Last Updated on September 3, 2023
Cyanosis is a bluish discoloration of the nails, skin, and/or mucosa. The term is derived from the Greek word cyanos which means dark blue.
It manifests due to the increased amount of reduced hemoglobin. Hemoglobin is involved in the transportation of oxygen from the lungs to the tissues.
Thus high levels of deoxygenated hemoglobin within the superficial vessels [dermal capillaries and subpapillary venous plexus] cause this bluish appearance.
It must be noted that cyanosis is a manifestation of some underlying condition and not a disease itself. Though the bluishness warrants immediate correction for it can be dangerous if unchecked, the underlying conditions should be looked for and managed as well, wherever feasible.
The bluishness is best seen where the overlying epidermis is thin and the area has a rich network of blood vessels. These are
- Lips
- Tip of the nose
- Cheeks
- Ears
- Oral mucous membranes
The bluishness is more likely to be seen in lighter skins.
Why Does Bluishness Occur? – Mechanism and Significance
In the lung, oxygen attaches to it and it becomes oxygenated hemoglobin or oxyhemoglobin. This oxygenated blood gives a red appearance. In the tissues, oxygen is given out and hemoglobin is now without oxygen, called unoxygenated hemoglobin deoxyhemoglobin, or reduced hemoglobin (RHb).
An amount of reduced hemoglobin of more than 5 gm% in capillary blood would show symptoms of cyanosis.
An adult on average has about 15 gm % of hemoglobin. About 95 percent of this is oxygenated and 5 percent is unoxygenated or reduced.
When this blood goes to capillaries, tissues take up the oxygen, and unoxygenated hemoglobin increases. Usually, only 2-3 gm% is reduced hemoglobin, and the color of the skin and mucous membranes is pink.
But when the amount of reduced hemoglobin exceeds 5 gm% in the capillaries, the blood appears dark, giving the tissues a bluish hue.
This roughly translates into 3.4 g/dL of reduced hemoglobin in arterial blood and roughly correlates with around 80 percent of oxygen saturation [a measure of how much hemoglobin is bound to oxygen] of the blood.
In a similar condition, a patient with lesser hemoglobin levels, say 9 g% because overall available hemoglobin is quite less, the oxygen saturation must reach 65% or less to have 5gm% of reduced hemoglobin.
That simply implies that in patients with moderate to severe anemia cyanosis occurs late and may not occur until the oxygen saturation levels have dropped to critical levels.
Other manifestations of hypoxemia like respiratory symptoms and mental status changes may appear earlier than cyanosis in patients with anemia. In severe anemia, even the patient may die of hypoxemia without manifestation of bluishness.
Types of Cyanosis
- Peripheral
- Bluish discoloration of the hands and feet
- Due to decreased peripheral blood flow.
- Central
- Bluishness all over the body
- Noticed at lips, tongue, and sublingual region clearly [below tongue]
- Mixed
- Manifests as both central and peripheral bluishness
- Cyanosis due to abnormal pigments
- A type of central cyanosis due to abnormal pigments in the blood
Causes
Central
- High altitude
- Impaired lung function
- Severe pneumonia
- Pulmonary embolism
- Chronic obstructive lung disease
- Anatomical shunts cause venous blood to mix with arterial
- Fallot’s tetrad
- Pulmonary arteriovenous malformations
- Multiple intrapulmonary shunts
- Hemoglobin abnormalities
- Hemoglobin with low oxygen affinity
- Altered state of hemoglobin
- Methemoglobinemia
- Sulfhemoglobinemia
- Carboxyhemoglobinemia
- Drug overdose
- Narcotics
- Benzodiazepines
- Sedatives
- Toxins
- cyanide
Peripheral
All conditions that cause central cyanosis are also the causes of peripheral cyanosis.
Other causes are
- Reduced cardiac output
- Heart failure
- Shock
- Exposure to cold [Hypothermia]
- Raynaud’s phenomenon
- A disorder that causes your blood vessels to narrow.
- Decreased blood volume leading to the redistribution of blood flow from extremities
- Arterial or venous obstruction
Mixed
- Acute left ventricular failure
- Mitral stenosis
Abnormal Pigments
Some substances convert hemoglobin into forms that are abnormal and do not bind to oxygen.
Methemoglobinemia
- Normal hemoglobin has iron in ferrous form. In methemoglobinemia, iron is in the ferric form. Methemoglobin is designated as MHb.
- Few substances that cause Hb to MGb conversion
- Nitrates
- Sulfonamide
- Aniline dyes oxidize
- MHb gets immediately reduced back to Hb but a deficiency of diaphorase I increases MHb circulation.
Sulfhemoglobin
SHb is an abnormal sulfur-containing substance that is not normally present in the blood but is formed by the toxic action of drugs and chemicals like
- sulphonamides
- phenacetin
- acetanilide.
SHb forms an irreversible change in the Hb pigment that has no capacity to carry oxygen.
Special Situations
Differential Cyanosis
It is the term used for conditions where cyanosis is present in certain parts and absent in others. it is seen in patent ductus arteriosus and its different presentation in conjuction with other conditions. Depending on that, cyanosis can occur in
- Lower limbs only
- Upper limbs only
- Cyanosis of left upper and both lower limbs
Pseudocyanosis
Pseudocyanosis is the term used when there is a bluish tinge to the skin and/or mucous membranes but there is no hypoxemia or peripheral vasoconstriction.
It should be considered when there is no heart or lung disease and the skin does not blanch under pressure.
It can be caused by
- Metals ingestion
- Silver
- Lead
- Drugs
- Phenothiazines
- Amiodarone
- Chloroquine hydrochloride
When Cyanosis Does not Occur inspite of Decreased Oxygen Levels
- Severe anemia
- The critical amount of hemoglobin is not reduced inspite of saturation
- Other life threatening symptoms may develop before it occurs
- In carbon monoxide poisoning, carboxy-hemoglobin prevents reduction of oxyhemoglobin and the former has a cherry red color. Hence there is no cyanosis.
Presentation and Evaluation
Cyanosis is not a diagnosis or disease in itself. Rather, it is the manifestation of some underlying disorder or condition. The evaluation begins with clinical history and examination and then moves to investigation to reach the conclusion of the cause.
Presentation of the condition may indicate the probable causes.
- A central cyanosis is more likely to be due to heart or lung disease in adults
- In the early prenatal period, it indicates the presence of a congenital heart or lung condition
- Examine if a shock is present
- Low blood pressure
- Increased heart rate
- Increased breathing rate
- low volume pulse
- Any history of exposure
- Ssulfur-containing drugs
- Topical anesthetic agents
- Cold
- Any previous instance
Best places to look for cyanosis
- Cheeks
- Nose
- Ears,
- Oral mucosa
- Nails of hand and feet
A thorough evaluation of the heart and lungs should be done.
Diagnosis of Cyanosis
Clinical assessment of hypoxemia is not reliable. Therefore a patient with cyanosis should be thoroughly investigated.
- Arterial Blood Gases
- Measure oxygen and carbon dioxide levels in blood besides other parameters
- Will reveal the presence of hypoxemia
- Pulse oximetry
- Non-invasive way to know and monitor oxygen levels
- Gives false readings in methemoglobinemia
- Pulse co-oximetry is a better tool when abnormal hemoglobin is suspected
- Complete Blood Count –
- Hemoglobin level is increased with chronic cyanosis.
- White cell count is increased in pneumonia and pulmonary embolism.
- ECG to rule out cardiac abnormalities.
- Chest X-ray can rule out
- Pneumonia
- Pulmonary infarction
- Cardiac failure.
- Ventilation-perfusion scan or pulmonary angiography to rule out pulmonary causes
- Echocardiography for cardiac defects.
- Hemoglobin spectroscopy to look for methemoglobinemia and sulfhaemoglobinaemia.
- Digital subtraction angiography to rule out acute arterial occlusion.
- Duplex Doppler or venography to find acute venous occlusion.
Management
Cyanosis indicates abnormally low oxygen in the blood. Therefore, this requires immediate attention. Oxygen can be given by the regular nasal cannula or high-flow nasal cannula.
In severe cases, assisted ventilation may be required.
and in some instances, assisted ventilation might be required to provide adequate respiratory support Along with this, electrolytes and metabolites should be corrected as well. For generalized cyanosis, the patient should be put on supplemental oxygen. If cyanosis involves only a single limb or hand/foot, this is often due to occlusion of the vessels, and accordingly, appropriate measures should be taken.
Treatment of the underlying cause is the actual definitive treatment.
For congenital heart disease – surgical intervention is often needed.
For methemoglobinemia, the standard treatment is methylene blue. This is converted in the body to leucomethylene blue which reduces methemoglobin to normal hemoglobin.
Exposure to toxic metals or drugs should be stopped.
In case of the Raynauld phenomenon, warmng the hands would help.
References
- Martin L, Khalil H. How much-reduced hemoglobin is necessary to generate central cyanosis? Chest. 1990 Jan. 97(1):182-5.
- Bradberry SM. Occupational methemoglobinemia. Mechanisms of production, features, diagnosis, and management including the use of methylene blue. Toxicol Rev. 2003. 22(1):13-27.
- Cyanosis. McMullen SM, Patrick W. Am J Med. 2013 Mar;126(3):210-2. doi: 10.1016/j.amjmed.2012.11.004[Link]