Cyanosis NOT improving with 100% oxygen in case of:

Answer is D (Tetralogy of Fallot (TOF): Presence of cyanosis that does not improve with supplemental oxygen suggest true pathological cardiac or pulmonary shunting of blood. Presence of a cyanotic hea disease with an active right to left shunt (Tetralogy of Fallot) is a characteristic cause for failure of improvement with 100% oxygen supplementation. This occurs because desaturated blood in TOF shunts directly from the right (deoxygenated) side of the hea to the left side (systemic) of the hea by passing the lungs where oxygenation occurs.