Differential diagnosis of acid base disorders
1. High Anion Gap Metabolic Acidosis
| C | Carbon Monoxide, Cyanide |
| A | Alcohol, Alcoholic Ketoacidosis |
| T | Toluene |
| M | Metformin, Methanol |
| U | Uraemia |
| D | Diabetic Ketoacidosis |
| P | Paraldehyde, Phenformin, Paracetamol, Propylene glycol |
| I | Iron, Isoniazid |
| L | Lactic acidosis (any cause) |
| E | Ethylene glycol |
| S | Salicylates |
2. Causes of Lactic Acidosis
| Type A: Imbalanced oxygen supply and demand | Type B: Metabolic derangement |
|
Carbon monoxide Shock Severe anaemia Severe hypoxia Excessive oxygen demand: Fever, seizure, exercise, shivering |
B2 agonists Cancer Cyanide Ethanol Hepatic failure Ketoacidosis Metformin / Phenformin Sepsis Thiamine deficiency Inborn errors of metabolism |
3. Non-anion Gap Metabolic Acidosis
| U | Ureteroenterostomy |
| S | Small bowel fistula |
| E | Extra chloride, Normal saline hydration |
| D | Diarrhoea |
| C | Carbonic anhydrase inhibitors (acetozolamide, topiramate etc) |
| A | Adrenal insufficiency |
| R | Renal tubular acidosis |
| P | Pancreatic fistula |
4. Causes of a low anion gap
| Increased cations | Calcium, magnesium, lithium, multiple myeloma |
| Decreased anions | Dilution, hypoalbuminaemia |
| Artefactual | Bromism, Iodism, Propylene glycol, Triglycerides |
5. Metabolic Alkalosis
| C | Contraction (volume contraction) |
| L | Licorice, diuretics |
| E | Endocrine (Hyperaldosteronism, Bartter’s, Cushing’s, Conn’s) |
| V | Vomiting, NG suction (chloride loss) |
| E | Excess alkali (antacids, dialysis, milk-alkali syndrome) |
| R | Refeeding alkalosis |
| R | Renal bicarbonate retention (Hypochloraemia, Hypokalaemia, Chronic hypercapnia) |
6. Respiratory acidosis
| Acute | Chronic |
|
Airway obstruction Aspiration Bronchospasm CNS depression Muscle weakness Pulmonary disease |
Chronic lung disease Neuromuscular disorders Obesity |
7. Respiratory alkalosis
| C | CNS disease (Raised ICP) |
| H | Hypoxia (Altitude, anaemia, VQ mismatch) |
| A | Anxiety |
| M | Mechanical hyperventilation |
| P | Progesterone, pregnancy |
| S | Sepsis, Salicylates and other toxins (nicotine, xanthines) |
