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Background: Oxygen saturation (Spo2) monitors are commonly used to determine the need for supplemental oxygen. We aimed to describe the range of arterial oxygen tensions (Pao2) observed in preterm infants at saturation levels targeted in current trials. Methods: In a cohort of 98 consecutive infants born at

Introduction: Hyperoxia and variable oxygenation are associated with morbidity in preterm infants. The optimal range of oxygen tensions is not known. This study aimed to determine whether care based on transcutaneous oxygen tension (TcPo2) or saturation (Spo2) monitoring is associated with less time spent with high oxygen tension and less variability of oxygenation. Methods: Spo2 and TcPo2 were measured simultaneously during two 3-h study periods allocated in random order. During one period supplemental oxygen was adjusted according to TcPo2 (target range 6.0–9.0 kPa) and during the other according to Spo2 (target range 86–94%). During each period, readings from the second monitor were not displayed. Both TcPo2 and Spo2 were downloaded every second. For each period the mean level and the variability (standard deviation) of Spo2 and TcPo2 and the percentage of time spent above and below target range were calculated and compared. Results: 19 infants, 13 ventilated and 6 on continuous positive airway pressure, were studied at mean corrected gestational age of 27.2 weeks and mean postnatal age of 6.8 days. Their mean fraction of inspired oxygen at the start of the study was 0.34. Care based on Spo2 monitoring was associated with more time spent with high oxygen tension (median increase 2.62%, p = 0.01), more time with low oxygen tension (median increase 17.41%, p = 0.01), more variability in oxygen tension (median increase 0.28 kPa, p = 0.02) and more variability in oxygen saturation (median increase 0.82%, p = 0.01) than care based on TcPo2 monitoring. Conclusion: Within the target ranges studied Spo2 monitoring was associated with significantly more variable oxygenation than TcPo2 monitoring.