Your activity: 5 p.v.

Calculator: A-a gradient (alveolar-arterial gradient; AaG)


Calculator: A-a gradient (alveolar-arterial gradient; AaG)

 
Input
 
Age  
Patient temperature  
Elevation  
Percent inspired O2  
pCO2  
Respiratory quotient  
PaO2  

 
Results
 
Important: Inputs must be complete to perform calculation.

 
 
Expected AaG  
Measured AaG  
 
Decimal precision  

 
 

 
Notes
  • High A-a gradients are associated with oxygen transfer/gas exchange problems. These are usually associated with alveolar membrane diseases, interstitial diseases, or ventilation/perfusion (V/Q) mismatch.
  • Hypoxemia in the face of a normal A-a gradient implies hypoventilation with displacement of alveolar O2 by CO2 or other substance.
  • The FiO2 (fraction of inspired oxygen) is equal to the Percent inspired O2/100.
  • In this calculator, pAtm is estimated by elevation above sea level using this formula: pAtm = 760 * eTo(Elevation / -7000).
  • pH2O is dependent on body temperature and calculated with the following formula: pH2O = 47 * eTo((Patient temperature - 37) / 18.4).
  • The equation for expected A-a gradient assumes the patient is breathing room air; therefore, it is less accurate at higher percentages of inspired oxygen.

 
Equations used
 
pAtm = 760 * e(Elevation/-7000)
pH2O = 47 * e((Patient_temperature-37)/18.4)
FiO2 = Percent_inspired_O2 / 100
Expected_AaG = 2.5 + (0.21 * Age)
Measured_AaG = (FiO2 * (pAtm - pH2O)) - (pCO2 / Respiratory_quotient) + (pCO2 * FiO2 * (1 - Respiratory_quotient) / Respiratory_quotient) - PaO2

 

 
Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

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Topic 13447 Version 13.0