Discrepancies between arterial oxygen saturation and functional oxygen saturation measured with pulse oximetry in very preterm infants

Background: Discrepancies between pulse oximetry saturation (SpO(2)) and arterial saturation (SaO(2)) at low blood oxygenation values have been previously reported with significant variations among instruments and studies. Whether pulse oximeters that attenuate motion artifact are less prone to such discrepancies is not well known.

Objective: To prospectively assess the agreement of the Masimo V4 pulse oximeter within the critical 85-95% SpO(2) target range.

Patients and methods: For all consecutive babies with gestational age <33 weeks, postnatal age <7 days, and an umbilical arterial line, SpO(2) was measured continuously and SaO(2) analyzed on an as-needed basis. Bland-Altman techniques provided estimates of the difference (D = SaO(2) - SpO(2)), standard deviation (SD), and 95% limits of agreement (D ± 2*SD).

Results: There were 1,032 measurements (114 babies) with SpO(2) between 85 and 95%. The 95% limits of agreement were -2.0 ± 5.8, -2.4 ± 9.2, and -1.9 ± 5.3 in the SpO(2) categories 85-95, 85-89, and 91-95%, respectively. For the SpO(2) categories 85-89% and 91-95%, only 52% (53/101) and 59% (523/886) of SpO(2) values, respectively, corresponded to the analogous SaO(2) categories. In the 85-89% SpO(2) category, SaO(2) was lower than 85% in 39 of the 101 (39%) measurements.

Conclusion: SaO(2) was lower on average than SpO(2) with an increased bias at lower saturation. The -2.4 ± 9.2 95% limits of agreement for SaO(2) - SpO(2) in the 85-89% SpO(2) category suggest that SpO(2) and SaO(2) are not interchangeable and intermittent SaO(2) assessments are warranted when the targeted SpO(2) is within this range.