PURPOSE: Signal extraction pulse cooximetry has been used to accurately and instantaneously measure carboxyhemoglobin in a noninvasive manner in hospitals and outpatient settings. This study attempts to clarify issues regarding substances interfering with the signal extraction algorithm software analysis which may result in erroneous values of carboxyhemoglobin being reported.
METHODS: In a pulmonary office in Michigan pulse cooximetry was used for screening of patients for carboxyhemoglobin for a smoking cessation program. A comprehensive history of exposure to carbon monoxide was obtained and a medication list was obtained to help corroborate the carboxyhemoglobin reading.
RESULTS: A patient was found to have a carboxyhemoglobin level of 25% on signal extraction pulse cooximetry. An immediate Arterial blood gas with cooximetry showed a carboxyhemoglobin level of only 1.6%.In addition there was methhemoglobin level of 1.9%.The patient was also taking phenazopyridine (pyridium) which is a Red Azo compound.
CONCLUSION: Substances that have similar absorption spectra in the Red and Infrared spectrum may interfere with noninvasive detection of carboxyhemoglobin by signal extraction pulse cooximetry such as methhemoglobin and pyridium.
CLINICAL IMPLICATIONS: We describe an erroneously high carboxyhemoglobin by pulse cooximetry in the presence of subclinical amounts of methhemoglobin and the drug Phenazopyridine (Pyridium) a commonly used urinary analgesic/antiseptic.Further research must be undertaken to clarify the role of pulse cooximetry for carbon monoxide or carboxyhemoglobin screening and monitoring in a noninvasive manner in the presence of common interfering substances based on absorption characteristics.
DISCLOSURE: Mamatha Reddy, None.