Simple Method of Acid Base Balance Interpretation

A FOUR STEP METHOD FOR INTERPRETATION OF ABGS


Usefulness

This method is simple, easy and can be used for the majority of ABGs. It only addresses acid-base balance and considers just 3 values.


Step 1. Use pH to determine Acidosis or Alkalosis.

   ph

 < 7.35

 7.35-7.45

 > 7.45

 Acidosis

 Normal or Compensated

 Alkalosis


Step 2. Use PaCO2 to determine respiratory effect.

   PaCO2

 < 35  35 -45 > 45
  •  Tends toward alkalosis
  • Causes high pH
  • Neutralizes low pH
 Normal

or

Compensated

  •  Tends toward acidosis
  • Causes low pH
  • Neutralizes high pH

Step 3. Assume metabolic cause when respiratory is ruled out.

 High pH

Low pH

 Alkalosis

Acidosis

 High PaCO2

Low PaCO2

High PaCO2

Low PaCO2

 Metabolic

Respiratory

Respiratory

Metabolic

These steps will make more sense if we apply them to actual ABG values. Click here to interpret some ABG values using these steps. You may want to refer back to these steps (click on "linked" steps or use "BACK" button on your browser) or print out this page for reference.


Step 4. Use HC03 to verify metabolic effect


Please note:


Now, try some patient case studies


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