Electrolyte disturbance

Question 1

How is hyponatraemia defined?

Answer 1

-Normal serum conc = 135-145 mmol/L
-Normal urine conc = <20 mmol/L
-Hyponatraemia represents a relative excess of water in relation to sodium and is defined as serum sodium <135

Question 2

How does hyponatraemia present?

Answer 2

-Often asymptomatic
-Mild = anorexia, headache, nausea, vomiting, lethargy
-Moderate = personality change, muscle cramps / weakness, confusion, ataxia
-Severe = drowsiness

Question 3

How should you investigate hyponatraemia?

Answer 3

-Clinical examination ie fluid status, BP, HR, cap refill
-Serum Na+
-Serum K+ (if raised, ?Addison’s)
-Urine Na+ (if raised, ?renal cause)
-SIADH confirmed by paired serum and urine Na+
-TFTs to exclude hypothyroidism
-Random serum cortisol level if adrenal suppression suspected

Question 4

How is hyponatraemia managed?

Answer 4

-Find underlying cause
-Ascertain whether hypo-, eu- or hypervolaemic?
-Either treat underlying cause or give 0.9% saline

Question 5

What are the risks of treating hyponatraemia?

Answer 5

-Osmotic demyelination syndrome
-Pontine myolysis (locked in syndrome)
–Rapidity of correction of solutes pulls water from cells causing oligodendrocyte damage

Question 6

How is hyperkalaemia defined?

Answer 6

-Plasma K+ >5.5 mmol/L

Question 7

What are the signs and symptoms of hyperkalaemia?

Answer 7

-Non-specific - weakness, fatigue
-Few signs except occasional bradycardia (heart block) or tachypnoea (respiratory muscle weakness)
-Muscle weakness and flaccid paralysis
-Depressed / absent tendon reflexes

Question 8

How would you investigate hyperkalaemia?

Answer 8

-Serum K+ (extracellular conc)
-ECG (intracellular conc)
-24h urine volume and electrolytes
-FBC - normocytic, normochromic anaemia suggests haemolysis
-Capillary BG and plasma glucose
-ABG - metabolic acidosis

Question 9

What will an ECG show in hyperkalaemia?

Answer 9

-Peaked T waves
-Flattened, or loss of P wave
-Wide QRS interval
-Prolonged PR interval

Question 10

How is hyperkalaemia managed?

Answer 10

-30mls 10% calcium gluconate protects heart from arrhythmias (if K+ >6.5 / >6.0 with ECG changes)
-10 units insulin with 50mls dextrose (check BG before, during and after)
-Salbutamol neb 5mg
-Haemodialysis if hyperkalaemia persists