Oxygen targeting in preterm infants: a physiological interpretation

Randomized controlled trials evaluating low-target oxygen saturation (SpO(2):85% to 89%) vs high-target SpO(2) (91% to 95%) have shown variable results regarding mortality and morbidity in extremely preterm infants. Because of the variation inherent to the accuracy of pulse oximeters, the unspecified location of probe placement, the intrinsic relationship between SpO2 and arterial oxygen saturation (SaO(2)) and between SaO(2) and partial pressure of oxygen (PaO2) (differences in oxygen dissociation curves for fetal and adult hemoglobin), the two comparison groups could have been more similar than dissimilar. The SpO(2) values were in the target range for a shorter period of time than intended due to practical and methodological constraints. So the studies did not truly compare 'target SpO(2) ranges'. In spite of this overlap, some of the studies did find signficant differences in mortality prior to discharge, necrotizing enterocolitis and severe retinopathy of prematurity. These differences could potentially be secondary to time spent beyond the target range (SpO(2) <85 or >95%) and could be avoided with an intermediate but wider target SpO(2) range (87% to 93%). In conclusion, significant uncertainty persists about the desired target range of SpO(2) in extremely preterm infants. Further studies should focus on studying newer methods of assessing oxygenation and strategies to limit hypoxemia (<85% SpO(2)) and hyperoxemia (>95% SpO(2)).