal, indicating that artefact manually removed tends to be at lower SpO₂ values. Max (Man Artfct Remvl), population maximum reference-curve generated with manual artefact removal; Med (Man Artfct Remvl), population median reference-curve generated with manual artefact removal; Min (Man Artfct Remvl), population minimum reference-curve generated with manual artefact removal.

Figure 3

SpO₂ cumulative frequency (CF) reference-curves for healthy term infants and healthy preterm infants. CF reference-curves for healthy infants at 2 weeks, overlaid with the reference-curves presented by Harigopal et al for healthy preterm infants (median gestational age at birth of 33 weeks; median age at study of 2 weeks). The reference-curves for the preterm infant group are shifted to the left relative to the term infant group (median curve shifted approximately 3%–4% SpO₂). Physiological differences in the oxy-haemoglobin dissociation curve, use of different pulse-oximeter models and the extent of manual artefact removal may account for these differences.

Figure 4

Effect of supplemental oxygen on an infant with chronic neonatal lung disease at 3 months corrected age during an oxygen titration study. Cumulative frequency (CF) plots for an infant with chronic neonatal lung disease at 3 months gestational corrected age, plotted over the SpO₂ CF reference-curves for healthy infants at 3 months. It can be observed that when the infant is in room air, the CF plot is shifted to the left of the normative range indicating that SpO₂ values are lower than may be expected in healthy infants. However, when treated with 0.25 L/min of supplemental oxygen, the CF plot is within the healthy range indicating normal SpO₂ distribution.