Cyanosis – colloquially called cyanosis – (synonyms: caeruleus disease; ICD-10 R23.0: cyanosis) is the bluish discoloration of the skin and mucous membranes.
One can distinguish true cyanosis from pseudocyanosis. Pseudocyanosis is a bluish or grayish-bluish discoloration of the skin and/or mucous membranes that, unlike true cyanosis, is not due to hypoxemia (reduced oxygen content of the blood) or ischemia (reduced blood flow), but is usually due to pigment deposits. Causes include drug side effects or ingestion of certain metals and metal compounds. Pseudocyanosis is also occasionally used to describe the dark reddish skin changes seen in polycythaemia vera (PV). The following forms of true cyanosis can be distinguished:
- Hemoglobin cyanosis
- Central cyanosis results from decreased oxygenation (oxygenation) of the blood (that is, bluish discoloration of the skin and central mucous membranes). Two forms of central cyanosis can be distinguished:
- Pulmonary cyanosis (originating in the lungs): impaired ventilation, diffusion, or perfusion (e.g., due to pulmonary emphysema/irreversible hyperinflation of the smallest air-filled structures (alveoli/pulmonary alveoli); this leads to inadequate oxygenation of the blood in the alveoli and capillaries
- Cardiac cyanosis (originating from the heart): e.g., mixing of oxygenated blood in arteriovenous anastomoses, i.e., admixture of venous to arterial blood (e.g., heart defect with right-to-left shunt)
- Peripheral cyanosis – occurs due to increased oxygen depletion in the body periphery (e.g., reduced cardiac output or shock/volume deficiency); blue coloration of the lips and the acras* ; mucous membranes, on the other hand, are rosy!
- Combination of central and peripheral cyanosis.
- Central cyanosis results from decreased oxygenation (oxygenation) of the blood (that is, bluish discoloration of the skin and central mucous membranes). Two forms of central cyanosis can be distinguished:
- Hemiglobin cyanosis (in which pathological hemoglobins are formed, which have a reduced ability of hemoblobin to bind oxygen; here iron is bound in trivalent form, which is not capable of oxygen binding); causes of hemiglobin cyanosis are the occurrence of:
- Carboxyhemoglobin → carboxyhemoglobinemia.
- Methemoglobin → methemoglobinemia
- Sulfhemoglobin → carboxyhemoglobinemia
* When cyanosis affects the acra (fingers, toes, or nose), it is called acrocyanosis.
No figures are available on the prevalence (frequency of disease) and incidence (frequency of new cases) of the above forms.
Course and prognosis: The course and prognosis of central and peripheral cyanosis depends on the underlying disease. Because hemiglobin cyanoses are usually acquired, discontinuation/removal from the area of intoxication (for carboxyhemoglobin, CO intoxication; for methemoglobinemia, e.g., methemoglobin-stimulating drugs; for sulfhemoglobin, e.g., taking phenacetin and sulfonamides) and adequate therapy (for carboxyhemoglobin, e.g., O2 administration) will result in patient recovery.
