Summary of Acid-Base Disturbances
| pH (7.3 – 7.4) | H+ | HCO3 (22-26) | pCO2 (34-45) | K+ | |
| metabolic acidosis | ↓ | ↑ | ↓ | ↓↓↓ | ↑ |
| metabolic alkalosis | ↑ | ↓ | ↑ | ↑↑↑ | ↓ |
| respiratory acidosis | ↓ | ↑ | ↑↑↑ | ↑ | ↑ |
| respiratory alkalosis | ↑ | ↓ | ↓↓↓ | ↓ | ↓ |
Multiple arrows means it is a compensatory mechanism.
- PCo2 is usually 1.5 times the bicarb + 8, if it’s higher it’s compensated
- Gap = Sodium – (Cl + Bicarb) = normal is 6-12, greater than 12 is metabolic acidosis
- Normal respiratory rate is 12-20
Acidosis: pH < 7.38
- PCO2 < 38 – metabolic acidosis with respiratory compensation. “Hyperventilation” compensates (blowing off carbon dioxide, which is an acid), decrease in bicarb
- PCO2 38-42 – pure metabolic acidosis
- PCO2 > 42 – primary respiratory acidosis. Need bicarb to say if primary metabolic acidosis (HCO3 < 24) or compensated respiratory acidosis (HCO3 > 28).
Alkalosis: pH < 7.42
- PCO2 <38 – primary respiratory acidosis. Need bicarbonate to see if the patient has primary metabolic acidosis too (HC03 > 28)
- PCO2 38-42 – primary alkalosis without respiratory compensation
- PCo2 > 42 – primary metabolic acidosis with respiratory compensation
Causes of Anion Gap Acidosis:
- MUDPILES – methanol, uremia, diabetic ketoacidosis, paraldehyde, iron, isoniazid, inhalants, lactic acidosis, ethylene glycol (the propylene glycol in lorazepam can cause it too), ethanol and salicylates
- or MULEPAKS: methanol, uremia, lactic acidosis, ethylene glycol, paraldehyde, aspirin, ketoacidosis, starvation
How to work an acid-base problem:
- Assess pH (acid or base)
- Determine if it’s respiratory or metabolic (pCO2 and HCO3)
- Calculate anion gap (can help determine cause).