Background: The RAD-57 pulse CO-oximeter is a lightweight device allowing noninvasive measurement of blood carboxyhemoglobin (S(pCO)). We assessed the diagnostic value of pulse CO-oximetry, comparing S(pCO) values from the RAD-57 to standard laboratory blood carboxyhemoglobin (COHb) measurement in emergency department patients with suspected carbon monoxide (CO) poisoning.
Methods: This was a prospective, diagnostic accuracy study according to the Standards for the Reporting of Diagnostic Accuracy Studies criteria in consecutive adult emergency department patients with suspected CO poisoning. S(pCO) was measured with the RAD-57 simultaneously with blood sampling for laboratory blood gas analysis. We made no changes to our standard management of CO poisoning. Blood COHb > 5% for non-smokers, and > 10% for smokers were applied as the reference standard.
Results: We included 93 subjects: 37 smokers and 56 non-smokers. CO poisoning was diagnosed in 26 subjects (28%). The S(pCO) values ranged from 1% to 30%, with a median of 4% (IQR 2.7-7.3%). The COHb values ranged from 0% to 34%, with a median of 5% (IQR 2-9%). The mean differences between the COHb and S(pCO) values were -0.2% ± 3.3% (95% limits of agreement of -6.7% and 6.3%) for the whole cohort, -0.7% (limits of agreement -7.7% and 6.2%) for the non-smokers, and 0.6% (limits of agreement -5.0% and 6.2%) for the smokers. The optimal thresholds for detecting CO poisoning were S(pCO) of 9% and 6% for smokers and non-smokers, respectively.
Conclusions: S(pCO) measured with the RAD-57 was not a substitute for standard blood COHb measurement. However, noninvasive pulse CO-oximetry could be useful as a first-line screening test, enabling rapid detection and management of CO-poisoned patients in the emergency department.
Keywords: CO poisoning; CO-oximetry; carbon monoxide; emergency department; pulse oximetry; sensitivity; specificity.