Physiology

Question 1

How do you calculate the anion gap?

Answer 1

(Na + K) - (Cl + HCO3)

Question 2

What are the causes of normal anion gap metabolic acidosis?

Answer 2

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

Question 3

What are the causes of raised anion gap metabolic acidosis?

Answer 3

1. Lactic acidosis (shock, hypoxia, metformin)
2. Ketoacidosis (DKA, alcohol)
3. Uraemia (renal failure)
4. Acid poisoning (salicylates, methanol)

Question 4

What are the causes of metabolic alkalosis?

Answer 4

(Usually rise in bicarbonate levels)

1. Vomiting
2. Diuretics
3. Hypokalaemia
4. Primary hypoaldosteronism
5. Cushing’s syndrome

Question 5

What is the relationship between Na and K in metabolic alkalosis?

Answer 5

Activation of RAAS –> aldosterone causes Na resorption in exchange for H in DCT kidney