113 6 The effect of AOC on clinical outcomes in preterm infants: a pre- and post- study Discussion In this retrospective study, we compared two large cohorts of preterm infants admitted to the NICU before and after implementation of AOC. Implementation led to no change in mortality and morbidities in preterm infants admitted to the NICU, despite a shift towards more non-invasive ventilation. The rates of mortality and morbidities were not very different from previous studies reporting short term outcome in infants < 30 weeks of gestation. 1, 31 Although we recently demonstrated that infants spent more time within TR after implementation of AOC, this does not seem to have had a clinically relevant impact in a large cohort. This is the first study reporting on the effect of AOC on clinical outcome in preterm infants when this is implemented as standard of care. Several observational studies and clinical trials have demonstrated a beneficial effect of AOC on time spent within TR.12-19 Although all authors speculated that this could affect clinical and neurodevelopmental outcome, these studies were not designed to demonstrate a difference in clinical outcome. To the best of our knowledge there are no completed studies directly relating the achieved time within TR to clinical outcome. However, post-hoc analysis of the SUPPORT trial7 demonstrated an increase in mortality for infants with a lower median SpO2. This could suggest that when 91%-95% is considered the appropriate TR, more time under this range could lead to a lower median SpO2 and associated increase in mortality. Post-hoc analysis from the BOOST-II UK trial32 also demonstrated that a lower achieved oxygen distribution was associated with an increase in NEC and mortality. Using AOC in clinical practice could lead to a leftward shift of the SpO2 distribution. Bedside staff would seem to prefer to target higher SpO2 values within a prescribed range,33 whereas AOC devices for the most part target the middle SpO2 value of the TR, potentially leading to a lower median SpO2. A further consideration raised in regard to AOC implementation is that clinical deterioration may be masked, with possible adverse effects.34 However none of the AOC trials have reported this and our current findings showed no sign of this possible detrimental effect, with rates of mortality and morbidity similar between cohorts and in relation to previous studies.1, 31 Indeed, it can be argued that continual assessment and display of the basal oxygen requirement as well as the number and magnitude of interventions by the AOC device could be used as an additional objective indicator of clinical deterioration. A large randomised controlled trial, the FiO2-C study 35, comparing AOC using any of the commercially available algorithms with manual titration, is currently being undertaken and will provide more data on the effect of AOC on clinical outcome.