Concentration of methemoglobin to appears cyanosis: (PGI June 2007)

Ans. C (1.5 g/dl) "An methemoglobin level of 15% (i.e. 1.5 g/dl) Q is associated with visible cyanosisQ; a level of 70% MHg level is fatal"- Nelson 18th/2033MethemoglobinemiaQ is a condition in which the iron within hemoglobin is oxidized from the ferrous (Fe2+) state to the ferric (Fe3+) state, resulting in the inability to transport oxygen and carbon dioxide. Clinically, this condition causes cyanosis.Methemoglobinemia in children usually results from exposure to : Oxidizing substances nitrates or nitrites, aniline dyes, or medications, indications, including lidocaine, prilocaine, and phenazopyridine hydrochloride.Cyanosis Occurs WhenDeoxygenated hemoglobin (usually in amounts >4 g/dL) orMethemoglobin (>1.5 g/dL) Q orSulfhemoglobin (>0.5 g/dLQ) CYANOSIS | | | Centralcyanosis Peripheralcyanosis # Central cyanosis is caused by in adequate oxygenation of systemic arterial blood due to decreased arterial oxygenQ saturation or Hemoglobin abnormalities# It results from cardiac shunting, pulmonary diseases or hematological disorders (Hb abnormalities)# Central cyanosis is charachterized by cyanosis affective both mucous membranes and skin5 # Peripheral cyanosis is caused by slowing of blood flow and increased extraction of oxygen from normally saturated blood# It results from vasoconstriction or decreased peripheral blood flow, reduced cardiac output or vascular occlusion# Peripheral cyanosis is characterized by cyanosis of skin alone and sparing of mucous membranes*3