Biochemistry

Question 1

Causes of hyperkalaemia

Answer 1

acute kidney injury
drugs: potassium sparing diuretics, ACE inhibitors, angiotensin 2 receptor blockers, spironolactone, ciclosporin, heparin/LMWH, beta-blockers
metabolic acidosis
Addison's disease
rhabdomyolysis
massive blood transfusion

Question 2

Hyperkalaemia management

Answer 2

1. Stop precipitating factors
2. IV Calcium Gluconate (protect myocardium)
3. Combined insulin/dextrose infusion or Nebulised Salbutamol (Move potassium into cells - short-term)
4. Calcium Resonium Enemas
5. Loop diuretics
6. Dialysis

Question 3

Hyperkalaemia on ECG

Answer 3

Peaked or 'tall-tented' T waves (occurs first)
Loss of P waves
Broad QRS complexes
Sinusoidal wave pattern
Ventricular fibrillation

Question 4

Causes of Metabolic Acidosis with normal anion gap ( = hyperchloraemic metabolic acidosis)

Answer 4

gastrointestinal bicarbonate loss: diarrhoea, ureterosigmoidostomy, fistula
renal tubular acidosis
drugs: e.g. acetazolamide
ammonium chloride injection
Addison’s disease (aldosterone causes reabsorption of Na+ in exchange for H+ in the distal convoluted tubule)

Question 5

Causes of Metabolic Acidosis with raised anion gap

Answer 5

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

Question 6

Causes of Metabolic Alkalosis

Answer 6

vomiting / aspiration (e.g. peptic ulcer leading to pyloric stenos, nasogastric suction)
diuretics - loops cause hypochloraemic alkalosis
liquorice, carbenoxolone
hypokalaemia (kidneys try reabsorb K+ in place of H+)
Conn’s - primary hyperaldosteronism (aldosterone causes reabsorption of Na+ in exchange for H+ in the distal convoluted tubule)
Cushing’s syndrome
Bartter’s syndrome

Question 7

Features of hypokalaemia

Answer 7

muscle weakness, hypotonia

hypokalaemia predisposes patients to digoxin toxicity - care should be taken if patients are also on diuretics

Question 8

Hypokalaemia with alkalosis

Answer 8

vomiting
thiazide and loop diuretics
Cushing’s syndrome
Conn’s syndrome (primary hyperaldosteronism)

Question 9

Hypokalaemia with acidosis

Answer 9

DRAP

diarrhoea
renal tubular acidosis
acetazolamide
partially treated diabetic ketoacidosis

Question 10

ECG: hypokalaemia

Answer 10

U waves
small or absent T waves (occasionally inversion)
prolong PR interval
ST depression
long QT

Question 11

What metabolic disturbance is seen in PE?

Answer 11

Respiratory alkalosis due to hyperventilation