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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