Cyanosis

Basics

Description

Abnormal bluish discoloration of the skin or mucous membranes

Caused by abnormal elevations of deoxygenated hemoglobin or hemoglobin derivatives in the capillaries:
- Deoxygenated hemoglobin >5 g/dL
- Methemoglobin >1.5 g/dL
- Sulfhemoglobin >0.5 g/dL
The absolute amount of deoxygenated hemoglobin is the pigment that creates the bluish tint:
- The amount of oxyhemoglobin does not affect the blood's color
- Cyanosis is more common in patients with polycythemia and less common in patients with anemia
Cyanosis varies based on skin thickness or pigment
Accumulation of deoxygenated hemoglobin may be systemic producing central cyanosis or localized producing peripheral cyanosis
- Central cyanosis:
  - Hypoxemia
  - Anatomic right to left shunts
  - Abnormal hemoglobin derivatives
- Peripheral cyanosis:
  - Tissue extracts more than normal amounts of O₂ from the blood
  - Hypoperfusion
  - Vasoconstriction to cold air or water
  - Arterial insufficiency
  - Venous insufficiency
  - Acrocyanosis: Painless, symmetrical, cyanosis in distal parts of body, the pathophysiologic cause of which is not known

Etiology

Central cyanosis:

Upper airway obstructive causes
Impaired pulmonary function:
- Hypoventilation:
  - Pneumonia
  - Chronic obstructive pulmonary disease
  - Pulmonary edema
  - Chest wall trauma limiting pulmonary exchange
- Ventilation/perfusion mismatch:
  - Asthma
  - Pulmonary embolus
- Diffusion problems:
  - Interstitial lung disease
  - Anatomic shunts
- Pulmonary arteriovenous fistula:
  - Hereditary hemorrhagic telangiectasia
- High-altitude related, with decreased atmospheric pressure at 16,000 ft
- Decreased inspired oxygen house fire/poison gas
Cardiac abnormalities with right to left shunt:
- Eisenmenger syndrome:
  - Pulmonary hypertension
  - Longstanding intracardiac shunt (VSD, patent ductus arteriosus, ASD)
  - Reversal of flow through detected when pulmonary artery pressure exceeds threshold
Abnormal hemoglobin:
- Low-oxygen affinity hemoglobin mutants:
  - Hb Kansas
  - Hb Beth Israel
  - Hb St. Mande
- Congenital methemoglobinemia:
  - Cytochrome b5 reductase deficiency
  - Hemoglobin M disease
- Acquired methemoglobinemia:
  - Aniline dyes
  - Chloroquine, primaquine
  - Dapsone
  - Local anesthetic agents such as lidocaine
  - High doses of methylene blue
  - Naphthalene
  - Nitrites, nitroglycerine
  - Sulfonamides
  - Fava beans
- Sulfhemoglobin:
  - Generally benign
  - Irreversible alteration of hemoglobin
  - Caused by many medications
  - Dimethyl sulfoxide
  - Paint
  - Phenacetin
  - Phenazopyridine
  - Phenylenediamine
  - Phenylhydroxylamine
  - Sulfanilamide
  - Sulfapyridine
  - Sulfathiazole
  - Sulfur compounds

Peripheral cyanosis:

Shock
Exposure to cold
Arterial insufficiency
Venous insufficiency
Raynaud phenomenon
Acrocyanosis

Pediatric Considerations

Cardiac:
- Cyanotic congenital defects:
  - Tetralogy of Fallot
  - Transposition of great vessels
  - Truncus arteriosus
  - Pulmonary and tricuspid atresia
  - Ebstein anomaly
  - Pseudocoarctation
  - Patent ductus arteriosus
- Total anomalous pulmonary venous return
Pulmonary stenosis:
- Any right-to-left shunting
Respiratory:
- Upper airway disorders/obstruction:
  - Croup
  - Bacterial tracheitis
  - Epiglottitis
  - Retropharyngeal abscess
  - Foreign body
- Lower airway disorders:
  - Asthma
  - Bronchiolitis
  - Pneumonia
  - Cystic fibrosis
  - Pulmonary edema/CHF
  - Pulmonary embolism
Neurologic:
- Breath holding

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