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Determining the Relationship Between Thresholds of Cerebral Tissue Oxygenation and Adverse Outcomes in Preterm Infants

Presented at the Neonatal Society 2014 Autumn Meeting.

Ng I1, Costa CS2, Stevenson GN2, Austin T2

1 School of Clinical Medicine, University of Cambridge, UK
2 Neonatal Unit, The Rosie Hospital, Cambridge University Hospitals NHS Foundation Trust, UK

Background: Decreased cerebral perfusion is associated with brain injury in preterm infants. Management that targets cerebral oxygenation requires absolute thresholds of cerebral tissue oxygenation to be defined in the population group. This study investigates the relationship between deviations of cerebral tissue oxygenation beyond set thresholds and outcomes of mortality and intraventricular haemorrhage (IVH) in preterm infants in the immediate perinatal period.

Methods: 49 preterm infants born at median (range) gestational age of 26+6 weeks (23+4 – 31+0) were studied at a median (range) age of 11.7 (3.5-64) hours of life, following parental consent. Cerebral tissue oxygenation index (TOI) was measured using a NIRO200NX spectrophotometer1 and data were stored and analysed using ICM+ software2. We calculated burdens of TOI deviation beyond thresholds for hypoxia (<55%, <60%, <65%) and hyperoxia (>75%, >80%, >85%). Cumulative burdens of hypoxia were calculated in 6 hour windows in 26 infants who were continuously studied for a median duration of 43 hours. Outcomes were collected from clinical notes.

Results: Of the 49 infants studied, 8 died and 19 had IVH (grade 1 to 4). Burdens of hypoxia/hyperoxia were defined as the magnitude of deviation from thresholds multiplied by the proportion of study time spent outside the thresholds. Logistic regression analysis was used to compare different burden measures and outcomes. Significant log likelihood ratios for mortality were found with all burdens of hypoxia: TOI<55% (p=0.049), TOI<60% (p=0.011) and TOI<65% (p=0.013), as well as with total burden of hypoxia and hyperoxia with thresholds of TOI<60% + TOI>80% (p=0.018) and TOI<65% + TOI>75% (p=0.005). Student’s t-test or the Mann Whitney U test was used to compare mean cumulative burdens of hypoxia between infants who developed IVH and those who did not, after testing for normality with the Shapiro-Wilk test. There was significant difference found when hypoxia was defined as TOI<55% and TOI<60%, from 18 hours of life and beyond (p<0.05).

Conclusion: We have defined thresholds of TOI based on burden of hypoxia and adverse clinical outcomes. Cumulative burdens of hypoxia from 18 hours of life have shown significant association with IVH. Therefore, the burden of TOI deviation may be a useful clinical index, especially in the first few days of life in extremely preterm infants.

Corresponding author: ihxn2@cam.ac.uk

1. Hamamatsu Photonics, Hamamatsu, Japan; 2. Cambridge Enterprise, Cambridge, UK

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