Electrolyte Disorders

Question 1

Hyponatraemia (<135mmol/L) can be caused by:

Answer 1

Hypervolaemia (due to excess water) - HF, LF, RF, Hypoalbuminaemia

Normovolaemia - Hypothyroid, SIADH, Addison’s

Hypovolaemia (due to salt loss) -

Renal losses - Hyperglycaemia, Diuretics, Adrenal insufficiency

Extra-Renal - D+V, burns, pancreatitis, haemorrhage

Question 2

ADH is activated when the body is thirsty via osmoreceptors in the hypothalamus. It’s function is to:

Answer 2

Increase water reabsorption from the renal collecting ducts. Released by the Posterior Pituitary.

Question 3

How do you differentiate between Na+ renal loss and Na+ extra-renal loss?

Answer 3

Measure urinary sodium - Renal loss > 20mmol/L

Question 4

Hypervolaemic hyponatraemia is most commonly caused by:

Answer 4

Excessive infusion of 5% Glucose (iatrogenic)

Question 5

Symptoms of hypervolaemic hyponatrameia:

Answer 5

Cerebral Oedema - headache, convulsions, coma

Question 6

What is central pontine myelinolysis?

Answer 6

Over-rapid correction of sodium concentration, resulting in quadriparesis, respiratory arrest, seizures due to demyelination most commonly in the pons, but can also occur in basal ganglia, internal capsule, cortex. Diagnosed via MRI.

Question 7

What are Tolvaptan / Conivaptan?

Answer 7

Vasopressin V2 receptor antagonists, work on the collecting duct

Question 8

What are the most common causes of hypernatraemia ?

Answer 8

Reduced water intake

Water loss in excess of Sodium

Question 9

What are the features of hypernatraemia?

Answer 9

Non-Specific - nausea, vomitting, fever, confusion

Question 10

How do you treat hypernatraemia?

Answer 10

Give water or IV dextrose 5% to try and correct levels over 48h

Question 11

How do you treat low potassium? (<3.5mmol/L)

Answer 11

KCL supplements / slow infusion if DKA/ Do ECG monitoring

Question 12

What causes increased redistribution of K+ into cells, causing hypokalaemia?

Answer 12

Increased activity of Na/K/ATPase channel

Alkalosis, B-Agonists or Insulin

Question 13

What is the function of Aldosterone?

Answer 13

Na+ and K+ regulation, a raised K+ results in Aldosterone activation, resulting in increased secretion of K+ via the distal tubules and collecting ducts

Question 14

What are the causes of Hyperkalaemia (>5.0 mmol/L)

Answer 14

Reduced excretion - AKI, ACE-is, NSAISs, K+ sparing diuretics, Addisons, Type 4 RTA

Redistribution - DKA, metabolic acidosis, tissue necrosis, digoxin toxicity, suxamethonium

Increased input - KCL, salt substitutes, blood transfusion

Question 15

What causes hypokalaemia?

Answer 15

Increased renal excretion (>20mmol/L) - Diuretics, corticosteroids, raised aldosterone (LF, HF, Nephrotic syndrome, Cushing’s, Conn’s)

GI losses - vomitting, diarrhoea, ileostomies

Redistribution - Alkalosis, insulin, B-agonists

Reduced intake - Diet, IV fluids inadequate

Question 16

What are the features of hyperkalaemia?

Answer 16

muscle weakness and paralysis due to impaired neuromuscular transmission

Kussmaul’s breathing - low, deep, sighing inspiration and expiration

ECG changes (indicates emergency) - reduced p wave, widened QRS, tented T wave

Question 17

How do you treat hyperkalaemia?

Answer 17

Protect the heart - if > 6.5 or ECG changes:
10ml of 10% Calcium Gluconate bolus
Give again in 5mins if ECG changes persist

Redistribute the K+:
Soluble Insulin 10 units in 50ml of 50% dextrose IV over 30mins
Salbutamol nebuliser
Sodium Bicarbonate if severely acidotic (pH < 6.9)

Reduce K+:
Give Resin, it binds to K+
Try dialysis if everything fails

Monitor Glucose (hourly for 6h after insulin infusion) and K+ (2-4h)

Question 18

What are the features of low magnesium

Answer 18

Similar to hypocalcaemia and hypokalaemia because:
Reduces PTH secretion and leads to PTH resistance
Increases renal excretion of K+

Question 19

How do you treat low magnesium?

Answer 19

If severe, give MgCl infusion

If less severe, give MgO supplement tablets

Question 20

What does anion gap indicate?

Answer 20

Acidosis with normal anion gap (6-12mmol/L) means HCL is being retained or Sodium Bicarbonate is being lost

Acidosis with increased gap (>12mmol/L) means the acidosis is due to an exogenous acid - sakicylates, lactate

Question 21

What are the causes of metabolic acidosis with NORMAL anion gap?

Answer 21

Increased GI loss of HCO - diarhhoea, ileostomy

Increased renal loss of HCO - hyperPTHism, RTA-2, acetazolamide ingestion

Reduced renal H+ loss - RTA-1 and 4

Increased HCl production - increased arginine and lysine catabolism

Question 22

What are the causes of metabolic acidosis with a RAISED anion gap?

Answer 22

Renal failure (sulphate and phosphate acids)

Ketoacidosis - DKA, starvation, alcohol poisoning

Lactic Acidosis - Shock, LF, severe hypoxia, strenuous exercise

Drug poisoning - salycylates

Question 23

What type of acidosis does Renal tubular acidosis cause?

Answer 23

Metabolic acidosis with a normal anion gap