Low O2 saturation that does not respond to supplemental O2 - Key diagnostic feature (sat < 85% w/o response to 100% FiO2) - Wavelength averaging by the pulse oximeter causes a falsely low O2 reading - Since there is no true decrease in O2 saturation, there will be no response to 100% FiO2 Severity of symptoms correlates closely to MetHb level and severity of impaired O2 delivery Symptoms will be worse for any MetHb level in patients with baseline impairment of O2 delivery (i.e. CHF, pneumonia, COPD, anemia) #Diagnosis #Toxicology #Methemoglobinemia #Concentrations #Signs #Symptoms
