Cyanosis often more evident on lips and nail beds may be present with rest or with exertion. Clinically recognizable cyanosis indicates the presence of more than 5 g reduced Hb/dl of blood. The absolute amount of desaturated Hb determines the presence of cyanosis, a child with polycythemia may appear cyanotic at higher SaO2 than a normothermic or anaemic child. For example, consider three patients with plasma Hb 10,15 & 20 g/dl. Cyanosis (5g reduced Hb/dl present) would not be detectable clinically until O2 saturation reached 50%, 67% & 75% respectively.
Tachycardia and tachypnoea are effective compensatory mechanisms usually present. Clubbing present. Cyanotic children are often small for date due to feeding difficulties. Elevation of patient's red cells mass helps to maintain adequate peripheral oxygen delivery but increase blood viscosity hence a risk of cerebral and renal thrombi.…
