Acid–Base Disorders: Approach to Arterial Blood Gas (ABG) Interpretation
—Step 1: Determine the pH
pH < 7.35: Acidemia
pH > 7.45: Alkalemia
—Step 2: Identify the primary disorder
↑ PaCO₂ = Respiratory acidosis
↓ HCO₃⁻ = Metabolic acidosis
↓ PaCO₂ = Respiratory alkalosis
↑ HCO₃⁻ = Metabolic alkalosis
—Step 3: In metabolic acidosis, always calculate the anion gap:
Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)
Normal: 8–12 mEq/L
High: >12 mEq/L
—High anion gap metabolic acidosis (HAGMA): Think MUDPILES
Methanol
Uremia
Diabetic ketoacidosis
Propylene glycol
Iron tablets/Isoniazid
Lactic acidosis
Ethylene glycol
Salicylates (late)
—Normal anion gap metabolic acidosis (NAGMA): Think HARDASS
Hyperalimentation
Addison disease
Renal tubular acidosis
Diarrhea
Acetazolamide
Spironolactone
Saline infusion
—Respiratory acidosis: Usually due to hypoventilation
Airway obstruction
COPD/asthma exacerbation
CNS depression (opioids, sedatives)
Neuromuscular weakness
—Respiratory alkalosis: Usually due to hyperventilation
Anxiety/panic attack
Hypoxemia
Pulmonary embolism
Early salicylate toxicity
—Metabolic alkalosis: Common causes include
Vomiting
Loop diuretics
Hyperaldosteronism
Excess alkali (antacids)
Forwarded fromRotators Discussion
July 25, 2026 432 4