Effect of a Lower Target Oxygen Saturation Range on the Risk of Hypoxaemia and Elevated NEWS2 Scores at a University Hospital: a Retrospective Study

Background: The optimal target oxygen saturation (SpO) range for hospital inpatients not at risk of hypercapnia is unknown. The objective of this study was to assess the impact on oxygen usage and National Early Warning Score 2 (NEWS2) of changing the standard SpO target range from 94-98% to 92-96%.

Methods: In a metropolitan UK hospital, a database of electronic bedside SpO measurements, oxygen prescriptions and NEWS2 records was reviewed. Logistic regression was used to compare the proportion of hypoxaemic SpO values (<90%) and NEWS2 records ≥5 in 2019, when the target SpO range was 94-98%; with 2022, when the target range was 92-96%.

Results: In 2019, 218 of 224 936 (0.10%) observations on room air and 162 of 11 328 (1.43%) on oxygen recorded an SpO <90%, and in 2022, 251 of 225 970 (0.11%) and 233 of 12 845 (1.81%), respectively (risk difference 0.04%, 95% CI 0.02% to 0.07%). NEWS2 ≥5 was observed in 3009 of 236 264 (1.27%) observations in 2019 and 4061 of 238 815 (1.70%) in 2022 (risk difference 0.43%, 0.36% to 0.50%; p<0.001). The proportion of patients using supplemental oxygen with hyperoxaemia (SpO 100%) was 5.4% in 2019 and 3.9% in 2022 (OR 0.71, 0.63 to 0.81; p<0.001).

Discussion: The proportion of observations with SpO <90% or NEWS2 ≥5 was greater with the 92-96% range; however, absolute differences were very small and of doubtful clinical relevance, in contrast to hyperoxaemia for which the proportion was markedly less in 2022. These findings support proposals that the British Thoracic Society oxygen guidelines could recommend a lower target SpO range.