Inverse association between blood pressure and pulse oximetry accuracy: an observational study in patients with suspected or confirmed COVID-19 infection.

BACKGROUND: Pulse oximeters are a standard non-invasive tool to measure blood oxygen levels, and are used in multiple healthcare settings. It is important to understand the factors affecting their accuracy to be able to use them optimally and safely. This analysis aimed to explore the association of the measurement error of pulse oximeters with systolic BP, diastolic BP and heart rate (HR) within ranges of values commonly observed in clinical practice. METHODS: The study design was a retrospective observational study of all patients admitted to a large teaching hospital with suspected or confirmed COVID-19 infection from February 2020 to December 2021. Data on systolic and diastolic BPs and HR levels were available from the same time period as the pulse oximetry measurements. RESULTS: Data were available for 3420 patients with 5927 observations of blood oxygen saturations as measured by pulse oximetry and ABG sampling within 30 min. The difference in oxygen saturation using the paired pulse oximetry and arterial oxygen saturation difference measurements was inversely associated with systolic BP, increasing by 0.02% with each mm Hg decrease in systolic BP (95% CI 0.00% to 0.03%) over a range of 80-180 mm Hg. Inverse associations were also observed between the error for oxygen saturation as measured by pulse oximetry and with both diastolic BP (+0.03%; 95% CI 0.00% to 0.05%) and HR (+0.04%; 95% CI 0.02% to 0.06% for each unit decrease in the HR). CONCLUSIONS: Care needs to be taken in interpreting pulse oximetry measurements in patients with lower systolic and diastolic BPs, and HRs, as oxygen saturation is overestimated as BP and HR decrease. Confirmation of the oxygen saturation with an ABG may be appropriate in some clinical scenarios.

Association between severe hypoglycemia, adverse macrovascular events, and inflammation in the Edinburgh Type 2 Diabetes Study.

OBJECTIVE: To determine whether a history of severe hypoglycemia was associated with an increased risk of subsequent macrovascular events in people with type 2 diabetes and to explore possible mediation of this association by inflammation. RESEARCH DESIGN AND METHODS: A cohort of 1,066 adults aged 60-75 years with type 2 diabetes was evaluated prospectively. Baseline history of severe hypoglycemia and plasma levels of the inflammatory markers C-reactive protein, fibrinogen, interleukin-6, and tumor necrosis factor-α were recorded. Their association with incident macrovascular events after 4 years was explored. RESULTS: At baseline, 87 participants (8.2%) reported one or more episodes of severe hypoglycemia within the preceding year, and at follow-up 99 participants (9.3%) had suffered a new macrovascular event. Hypoglycemia was associated with increased odds of macrovascular events (odds ratio [OR] 2.11 [95% CI 1.06, 4.21], P = 0.035), including coronary heart events (OR 2.44 [95% CI 1.13, 5.26], P = 0.023), largely due to increased myocardial infarction (OR 4.02 [95% CI 1.54, 10.48], P = 0.004). Hypoglycemia was also associated with increased levels of inflammatory markers, including a general inflammation factor derived using principal-components analysis (P = 0.030, after adjustment for cardiometabolic risk factors). However, the significant association between hypoglycemia and macrovascular events persisted after adjustment for inflammatory markers. CONCLUSIONS: The odds of suffering a macrovascular event were higher in patients with type 2 diabetes who had a history of severe hypoglycemia. There was no evidence that a proinflammatory state had a major role in mediating this association.