Oximetry neither to prescribe long-term oxygen therapy nor to screen for severe hypoxaemia

BACKGROUND AND OBJECTIVE: Transcutaneous pulse oximetry saturation (S(pO(2))) is widely used to diagnose severe hypoxaemia and to prescribe long-term oxygen therapy (LTOT) in COPD. This practice is not based on evidence. The primary objective of this study was to determine the accuracy (false positive and false negative rates) of oximetry for prescribing LTOT or for screening for severe hypoxaemia in patients with COPD. METHODS: In a cross-sectional study, we correlated arterial oxygen saturation (S(aO(2))) and S(pO(2)) in patients with COPD and moderate hypoxaemia (n=240) and calculated the false positive and false negative rates of S(aO(2)) at the threshold of ≤88% to identify severe hypoxaemia (arterial oxygen tension (P(aO(2))) ≤55 mmHg or P(aO(2)) <60 mmHg) in 452 patients with COPD with moderate or severe hypoxaemia. RESULTS: The correlation between S(aO(2)) and S(pO(2)) was only moderate (intra-class coefficient of correlation: 0.43; 95% confidence interval: 0.32–0.53). LTOT would be denied in 40% of truly hypoxaemic patients on the basis of a S(aO(2)) >88% (i.e., false negative result). Conversely, LTOT would be prescribed on the basis of a S(aO(2)) ≤88% in 2% of patients who would not qualify for LTOT (i.e., false positive result). Using a screening threshold of ≤92%, 5% of severely hypoxaemic patients would not be referred for further evaluation. CONCLUSIONS: Several patients who qualify for LTOT would be denied treatment using a prescription threshold of saturation ≤88% or a screening threshold of ≤92%. Prescription of LTOT should be based on P(aO(2)) measurement.