Electolytes

Question 1

Anion gap

Answer 1

(Sodium+potassium)-(chloride+bicarbonate)

Normal range 10-18

Question 2

Metabolic acidosis - normal anion gap

Answer 2

renal tubular acidosis,
GI bicarbonate loss(diarrhoea, fistula, ureterosignoidostomy), drugs,
ammonium chloride injection,
Addison’s disease

Question 3

Metabolic acidosis -raised anion gap

Answer 3

Lactate 
- type A: shock, hypoxia, burns 
- type B: metformin
Ketones - DKA, alcohol
Urate- renal failure 
Acid poisoning - salicylates, methanol

Question 4

Metabolic alkalosis causes

Answer 4

Loss of hydrogen or gain of bicarbonate (Kidney/ GI tract)

• vomiting/ aspiration
• diuretics
• liquorice, carbenlxolone
• hypokalemia
• primary alderosteronism
• congential adrenal hyperplasia
• cushing’s syndrome
• bartter’s syndrome

Question 5

Metabolic alkalosis mechanism

Answer 5

Activation of renin-angiotensin II- aldosterone system
Causes reabsorption of sodium in exchange for H+ in distal convoluted tubule

ECF depletion (vomiting, diuretics) -> na and cl loss -> activation RAA system -> Raised aldosterone levees

In hypokalemia, K shift into cells -> ECF. Shift of H into cells to maintain neutrality

Question 6

Hyponatraemia

Answer 6

Due to water excess or sodium depletion
Psuedo hyponatriemia - hyperlipidemia or drip arm sample
Every 100mg/dL increase of blood glucose will lower Na 1.6meq

Question 7

Hypertonic hyponatriemia

Answer 7

Plasma osmolality >290
Hyperglycaemia
Hypertonic mannitol

Question 8

Isotonic hyponatriemia

Answer 8

Plasma osmolality 275-290
Pseudo hyponatriemia 
Sodium free irrigate solutes
- hysterectomy
- TURP

Question 9

Hypotonic hyponatriemia (hypervolaemic)

Answer 9

Plasma osmolality <275
High ECF
Interstitial fluid shift
-congestive HF
- cirrhosis
- nephrotic syndrome
- renal failure
- sepsis
- anaphylaxis 
- pregnancy

Question 10

Hypotonic hyponatriemia (euvolaemic)

Answer 10

SIADH

• CNS disorders: haemorrhage, surgery, trauma, mass lesions, stroke
• pulmonary: infection, acute resp failure, positive pressure ventilation
• drugs

Hypothyroidism 
Malignancy
Primary poly dips is
Decreased Na intake (tea and toast, beer potomania)
Secondary adrenal insufficiency

Question 11

Hypotonic hyponatriemia (hypovolaemic)

Answer 11

• Cerebral salt wasting: haemorrhage, surgery, trauma
• Hypokalemia
• Renal sodium loss: diuretics, osmotic diuretics, primary adrenal insufficiency, salt wasting nephropathy, bicarbonaturia, ketonuria
• Extra renal sodium loss: diarrhoea, vomiting, blood loss, excess sweating, fluid sequestration (bowel obstruction, peritonitis, pancreatitis, muscle trauma, burns)

Question 12

Hypernatremia

Answer 12

Dehydration
Osmotic diuretics Eg Hyperosmolar non ketotic diabetic coma
Diabetes insipidus
Excess IV saline

Question 13

Potassium regulation

Answer 13

Aldosterone
Acid base balance
Insulin levels

Question 14

Hyperkalaemia ECG changes

Answer 14

Tall tented t waves
Small p waves
Widened QRS
Sinusoidal pattern and asystole

Question 15

Hyperkalemia

Answer 15

Metabolic acidosis (hydrogen and potassium compete for exchange with sodium across cell membrane in distal tubule)

Acute renal failure
Drugs: K sparing diuretic, ace-I, cyclosporin
Addisons
Rhabdomyolosis
Massive blood transfusion

Nb - beta blockers interfere with K transport into cells, potential cause in renal failure

Question 16

Management hyperkalemia

Answer 16

IV calcium gluconate (stabilise cardiac membrane)
Insulin/dextrose, salbutamol men’s (shift extra cellular to intracellular)

Calcium resinous, loop diuretic, dialysis (remove potassium from body)

Question 17

Hypokalemia with alkalosis

Answer 17

Vomiting
Diuretics
Cushing’s syndrome
conn’s syndrome (primary hyperaldosteronism)

Question 18

Hypokalemia with acidosis

Answer 18

Diarrhoea
Renal tubular acidosis
Partially treated DKA
Acetazolamide

Question 19

ECG features hypokalemia

Answer 19

U waves
Small or absent T waves 
Prolong PR interval
ST depression 
LoNg QT

Question 20

Hypomagnesemia causes

Answer 20

Diuretics
TPN
Diarrhoea
Alcohol
Low K/Ca
Cisplatin (NSCLC)

Question 21

Hypomagnesemia features

Answer 21

Paraesthesja
Tetany
Seizures
Arrhythmia
Low PTH secretion -> low calcium
ECG features similar to hypokalemia 
Exacerbates digoxin toxicity

Question 22

Hypophosphatemia causes

Answer 22

Alcohol excess
Acute liver failure
DKA
Refeeding syndrome 
Osteomalacia
Primary hyperparathyroidism

Question 23

Hypophosphatemia consequences

Answer 23

Red cell hemolysis
White cell and platelet dysfunction
Muscle weakness and rhabdo
CNS dysfunction

Question 24

Hypocalcemia ecg

Answer 24

Prolonged QT

Question 25

Trousseau’s sign

Answer 25

Hypocalcemia
Carpal spasm in brachial artery occluded
95% of people with low Ca
1% normal

Question 26

Chvostek’s sign

Answer 26

Hypocalcemia
Less sensitive than Trousseau’s - 70%
10% normal Ca
Tapping over parotid causes facial muscles to twitch

Question 27

Treat severe hypocalcemia

Answer 27

IV calcium gluconate 10ml of 10% solution over 10mins

ECG monitoring

Question 28

Hypercalcemi

Answer 28

Most common malignancy (bone nets, myeloma, PTHrP from squamous lung)
Primary hyperparathyroidism

Question 29

Differentiating MGUS and myeloma

Answer 29

Absence of complications -

Immune paresis, hypercalcemia and bone pain

Question 30

Treatment hypercalcemia

Answer 30

Fluids
Bisohosphonates if malignancy, take 2-3days to work with maximal effect at 7days
Corticosteroids in sarcoidosis