Metabolic acidosis

Question 1

What is an ABG likely to show in metabolic acidosis?

Answer 1

• oxygenation (PaO₂): likely to be normal/ upper limit
• pH: lower than normal indicating acidosis
• PaCO₂: normal/low, respiratory compensation. may mask severity of acidosis
• HCO₃^-: low in keeping with metabolic acidosis

Question 2

What measurement on the ABG can be used to classify metabolic acidosis?

Answer 2

Anion gap

Question 3

How is the anion gap calculated?

Answer 3

(Na⁺ + K⁺) - (HCO₃^- + Cl^-)

Question 4

What is the normal range of the anion gap?

Answer 4

10-18 mmol/L

Question 5

What type of metabolic acidosis is indicated by a normal anion gap?

Answer 5

hyperchloraemic metabolic acidosis

Question 6

What are 5 examples of causes of metabolic acidosis with a normal anion gap (i.e. hyperchloraemic metabolic acidosis)?

Answer 6

1. GI bicarbonate loss: diarrhoea, ureterosigmoidostomy, fistula
2. Renal tubular acidosis
3. Drugs e.g. acetazolamide
4. Ammonium chloride injection
5. Addison’s disease

Question 7

What are 4 causes of metabolic acidosis with a raised anion gap?

Answer 7

presence of added acid:

1. Lactate: shock, sepsis, hypoxia
2. Ketones: diabetic ketoacidosis, alcohol
3. Urate: renal failure
4. Acid poisoning: salicylates, methanol

Question 8

What are the 2 groups that metabolic acidosis secondary to high lactate levels may be subdivided into?

Answer 8

1. Lactic acidosis type A: sepsis, shock, hypoxia, burns
2. Lactic acidosis type B: metformin