METABOLIC ACIDOSIS Flashcards
How do you work out the anion gap? What is the normal range?
(Na + K) - (Cl + HCO3)
Normal 8-12
Why is the anion gap normal when the acidosis is due to loss of bicarbonate?
Body compensates by retaining chloride
Explain how an ion gap occurs in metabolic acidosis even though the HCO3 still falls?
Caused by primary retention of acid rather than primary fall of HCO3
HCO3 still falls but chloride does not go up → this is because retained acids have their own associated anions and these are compensating for fall in HCO3 rather than chloride
An increase in which electrolyte is seen in all non-anion gap metabolic acidoses?
Chloride: Compensates for loss of negative charge caused by HCO3 loss
What is by far the most common cause of a non-anion gap metabolic acidosis? What electrolyte imbalance of this often associated with?
Diarrhoea: Low potassium seen due to loss in stools
Saline infusion: chloride toxicity drives HCO3 out of plasma causing non-anion gap metabolic acidosis
What is the mnemonic for causes of anion gap metabolic acidosis?
MUDPILES
- Methanol
- Uraemia
- Diabetic ketoacidosis
- Propyleneglycol
- Iron tablets or isoniazid
- Lactic acidosis
- Ethylene glycol
- Salicylates
A patient with suspected ingestion of a substance appears confused (possibly inebriated) and complains of visual symptoms. ABG shows a high anion gap metabolic acidosis.
What are they likely to have ingested? Briefly explain pathophysiology and treatment
Methanol
- Found in antifreeze, industrial cleaners, windshield wiper fluid
- Metabolised to formic acid by alcohol dehydrogenase and aldehyde dehydrogenase
- Causes tissue injury: visual loss, confusion, coma + AGMA
- Treatment is to inhibit alcohol dehydrogenase with fomepizole or ethanol
A patient with suspected ingestion of a substance c/o flank pain, oliguria, anorexia (acute renal failure symptoms). ABG shows high anion gap metabolic acidosis.
What are they likely to have ingested? Briefly explain pathophysiology and treatment
Ethylene glycol - found in antifreeze, industrial cleaners, wiper fluid
- Metabolised to glycolate and oxalate by alcohol dehydrogenase: kidney toxins
- Treatment: inhibit alcohol dehydrogenase with fomepizole or ethanol
What substance is a solvent for IV benzodiazepines? Where else is this found? What can overdose cause?
How can you differentiate this from a methanol or ethylene glycol overdose?
Propylene Glycol
- Found in antifreeze as it lowers freezing point of water
- Overdose causes CNS depression, high AG metabolic acidosis, coma, multiorgan failure
- Usually no visual symptoms or nephrotoxicity seen in PG
Someone who is admitted with coma after ingesting an industrial solvent does not have high anion gap metabolic acidosis. What did they like the ingest?
Isopropyl alcohol
What is the cause of a metabolic acidosis in early vs advanced kidney disease? Will they be high or low AG?
- Early: reduction in H+ excretion due to loss of tubule function → normal AG MA
- Advanced: kidneys no longer excrete organic acids leading to retention of urate, phosphate, sulphate etc → high AG MA
What is your top differential for patient presenting with polyuria, polydipsia, abdominal pain and deep and rapid breathing? What is the name of this type of breathing and what is it called by?
Diabetic ketoacidosis
Kussmaul respirations: caused by acidosis
What are the phases of iron poisoning?
what type of metabolic dysfunction does it cause?
- First 6 hours: severe abdominal pain
- 24 hours: cardiac toxicity (shock), coagulopathy, hepatic dysfunction, acute lung injury
- High anion gap metabolic acidosis
People who have a low anion gap often have one of which two conditions?
- Low albumin (important component of anion gap)
- Multiple myeloma (IgG is catatonic and will lower measured positive ions)
Ingestion of which substance would cause inebriation, anion gap metabolic acidosis with damage to retina and optic nerve?
Methanol
