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Low pO2 Contributes to Potential Error in Oxygen Saturation Calculations Using a Point-of-Care Assay
Ian L Gunsolus1, Sara A Love1,2, Louis P Kohl3
1Department of Laboratory Medicine and Pathology.
Objectives:
The present study addressed the accuracy of calculated oxygen saturation (sO2) using point-of-care (POC) testing compared with measured values on a blood gas analyzer.
Methods:
In total, 3,323 sO2 values were measured in 1,180 patients using a CO-oximeter (ABL 800 Flex; Radiometer, Copenhagen, Denmark). Measured parameters were then used to calculate an expected sO2 for the POC method (Abbott i-STAT; Abbott POC, Princeton, NJ). Cases in which calculated sO2 differed from measured sO2 by 10% or more were analyzed.
Results:
Of the 3,323 comparisons performed, 260 (8%) showed discrepancies (± ≥10%) between measured and calculated sO2 values. Ninety-four of discrepant measurements (245 of 260) occurred when pO2 was less than 50 mm Hg. pH and bicarbonate distributions shifted to lower values in discrepant vs nondiscrepant cases.
Conclusions:
Our results suggest that the likelihood of discrepant sO2 is 27% among patients with pO2 less than 50 mm Hg. Direct measurement of sO2 by CO-oximetry is strongly suggested in this clinical scenario.
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