Cyanosis

This presentation is about the causes and mechanisms of central and peripheral cyanosis. It also contain some general information about different scenarios of cyanosis.

1. Cyanosis T he causes and mechanisms of central and peripheral cyanosis

2. Definition Cyanosis is defined as a bluish discoloration of the skin and mucous membranes, resulting from an increased amount of reduced hemoglobin (more than 5 g/ dL ), or of hemoglobin derivatives in the capillary blood. Smaller concentrations of methaemoglobin and sulphmethaemoglobin (1.5 and 0.5 g/ dL , respectively) may also evoke cyanosis. Cyanosis is most marked in the lips, nail beds, ears and malar eminences.

3. Types of Cyanosis and their Mechanisms Cyanosis can be subdivided into two Central cyanosis Peripheral cyanosis. Central cyanosis is due to decreased arterial oxygen saturation (most of the cases) or the presence of an abnormal hemoglobin derivative (rarely). Peripheral cyanosis is due to slowing of blood flow to an area, resulting in greater extraction of oxygen from normally saturated arterial blood. This results from vasoconstriction or diminished peripheral blood flow (reduced cardiac output).

4. Causes Central cyanosis Peripheral cyanosis • Due to decreased arterial oxygen saturation • Cardiac causes Fallot's tetralogy Eisenmenger's syndrome Congestive cardiac failure • Pulmonary causes Chronic bronchitis Interstitial lung disease Pulmonary arteriovenous fistula • High altitude • Cirrhosis of liver • Due to abnormal hemoglobin derivatives • Methaemoglobinaemia • Sulphaemoglobinaemia •Due to diminished peripheral blood flow resulting from reduced cardiac output • Mitral stenosis • Congestive cardiac failure • Shock •Due to local vasoconstriction • Cold exposure • Raynaud's disease • Peripheral vascular disease

5. Differentiation Between Central and Peripheral Cyanosis Feature Central cyanosis Peripheral cyanosis • Site Mucous membranes and skin are both involved Mucous membranes of the oral cavity or those beneath the tongue spared • Tongue Affected Unaffected • Temperature of limb Warm Cold • Clubbing Present(Shunts) Absent • Polycythemia Present(Shunts) Absent • Local warming Cyanosis remains Cyanosis • Breathing pure oxygen for 10 minutes Cyanosis may disappear disappears Cyanosis remains • Arterial blood gas studies Abnormal Normal

6. General Information about Cyanosis Cyanosis in cardiac failure is often of a mixed type due to both central and peripheral causes. "Differential cyanosis" is cyanosis occurring in the lower limbs, but not in the upper limbs. This occurs in patients with patent ductus arteriosus with a reversal of shunt. Cyanosis of only upper limbs can occur in patients with patent ductus arteriosus with reversal of shunt in combination with transposition of great vessels. Cyanosis of left-upper limb and both lower limbs (sparing right upper limb) can occur in patients with patent ductus arteriosus with reversal of shunt in combination with a pre-ductal coarctation of aorta. Intermittent cyanosis in Ebstein's anomaly.