Chart — Acid-Base
Acid-Base Chart
A quick-reference overview of all four primary acid-base disorders. Use this alongside the ABG Foundation Guide and the ABG Practice Tool to build pattern recognition.
Educational use only. This chart supports learning and clinical practice. Clinical decisions require institutional protocols and licensed supervision. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Value Direction Key
Primary Disorders at a Glance
| Disorder | pH | PaCO₂ | HCO₃ | Primary Driver |
|---|---|---|---|---|
| Respiratory Acidosis | ↓ | ↑ | ↔ | CO₂ retention (hypoventilation) |
| Respiratory Alkalosis | ↑ | ↓ | ↔ | CO₂ loss (hyperventilation) |
| Metabolic Acidosis | ↓ | ↔ | ↓ | HCO₃ loss or acid gain |
| Metabolic Alkalosis | ↑ | ↔ | ↑ | HCO₃ gain or acid loss |
Note: ↔ indicates a normal value in an uncompensated disorder. Compensation shifts the secondary value in the same direction as the primary abnormality.
Respiratory Acidosis
Common causes:
- COPD / chronic lung disease
- Opioid or sedative overdose (respiratory depression)
- Neuromuscular disorders (Guillain-Barré, myasthenia gravis)
- Severe asthma or pneumonia
- Sleep apnea (obstructive or central)
- Chest wall injury impairing ventilation
Compensation: Kidneys retain HCO₃ over days to correct pH.
Respiratory Alkalosis
Common causes:
- Anxiety or panic attack
- Pain (increases respiratory rate)
- Fever or sepsis (early)
- Mechanical ventilation overbreathing
- High altitude (compensatory hyperventilation)
- Pregnancy (progesterone drives hyperventilation)
Compensation: Kidneys excrete HCO₃ to lower pH back toward normal.
Metabolic Acidosis
Common causes:
- Diabetic ketoacidosis (DKA)
- Lactic acidosis (sepsis, shock)
- Acute or chronic renal failure
- Diarrhea (HCO₃ lost in stool)
- Aspirin/salicylate toxicity
- Methanol or ethylene glycol ingestion
Compensation: Lungs hyperventilate (Kussmaul breathing) to blow off CO₂, lowering acidity.
Metabolic Alkalosis
Common causes:
- Prolonged vomiting or NG suctioning (loss of HCl)
- Loop or thiazide diuretics (K⁺ and H⁺ loss)
- Hypokalemia
- Excessive antacid use
- Corticosteroid excess / Cushing's syndrome
- Blood transfusions (citrate metabolism)
Compensation: Lungs hypoventilate to retain CO₂, raising acidity back toward normal (limited response).
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with AARC Clinical Practice Guidelines. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →