Cyanosis cannot occur in severe anaemia because
Cyanosis seen when deoxygenated hb >4 gm. so in severe anemia where HB less than 4 gm we cannot see cyanosis.
Anaemic blood has a higher O2 carrying capacity per gram of Hb
It requires a critical concentration of reduced Hb in blood
Patient improves his alveolar oxygen as a compensation for anaemia
There is an increased blood flow through the skin
Respiratory system