The red color of our blood is due to a pigment called hemoglobin, which carries oxygen to various parts of the body. In the normal circulation, oxygen-poor (deoxygenated) blood enters the right side of the heart through veins. The heart pumps this dark-red colored blood to the lungs, where the hemoglobin picks up oxygen and becomes bright red in color. This oxygenated blood enters left side of the heart, where it is pumped to the rest of the body tissues through arteries and capillaries. After extraction of oxygen by tissues, oxygen-poor blood is circulated back into the heart by the veins.
Various disease conditions increase the relative concentration of the oxygen-poor blood. When the deoxygenated hemoglobin concentration in the blood exceeds 5g/100ml, the skin and mucus membranes appear bluish in color; this condition is referred to as cyanosis. A patient with anemia may not develop cyanosis even if the oxygen saturation of blood is low, since their overall hemoglobin concentration is also low.
Cyanosis is described as:
► Central Cyanosis: Patient with central cyanosis shows bluish discoloration of mucus membranes like lips, mouth and tongue. In some cases, the fingers and toes appear blue as well, but they are warm in contrast to peripheral cyanosis (described below), where the extremities tend to be cold. In central cyanosis, the blood is not well oxygenated in the lungs and the arteries carry oxygen-poor blood to the tissues. It is more common in brain, lung and heart diseases.
► Peripheral Cyanosis: In this condition, patients have normal hemoglobin-oxygen saturation in the lungs, but have either poor circulation to the limbs or the tissues extract excessive of oxygen from the capillaries. In peripheral cyanosis, fingers, toes and nail beds become cold and appear blue. The tongue is usually of normal color.
► Differential Cyanosis: Differential cyanosis is a condition where the lower limbs appear blue and the upper limbs appear pink. This occurs due to congenital conditions affecting the heart and arteries that result in decreased blood supply to the lower limbs and normal circulation to the upper limbs. Reversed differential cyanosis is a condition where the lower limbs appear less cyanotic than the upper limbs. This again occurs due to anomalies in the blood vessels.
Though cyanosis helps to detect a number of serious health conditions, the ability to appreciate cyanosis is subjective. A direct measurement of the arterial blood oxygen saturation is a more reliable indicator of the oxygen content of the blood as compared to visually estimating the degree of cyanosis.
Various causes for cyanosis are listed below:
Blood Disorders: Blood disorders can cause cyanosis and are diagnosed with the help of blood tests. These include:
► Polycythemia: Polycythemia is a condition where there is increased production of red blood cells by the bone marrow. The high red blood cell content gives a bluish color to the skin and mucus membranes.
► Methemoglobinemia: Methemoglobinemia is a condition where hemoglobin is present as methemoglobin, which has less affinity for oxygen. The condition may be hereditary or a consequence of ingestion of toxic substances. It causes central cyanosis due to a relative increase in deoxygenated blood in the circulation.
Heart Diseases: Patients with heart diseases are often prone to cyanosis. Heart conditions like congenital heart diseases (anomalies in heart and major blood vessels present from birth), heart failure, cardiogenic shock and pulmonary embolism can cause cyanosis. In these conditions, the blood circulation is affected and the tissues are deprived of oxygenated blood. Some features of heart diseases resulting in cyanosis are:
► Congenital heart disease should be ruled out in an infant with cyanosis. Heart sounds may be abnormal in these children.
► Heart failure initially causes peripheral cyanosis; but if fluid accumulates in the lungs, central cyanosis may be present as well.
► Chest pain and breathlessness may be present.
Based on patientís history, physical examination and electrocardiogram (ECG) testing, these conditions are diagnosed.
Lung Disorders: Lung diseases like chronic obstructive pulmonary disease (COPD) and severe asthma are associated with cyanosis due to decreased oxygen transfer to the blood. Other lung conditions like lung infections, pulmonary hypertension, genetic anomalies and lung trauma may cause cyanosis. Some clues that point out to lung disorders as a cause of cyanosis are:
► The cyanosis is of central type.
► The onset of cyanosis is usually sudden.
► Breathlessness is often present, sometimes along with chest pain.
► Fever may be present in case of lung infection
These disease conditions are diagnosed with the help of a complete history, physical examination, and chest x-ray.
Brain Disorders: Brain injury, a bleed in the brain and seizures often cause cyanosis. Certain toxins, over dosage of drugs like morphine and barbiturates, and alcohol act on brain causing respiratory depression, which in turn may result in central cyanosis. The patient presents with bluish tongue and lips, which needs immediate medical attention. Morphine drug abuse in the mother should be ruled out in a baby presenting with central cyanosis.
High Altitude and Cold Temperature: High altitude may result in reduced oxygen saturation of blood, thereby causing central cyanosis. In addition, cold temperature and shock may reduce supply of oxygen-rich blood to the extremities, thus giving rise to a bluish discoloration of the fingers and toes.
Obstruction in Blood Flow to Limbs: An obstruction in blood flow to the limbs occurs in conditions like Raynaud Disease or clots in the arteries and can result in peripheral cyanosis. Similarly, an obstruction in the veins can result in accumulation of deoxygenated blood in the limbs, resulting in cyanosis. Pulses in the limbs may be reduced in case of arterial obstruction, whereas swelling of the limbs may be present in case of venous obstruction.
Frequently Asked Questions (FAQs)
1. Which doctor should I visit in case I suffer from cyanosis?
You should visit your general physician in case you suffer from cyanosis. Your doctor will diagnose the cause of cyanosis based on your history, after examining you and conducting various tests.
2. Why should you consider cyanosis as a serious problem?
Cyanosis is a physical sign of various blood, heart, lung and congenital disorders, which are sometimes life threatening. Hence, it is necessary to evaluate a patient presenting with cyanosis on an emergency basis.