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The influence of variables that might affect the accuracy of pulse oximetry (SpO 2 ) recordings in critically ill patients is not well established. We sought to describe the relationship between paired SpO 2 /SaO 2 (oxygen saturation via arterial blood gas analysis) in adult intensive care unit (ICU) patients and to describe the diagnostic performance of SpO 2 in detecting low SaO 2 and PaO 2 . A paired SpO 2 /SaO 2 measurement was obtained from 404 adults in ICU. Measurements were used to calculate bias, precision, and limits of agreement. Associations between bias and variables including vasopressor and inotrope use, capillary refill time, hand temperature, pulse pressure, body temperature, oximeter model, and skin colour were estimated. There was no overall statistically significant bias in paired SpO 2 /SaO 2 measurements; observed limits of agreement were +/-4.4%. However, body temperature, oximeter model, and skin colour, were statistically significantly associated with the degree of bias. SpO 2 <89% had a sensitivity of 3/7 (42.9%; 95% confidence intervals, CI, 9.9% to 81.6%) and a specificity of 344/384 (89.6%; 95% CI 86.1% to 92.5%) for detecting SaO 2 <89%. The absence of statistically significant bias in paired SpO 2 /SaO 2 in adult ICU patients provides support for the use of pulse oximetry to titrate oxygen therapy. However, SpO 2 recordings alone should be used cautiously when SaO 2 recordings of 4.4% higher or lower than the observed SpO 2 would be of concern. A range of variables relevant to the critically ill had little or no effect on bias.

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