Acid-Base Interpretation Made Simple: The Step-by-Step Method for CMS Aspirants

Step 1: Check pH#

Always start with pH. If pH < 7.35 = acidosis. If pH > 7.45 = alkalosis.

Step 2: Identify Primary Disorder#

Compare pH with PaCO2 (respiratory) and HCO3- (metabolic). The component that moves in the same direction as pH is the primary disorder.

Step 3: Check Compensation#

Check if the compensation is appropriate. Winter's formula is key for metabolic acidosis compensation.

Step 4: Calculate Anion Gap#

Anion Gap = Na+ - (Cl- + HCO3-). Normal: 8-12 mEq/L.

Step 5: Delta Gap / Delta Ratio#

Delta gap = AG - 12. Delta HCO3 = 24 - measured HCO3-. Delta ratio = delta gap / delta HCO3.

Clinical Case Walkthroughs#

Practice with real ABG cases from UPSC CMS previous year papers to master this framework.