ABG Interpretation Made Easy

Normal values

  1. pH: 7.35-7.45
  2. PaCO2: 35-45 mmHg (4.7-6 kPa)
  3. PaO2: 75-100 mmHg
  4. HCO3-: 22-26 mEq/L
  5. SaO2: 94-100%
  6. Base excess: -2 to +2 mmol/L
abg
“Arterial blood for arterial bloog gas analysis” by jlcampbell104 is marked with Public Domain Mark 1.0. To view the terms, visit https://creativecommons.org/publicdomain/mark/1.0/?ref=openverse.

Step 1: pH

  1. >7.45 = Alkalemia
  2. <7.35 = Acidemia
  3. 7.35-7.45 = Normal or Complete compensation

Step 2: pCO2

  1. Increased = Respiratory acidosis or compensation of metabolic alkalosis
    • Determine chronicity by looking at metabolic compensation:
      • Acute: 10 Δ pCO2 = 0.08 Δ pH (opposite direction)
      • Chronic: 10 Δ pCO2 = 0.03 Δ pH
  2. Decreased = Respiratory alkalosis or compensation of metabolic acidosis

Step 3: HCO3-

  1. Increased = Metabolic alkalosis (VOMED) or compensation of respiratory acidosis
  2. Decreased = Metabolic acidosis or compensation of respiratory alkalosis
    • Determine anion-gap (AG): Normal = 5-12 (or 2.5 X Albumin)
      • AG = Na – [Cl – HCO3]
        • AG increased = Anion gap acidosis (MUDPILES/GOLDMARK)
        • AG decreased = Non-anion gap (hyperchloremic) acidosis (GUT/HARDUP)

Step 4: Determine compensation

If there is metabolic acidosis or alkalosis, determine if there is appropriate respiratory compensation:

  1. Expected pCO2 = 1.5 X [HCO3] + 8 +/- 2 (Winter’s formula) OR
  2. Expected pCO2 = last 2 digits of pH

No respiratory compensation: Expected pCO2 = Measured pCO2

Respiratory compensation: Expected pCO2 ≠ Measure pCO2

Step 5: Delta ratio

ΔAG / ΔHCO3

  • 1 = No other derangements
  • >1.5 = Superimposed metabolic alkalosis
  • <0.8 = Superimposed non-anion gap metabolic acidosis

Mnemonics

MUDPILES:

  1. Methanol/Metformin
  2. Uremia
  3. DKA
  4. Paraldehyde
  5. INH
  6. Lactic acidosis
  7. Ethylene glycol
  8. Salicylates

GOLDMARK:

  1. Glycols
  2. Oxoproline
  3. L-lactate (standard lactate seen in lactic acidosis)
  4. D-lactate (exogenous lactate produced by gut bacteria)
  5. Methanol
  6. Aspirin
  7. Renal failure
  8. Ketones (diabetic, alcoholic, starvation)

GUT:

  1. Gastrointestinal losses (diarrhea, pancreatic fistula)
  2. Urinary losses
  3. Total parenteral nutrition

HARDCUP:

  1. Hyperchloremia
  2. Acetazolamide, Addison’s disease
  3. Renal tubular acidosis
  4. Diarrhea, iliostomies, fistula
  5. Cholestyramine
  6. Ureteroenterostomies
  7. Pancreatoenterostomies

VOMED:

  1. Vomiting or aspiration
  2. Overcorrection of chronic hypercarbia or any acidosis
  3. Mineralocorticoid excess
  4. Ethylene glycol poisoning/Early sepsis
  5. Diuretics/Diarrhea


Write your Viewpoint 💬

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.