Abstract
Background. Preterm infants are at a higher risk for adverse outcomes, including cardiovascular, respiratory, growth, and developmental deficits. Apnoea of prematurity, or the intermittent cessation of breathing in a preterm infant, is a common sequela of preterm birth. Although usually treated with caffeine during the neonatal period, there exists what has been proposed as a baseline level of apnoea of prematurity (AOP) that may be attributed to the immaturity of the preterm infants' respiratory responses to hypoxia and hypercarbia. This may persist after cessation of caffeine before discharge. Intermittent hypoxia (IH), or brief drops in blood oxygen levels, is a sequela of AOP and has been observed in preterm infants who appear stable. Recent advancements in oximetry technology have allowed for the detection of shorter IH episodes, while software has facilitated the removal of artefactual data. Previous studies have shown the presence of IH in preterm infants in the first few months of life. The use of long-duration oximetry monitoring of well-appearing preterm and term infants pre-discharge remains inconsistent across Australasian neonatal centres. To date, normal ranges for values of IH have not been described.
Aims and Methods. This international multi-centre longitudinal observational study aimed to evaluate the prevalence and impact of IH on preterm and term infants up to 12 months corrected gestational age (CGA) in New Zealand with a separate discharge study in China. Long-duration oximetry monitoring was used to quantify IH and assess cardiorespiratory stability. Independent oximetry measures were identified for ease of analysis, including the Desaturation Index 4% (DSI4%), the number of episodes in which oxygen saturation levels dropped by ≥4% from baseline. A cut-off of DSI4% >55 events/hour was used to identify infants who may be more likely to have respiratory instability. Anthropometry was recorded throughout the study, with development assessed at 12 months CGA in the New Zealand cohort.
Findings. IH was present in preterm infants at discharge with a DSI4% of 52.6 (30.1-66.3) events/hour, with a significant decrease by 42 weeks postmenstrual age (PMA) with DSI4% of 18.8 (9.9-25.2) events/hour. IH was present in term infants at 42 weeks PMA with DSI4% of 31.4 (25.6-38.8) events/hour with a marked decrease by 4 months CGA. Term infants in the New Zealand cohort had a significantly greater degree of IH at 42 weeks PMA as compared to preterm infants, though this difference became insignificant from 4 months CGA onwards. IH at discharge and up to 42 weeks PMA was associated with an increased risk of growth and developmental deficits in later infancy. No significant difference in IH was found between the New Zealand and Chinese cohorts at discharge or 42 weeks PMA.
Conclusions. IH was present in well-appearing preterm and term infants at discharge, with the potential for sequelae later in infancy. Long-duration oximetry monitoring providing data such as the DSI4%, among other measures, can provide insight into the respiratory stability of an infant. Long-duration oximetry can be considered as a screening tool in high-risk infants requiring closer monitoring or intervention to mitigate adverse outcomes in the post-neonatal period. This research documents normal ranges for DSI4% in apparently healthy preterm and term infants up to 12 months CGA.