A systematic review 1 including 39 studies for estimating correlation between pulse oximetry and blood gas analysis, and 23 studies for calculating bias and precision estimates, was abstracted in DARE. The mean correlation (unweighted) was 0.910, and the weighted mean correlation was 0.895. The lowest correlation was observed for critically ill patients (0.760). Data showed substantial differences in bias and precision between pulse oximeters at low saturation, the most common being an underestimation of saturation and falling precision. There was a tendency to overestimate oxygen saturation with increasing carboxyhaemoglobin concentration, skin pigment, hyperbilirubinaemia. Readings from finger probes were more accurate than from ear probes. The authors conclude that pulse oximeters may fail to record accurately the true oxygen saturation during severe or rapid desaturation, hypotension, hypothermia, dyshaemoglobinaemia and low perfusion states.
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