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A. A-a Gradientnavigator

  1. Measures difference in alveolar (A) and arterial (a) oxygen concentration
  2. Depends on alveolar interface with pulmonary capillaries
  3. Calculation A-a Gradient ~ [FiO2 x (760-47)-(1.25 x pCO2)] - pO2

B. Shunt and Other V/Q Mismatchnavigator

  1. Pulmonary Embolism
  2. COPD, Asthma (mucus plugging, bronchoconstriction)
  3. Pulmonary Hypertension (effective capillary destruction; reduced DLCO)
  4. Cardiac Shunts
    1. Atrial or Ventricular Septal Defects
    2. Patent Foramen Ovale (PFO)
    3. Patent Ductus Arteriosus (PDA)

C. Impaired Gas Exchange (at alveolar level)navigator

  1. Inflammation: pneumonia
  2. Pulmonary Fibrosis
  3. Sarcoidosis and other infiltrative lung diseases
  4. Alveolar Cell Carcinoma

D. Pulmonary Edemanavigator

  1. Cardiogenic (CHF)
  2. ARDS (non-cardiogenic)

E. Acute Pulmonary Edemanavigator

  1. Ischemia is usual precipitant in patients with pre-existing disease
  2. Acute Mitral Regurgitation: ischemia, infarction
  3. Arrhythmia
  4. Heart Failure systolic and diastolic dysfunction with volume overload
  5. Papillary muscle rupture
  6. Acute Lung Process: ARDS, Diffuse Pneumonia

F. Orthodexia [1]navigator

  1. Decrease in arterial oxygen saturation from recumbent to erect position
  2. Recurrent pulmonary emboli
  3. Chronic lung disease
  4. Liver disease (hepatopulmonary syndrome)
  5. Previous pneumonectomy
  6. Pulmonary arteriovenous malformation (AVM)
  7. Patent foramen ovale (PFO)

Resources navigator

calcAa Gradient

References navigator

  1. Hegland DD, Kunz GA, Harrison JK, Wang A. 2005. NEJM. 353(22):2385 (Case Discussion) abstract