Arterial blood with an elevated methemoglobin level has a characteristic chocolate-brown color as compared to normal bright red oxygen-containing arterial blood; the color can be compared with reference charts.The SaO2 calculation in the arterial blood gas analysis is falsely normal, as it is calculated under the premise of hemoglobin either being oxyhemoglobin or deoxyhemoglobin. However, co-oximetry can distinguish the methemoglobin concentration and percentage of hemoblobin. At the same time, the SpO2 concentration as measured by pulse ox is false high, because methemoglobin absorbs the pulse ox light at the 2 wavelengths it uses to calculate the ratio of oxyhemoglobin and deoxyhemoglobin. For example with a methemoglobin level of 30-35%, this ratio of light absorbance is 1.0, which translates into a false high SpO2 of 85%. Differential diagnosis
Other conditions that can cause bluish skin include argyria, sulfhemoglobinemia, heart failure,  Amiodarone-induced bluish skin pigmentation and acrodermatitis enteropathica. Treatment
Methemoglobinemia can be treated with supplemental oxygen and methylene blue. Methylene blue is given as a 1% solution (10 mg/ml) 1 to 2 mg/kg administered intravenously slowly over five minutes. Although the response is usually rapid, the dose may be repeated in one hour if the level of methemoglobin is still high one hour after the initial infusion. Methylene blue inhibits monoamine oxidase, and serotonin toxicity can occur if taken with an SSRI (selective serotonin reuptake inhibitor) medicine.Methylene blue restores the iron in hemoglobin to its normal (reduced) oxygen-carrying state.
Tinea faciei is a fungal infection of the skin of the face. It generally appears as a photosensitive painless red rash with small bumps and a raised edge appearing to grow outwards, usually over eyebrows or one side of the face. It may feel wet or have some crusting, and overlying hairs may fall out easily. There may be a mild itch. Treatment
Most infections can be treated with topical antifungal medication. Rarely, more extensive or long-standing infections may require treatment with oral antifungals. The infection will still be contagious between 24 and 48 hours of the first treatment. The ringworm should go away within 4–6 weeks after using effective treatment. See also
Tinea corporis
Antifungal drug
List of cutaneous conditions

References


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