Thursday, May 3, 2012

A-a gradient

A- Alveolar pO2
a-Arterial pO2
A= 150-1.2(pCO2)

A-a gradient: (normal is 5 to 15)
What is the difference in the amount of oxygen getting into the lungs and that getting from the lungs into the blood?
Answer= A-a gradient
Higher if there's :
Impaired diffusion at alveolar level e.g pulmonary edema,  thickened alveolar membrane 
Abnormal ventilation/perfusion ratio :
  • Decreased alveolar perfusion (shunt)-Pulmonary embolus
  • Decreased alveolar ventilation (dead space)- obstructive diseases, ARDS (Atelectasis/alveolar collapse)
Right to left shunt (blood by passes the alveoli, goes straight back to left side of the heart without getting oxygenated)


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