Cyanosis

Definition: A bluish discoloration of the skin, mucous membranes, and nail beds resulting from an increased amount of reduced hemoglobin or of abnormal hemoglobin pigments in the blood and in the tissues of those areas. Cyanosis becomes apparent at a mean capillary concentration of 4 gm/dL reduced Hb, 1.5 methHb, or 0.5 g sulfHb per 100 mL. Cyanosis may not be seen in severely anemic patients because the absolute amount of reduced Hb is small. Conversely, Pts with marked polycythemia will be cyanotic at higher levels of arterial O2 saturations than patients with normal Hb states.

Peripheral cyanosis:

- Vasoconstriction: exposure to cold
- Low cardiac output: CHF, shock
- PVD: arterial obstruction (embolus); arterial constriction (Raynaud's phenomenon); venous obstruction
- Acrcyanosis
- Livedo reticularis

Central cyanosis:

- High altitude
- alveolar hypoventilation, V/Q mismatch
- R - L shunts - TOF, PDA, pulmonary AV fisutlae, multiple small intrapulmonary shunts
  - R-L shunt volume >25% of LV output. Eisenmenger's syndrome.
- Hb abnormalities: methHb, Sulf-Hb
  - Iatrogenic causes of Meth-Hb: acetanalid, phenacetin, benzocaine, lidocaine, nitrites, nitrates, primaquine, nitroprusside, quinones, sulfathiazole

- Cyanosis present since birth is usually due to congenital heart disease.
- Massage or gentle warming of a cyanotic extremity will increase peripheral blood flow and abolish peripheral, but not central, cyanosis.
- The presence or absence of clubbing of the digits should be ascertained. The combination of cyanosis and clubbing is frequent in patients with congenital heart disease and R-L shunting, and is seen occasionally in Pts with pulmonary disease such as lung abscess or pulmonary arteriovenous fistulae. Peripheral cyanosis or acutely developing central cyanosis is not associated with clubbed digits.
- PaO2 and SaO2 should be determined.
- In cyanosis with obscure causes, spectroscopic examination of blood performed to look for abnormal types of Hb.