Cyanosis

What is Cyanosis

With the medical term cyanosis it indicates a bluish-purplish color of skin and mucous membranes, a typical consequence of an "insufficient quantity of oxygen in the blood."

Cyanosis can therefore occur due to circulatory or respiratory disorders, which cause a lowering of oxygen levels in the blood, in particular:

• an excessive concentration of deoxygenated hemoglobin in the blood capillaries, due to a lack of central oxygenation (with a reduction in oxygenated Hb);
• a slowing down of the peripheral circulation (venous stasis), with a consequent increase in the extraction of oxygen from the Hb by the tissues;
• an increase in the concentration of hemoglobin derivatives (such as methemoglobin or sulfohemoglobin) in the capillary bed.

Cyanosis is associated with a variety of conditions, many of which are life-threatening: hypoxia, extreme cooling, obstruction of the airways caused by a foreign object (choking), heart failure, difficulty in respiratory function and cardiopulmonary arrest. In infants, it may be evident as a result of congenital heart defects or respiratory distress syndrome.

Hemoglobin, dermal blood supply and skin color

The color of the skin is determined - as well as by the composition and concentration of two pigments (carotene and melanin) - also by the dermal blood supply. Red blood cells contain hemoglobin (Hb), which binds oxygen to transport it in the body. . The oxygenated Hb takes on a bright red color, which gives the blood vessels in the dermis a pink color, more evident in fair-skinned subjects. In the course of an inflammatory process, that is, when these vessels are dilated, this color becomes more pronounced. Conversely, following a reduction in systemic vascularization, the superficial vessels lose oxygen and the hemoglobin in a reduced (or deoxygenated) form changes color, becoming darker. The skin surface and mucous membranes consequently take on a bluish color and we speak of cyanosis .

Symptoms

Cyanosis is evident in tissues near the surface of the skin, due to low oxygen saturation. In particular, it is easily found at the level of the lips, nail bed, earlobes, cheekbones, mucous membranes and other locations where the skin is particularly thin. Cyanosis may or may not be associated with other symptoms which vary depending on the underlying condition.
Cardiac and respiratory symptoms associated with cyanosis:

• Chest pain;
• Breathing difficulties, including rapid breathing (tachypnea) and shortness of breath (dyspnea);
• Cough with dark mucus.

Other symptoms that can occur with cyanosis:

• Fever;
• Lethargy
• Headache;
• Changes in mental status, including confusion and loss of consciousness, even for a brief moment.

Pathophysiological mechanisms

From the physio-pathogenetic point of view, three mechanisms cause cyanosis:

• Systemic oxygen desaturation: a pulmonary (asthma, COPD, lung cancer ...) or cardiac (various types of heart disease) problem can lead to the "insufficient concentration of oxygenated hemoglobin in the arterial blood (there is little oxygen, therefore a lot of Hb reduced / deoxygenated).
• A slowing of the peripheral circulation, due to circulatory problems (eg varicose veins, atrial fibrillation, right heart failure), can induce an increase in the extraction of oxygen by the peripheral tissues.
• A generalized cyanosis can occur when - as in the course of particular poisonings (ingestion of drugs / toxins or metals, such as silver or lead, carbon monoxide poisoning) - abnormal hemoglobin compounds are formed, such as methemoglobin or sulfohemoglobin.

Based on these causal mechanisms, two main types of cyanosis are described:

• central cyanosis (affects the whole body)
• peripheral cyanosis (affects only the extremities or fingers).

Cyanosis can be limited to only one area of ​​the organism, for example the limbs, and in this case it is related to local disturbances of the blood circulation.

Some dermatological conditions can cause skin discoloration that mimics cyanosis, even in the presence of adequate oxygen levels in the capillary beds.

Cyanosis can also be caused by external factors, such as high altitude (because there is "less oxygen" in the air) or exposure to cold air or water (which induce vasoconstriction).

Central cyanosis

Central cyanosis is often due to a circulatory or pulmonary problem, which leads to poor blood oxygenation. It develops when the concentration of deoxygenated hemoglobin (reduced Hb = non-oxygenated) is equal to or greater than 5 g / 100 ml.

In adults with normal hemoglobin values ​​(13.5-17 g / dL in men, 12-16 g / dL in women), central cyanosis is evident if oxygen saturation is ≤ 85% (coincides with "insufficient saturation of O2 in the blood).

Normally, the concentration of deoxyhemoglobin in venous blood is about 3 g / 100 ml; this value varies depending on the increases or decreases in the total Hb values. Therefore, the critical concentration that causes cyanosis is more easily reached in the course of polyglobulia, that is in subjects with a "high concentration of (absolute) hemoglobin in the blood, and with greater difficulty by patients with anemia (in these subjects the saturation should drop to approximately 60%, before cyanosis becomes evident.) As a result, oxygen deficiency may be more severe in an anemic patient who does not have cyanosis than in a cyanotic patient with high blood hemoglobin.
Possible causes of central cyanosis include:

1. Central Nervous System (alteration of normal ventilation):

• Intracranial hemorrhage;
• Abuse of certain drugs or drug overdose (for example: heroin);
• Tonic-clonic seizure (for example: epileptic attack).

2. Respiratory system:

• Pneumonia;
• Bronchiolitis;
• Bronchospasm (for example: asthma);
• Pulmonary hypertension;
• Pulmonary embolism;
• Pleural effusion;
• Pulmonary fibrosis;
• Hypoventilation;
• Chronic obstructive pulmonary disease (emphysema and chronic bronchitis);
• Upper airway obstruction.

3. Cardiovascular system:

• Congenital heart disease (e.g. tetralogy of Fallot, heart disease with left-right shunt, septal defects, etc.);
• Heart failure;
• Valvulopathies;
• Heart attack;
• Severe hypotension (shock);
• Chronic pericarditis.

4. Other causes:

• Severe methemoglobinemia (overproduction of abnormal hemoglobin);
• Polycythemia;
• Obstructive sleep apnea;
• Reduction of the partial pressure of oxygen in the atmosphere: at high altitudes, cyanosis can develop at altitudes> 2,400 m;
• Hypothermia (prolonged exposure to cold);
• Raynaud's phenomenon (resulting from severe restriction of blood flow to the fingers or toes);
• Acrocyanosis (persistent, painless and symmetrical cyanosis of the hands, feet or face, caused by vasospasm of the small vessels of the skin, in response to cold).

Peripheral cyanosis

In this case, cyanotic patients have normal systemic arterial oxygen saturation, but their peripheral circulation is slowed down (blood stasis in the tissues). Cyanosis can result from an arteriovenous difference in oxygenation, which can lead to an increase in oxygen extraction by peripheral tissues.

All factors contributing to central cyanosis can provoke the appearance of peripheral symptoms; however, peripheral cyanosis can occur even in the absence of cardiac or pulmonary dysfunction.
Causes of peripheral cyanosis include:

• All common causes of central cyanosis;
• Venous hypertension;
• Reduced cardiac output (for example: heart failure, hypovolaemia, etc.);
• Arterial obstruction (for example: peripheral vascular disease);
• Venous obstruction (for example: deep vein thrombosis, thrombophlebitis, etc.);
• Generalized vasoconstriction due to exposure to cold (Raynaud's phenomenon).

Diagnosis

The evaluation of a cyanotic patient involves the following steps:

• History: presence of congenital heart disease, drug intake or exposure to chemical agents (which result in abnormal hemoglobins).
• Medical examination to differentiate central from peripheral cyanosis;
• If the cyanosis is localized to one extremity, evaluate the presence of a peripheral vascular obstruction;
• Evaluation of the presence of hippocratic fingers: sometimes, the combination of "drum rod" phalanges and cyanosis suggests the presence of congenital heart disease and lung disease;
• Blood tests, including: complete blood count, spectroscopic and electrophoretic analysis of hemoglobin (to measure abnormal Hb);
• Chest x-rays
• Electrocardiogram (ECG) to measure the electrical activity of the heart;
• Lung and lung function test.

Treatment

Cyanosis typically indicates that the body is unable to acquire enough oxygen. Treatment of the underlying disease (for example: heart disease or lung disease), or the underlying cause, can restore the appropriate skin color.

In some cases, acute cyanosis can be a symptom of a serious or life-threatening condition, which should be immediately evaluated in an emergency setting. In general, medical intervention should take place within 3-5 minutes.