SpO2 values in acute medical admissions breathing air—Implications for the British Thoracic Society guideline for emergency oxygen use in adult patients?

SpO2 is routinely used to assess the well-being of patients, but it is difficult to find an evidence-based description of its normal range. The British Thoracic Society (BTS) has published guidance for oxygen administration and recommends a target SpO2 of 94–98% for most adult patients. These recommendations rely on consensus opinion and small studies using arterial blood gas measurements of saturation (SaO2). Using large datasets of routinely collected vital signs from four hospitals, we analysed the SpO2 range of 37,593 acute general medical inpatients (males: 47%) observed to be breathing room air. Age at admission ranged from 16 to 105 years with a mean (SD) of 64 (21) years. 19,642 admissions (52%) were aged <70 years. SpO2 ranged from 70% to 100% with a median (IQR) of 97% (95–98%). SpO2 values for males and females were similar. In-hospital mortality for the study patients was 5.27% (range 4.80–6.27%). Mortality (95% CI) for patients with initial SpO2 values of 97%, 96% and 95% was 3.65% (3.22–4.13); 4.47% (3.99–5.00); and 5.67% (5.03–6.38), respectively. Additional analyses of SpO2 values for 37,299 medical admissions aged ≥18 years provided results that were distinctly different to those upon which the current BTS guidelines based their definition of normality. Our findings suggest that the BTS should consider changing its target saturation for actively treated patients not at risk of hypercapnic respiratory failure to 96–98%.