Oxygen Therapy When is O2 Therapy Needed? Currently, the “standard” indication for supplemental oxygen therapy is a PaO2 < 60 mm Hg or a SaO2 of < 90% [Resp Care 47: 717, 2002], however arterial oxygen may be as low as 40 mm Hg in supine patients without producing hyperlactemia – this has been shown […]