Cyanosis

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Cyanosis mechanism and

how to overcome

*Definition*Cyanosis is a blue discoloration of the skin and mucous membranes

Due to:The presence of an abnormally great amount of reduced Hb in the superficial capillaries

Threshold of cyanosis

It is the minimal concentration of reduced Hb In the capillary blood that leads to appearance of cyanosis.

-It’s about 5gm% capillary bloodThreshold cyanosis = 0.5 (reduced Hb in arterial blood + reduced Hb in venous blood).

Cyanosis does not occur in-:

1-anemic hypoxia:-due to decrease hemoglobin content.

2-histotoxic hypoxia:-as smaller amount of reduced hemoglobin present in venous blood

3-co poisoning:-because of cherry red color of carboxy Hb

Cyanosis can be seen in:

In Fingers Ear lobes Nails In lips

causes of cyanosis

1-hypoxic hypoxia

2-Stagnant hypoxia

3-Asphxia

Mechanisms of cyanosis1-Hypoxic hypoxia

-Rate of diffusion of O2 to tissues is decreased.

-O2 tension and O2 content decrease in arterial and venous blood

causes1-Low O2 in inspired air:

a)Breathing air with low O2 content at sea level(e.g. respiration of inert gases)b)High altitudes (lower total atmospheric pressure &then O2 tension)

2-hypoventilationa)Obstruction of air passagesb)Emphysemac)Depression of respiratory center

3-alveo-capillary block: increase of the thickness of the alveo-capillary membrane leads to decrease of diffusion of gases through membrane

4-short circuit between right and left side of the hearta)Patent ductus arteriosusb)Interatrial or interventriclar septal defect

2-stagnant hypoxia -it results from deficiency of blood flow through

tissues-O2 tension & O2 content in arterial blood is normal-O2 tension & O2 content in venous blood decrease

Causes and types-:1-generalized circulatory deficiency : as

congestive heart failure2 -localized circulatory deficiency: as peripheral

vascular spasm (e.g. Reynaud's disease

3-asphyxiaIn which there is both hypoxia and hypercapina

*Types of Cyanosis*

1 -peripheral 2-central

Normal arterial blood saturation) (Low arterial blood saturation

Peripheral cyanosisIt occurs due to localized reduction of

blood flow on exposure to cold, causing capillary vasoconstriction. Also occurs

in reduced cardiac output i.e. Heart failure or Shock. Peripheral cyanosis is

also seen in peripheral vascular disease like Reynaud's disease.

Central cyanosis •This is either due to imperfect

oxygenation of blood in lung or admixture of venous and arterial

blood. It is evident when O2 saturation falls below 80% to 85%.

Differences between central and peripheral cyanosisPeripheral Central Points

*Arterial and venous diseases: Reynaud disease and thrombosis.

*Polycythemia.*cold exposure.

*congestive heart failure.

Cardiac diseases e.g.: congestive heart failure and septal defect.

*Diseases that interfere with ventilation or gas exchange in lung.

.1causes

Localised Generalised .1cyanosis

Cold Warm .Affected part

Disappears Does not disappear Application of warm

Stagnation of the blood in the peripheral circulation.

Blood pumped in the aorta contains more than 5 gm% reduced Hb.

blood

Factors that affect cyanosis:

1-Capillary factors:Factors that increase the number of open capillaries or increase the diameters e.g. (heat – CO2 – acid metabolites) increase the depth of central cyanosis but improve peripheral cyanosis.

2-Skin thickness:Cyanosis is deeper in thin skin areas.

3-Skin pigmentation:It alters whether physiological( e.g. in yellow races) or pathological ( e.g. in jaundice). In dark races cyanosis in the skin is masked

4-Blood composition:The presence of abnormally great amount of Met-Hb produces a cyanotic like colour. Other abnormalities in the blood composition also alter the depth of cyanosis (e.g. leukemia and lipaemia)5-The amount of reduced Hb and oxyHb:Cyanosis becomes deeper if the amount of reduced Hb is increased or the amount of oxyHb is decreased.

Overcoming cyanosis

1-Warming of the affected area:Peripheral cyanosis brought about by exposure to cold or by gentle warming of fingers and toes.

2-Oxygenation as a treatment for cyanosis:Initial stabilization requires .

3-Surgery as a treatment: Treatment of central cyanosis due to congenital

heart disease .

4-Intravenous fluids:Children who have difficulty in feeding due to cyanosis need fluids to be administrated.5-Drugs as a treatment for cyanosis:Drugs are prescribed to reduce the excess accumulation of fluids such as Diuretics

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