Sample entropy of oxygen saturation in preterm infants

Bronchopulmonary dysplasia (BPD) is the most common respiratory complication after preterm birth. Early preventive measures are important to reduce further damage on lung tissue. Thus, early discrimination between infants with and without BPD is of high importance. A low sample entropy (SampEn) of time series of the oxyhemoglobin saturation (SpO(2)-SampEn for short) is associated with an increased risk of hypoxemic events in neonates. We hypothesized that preterm infants have a lower SpO(2)-SampEn compared to term infants. Moreover, that infants with BPD have a lower SpO(2)-SampEn compared to those without BPD. Preterm infants < 32 w gestation and healthy term infants were eligible for study. We recorded SpO(2) over 90 min through the clinical monitoring system with a sampling frequency of 0.98 Hz and calculated the SpO(2)-SampEn at 32 w postmenstrual age (PMA), 36 w PMA, and at discharge. We included 95 term and 180 preterm infants, of whom 44 (24.4%) developed BPD. SpO(2)-SampEn was lower in preterm infants compared to term infants. SpO(2)-SampEn was lower in infants with BPD compared to infants without BPD at 32 w PMA. However, gestational age was the only predictor of SampEn at 32 w PMA. This difference between infants with and without BPD was no longer present at 36 w PMA and discharge. SpO(2)-SampEn can be utilized to discriminate between preterm and term infants and between preterm infants with and without BPD. However, confounding factors such as caffeine therapy, gestational age and the natural boundary of 100% of SpO(2) values have to be considered.