Determining a target SpO2 to maintain PaO2 within a physiological range

Objective In the context of an ongoing debate on the potential risks of hypoxemia and hyperoxemia, it seems prudent to maintain the partial arterial oxygen pressure (PaO 2 ) in a physiological range during administration of supplemental oxygen. The PaO 2 and peripheral oxygen saturation (SpO 2 ) are closely related and both are used to monitor oxygenation status. However, SpO 2 values cannot be used as an exact substitute for PaO 2 . The aim of this study in acutely ill and stable patients was to determine at which SpO 2 level PaO 2 is more or less certain to be in the physiological range. Methods This is an observational study prospectively collecting data pairs of PaO 2 and SpO 2 values in patients admitted to the emergency room or intensive care unit (Prospective Inpatient Acutely ill cohort; PIA cohort). A second cohort of retrospective data of patients who underwent pulmonary function testing was also included (Retrospective Outpatient Pulmonary cohort; ROP cohort). Arterial hypoxemia was defined as PaO 2 < 60 mmHg and hyperoxemia as PaO 2 > 125 mmHg. The SpO 2 cut-off values with the lowest risk of hypoxemia and hyperoxemia were determined as the 95th percentile of the observed SpO 2 values corresponding with the observed hypoxemic and hyperoxemic PaO 2 values. Results 220 data pairs were collected in the PIA cohort. 95% of hypoxemic PaO 2 measurements occurred in patients with an SpO 2 below 94%, and 95% of hyperoxemic PaO 2 measurements occurred in patients with an SpO 2 above 96%. Additionally in the 1379 data pairs of the ROP cohort, 95% of hypoxemic PaO 2 measurements occurred in patients with an SpO 2 below 93%. Conclusion The SpO 2 level marking an increased risk of arterial hypoxemia is not substantially different in acutely ill versus stable patients. In acutely ill patients receiving supplemental oxygen an SpO 2 target of 95% maximizes the likelihood of maintaining PaO 2 in the physiological range.