Electrolyte disturbances

Question 1

What are the body fluid compartments?

Answer 1

42L water
28L 35% intracellular fluid
9.4L 12% extracellular fluid
4.6L 4-5% plasma

Question 2

What are the causes of hyponatraemia?

Answer 2

Hypervolaemia:
Heart failure, liver failure, hypoalbuminaemia
Normovolaemia:
Hypothyroidism, hypokalaemia, SIADH
Hypovolaemia:
Vomiting, diarrhoea, haemorrhage, burns, pancreatitis
Hyperglycaemia, uraemia, diuretics, renal artery stenosis, recovery ATN, tubulointerstitial renal disease

Question 3

How are serum levels of potassium controlled?

Answer 3

80-150mmol daily
Uptake of K+ into cells
Renal excretion- controlled by aldosterone
Extrarenal losses- GI

Question 4

What is hypokalaemia?

Answer 4

<3.5

Question 5

What causes acidosis with a normal anion gap?

Answer 5

Gastrointestinal bicarbonate loss: diarrhoea, Ureterosigmoidostomy, fistula
Renal tubular acidosis
Drugs: e.g. acetazolamide
Ammonium chloride injection
Addison's disease

Question 6

What causes acidosis with a raised anion gap?

Answer 6

lactate: shock, sepsis, hypoxia
ketones: diabetic ketoacidosis, alcohol
urate: renal failure
acid poisoning: salicylates, methanol

Question 7

How do you calculate the anion gap?

Answer 7

Na+ + K+) - (Cl- + HCO-3)

The normal range = 10-18 mmol/L

Question 8

What are the causes of respiratory alkalosis?

Answer 8

anxiety leading to hyperventilation
pulmonary embolism
salicylate poisoning*
CNS disorders: stroke, subarachnoid haemorrhage, encephalitis
altitude
pregnancy