Objective Describe the likelihood of hypoxemia and hyperoxemia across ranges of oxygen saturation (SpO₂), during mechanical ventilation with supplemental oxygenation.

Design Retrospective observational study.

Setting University affiliated tertiary care neonatal intensive care unit.

Patients Two groups of neonates based on postmenstrual age (PMA): <32 weeks (n=104) and >36 weeks (n=709).

Main measures Hypoxemia was defined as a PaO₂ <40 mm Hg, hyperoxemia as a PaO₂ of >99 mm Hg and normoxemia as a PaO₂ of 50–80 mm Hg. Twenty-five per cent was defined as marked likelihood of hypoxemia or hyperoxemia.

Results From these infants, 18 034 SpO₂–PaO₂ pairs were evaluated of which 10% were preterm. The PMA (median and IQR) of the two groups were: 28 weeks (27–30) and 40 weeks (38–41). With SpO₂ levels between 90% and 95%, the likelihoods of hypoxemia and hyperoxemia were low and balanced. With increasing levels of SpO₂, the likelihood of hyperoxemia increased. It became marked in the preterm group when SpO₂ was 99%–100% (95% CI 29% to 41%) and in the term group with SpO₂ levels of 96%–98% (95% CI 29% to 32%). The likelihood of hypoxemia increased as SpO₂ decreased. It became marked in both with SpO₂ levels of 80%–85% (95% CI 20% to 31%, 24% to 28%, respectively).

Conclusions The likelihood of a PaO₂ <40 mm Hg is marked with SpO₂ below 86%. The likelihood of a PaO₂ >99 mm Hg is marked in term infants with SpO₂ above 95% and above 98% in preterm infants. SpO₂ levels between 90% and 95% are appropriate targets for term and preterm infants.