Electrolytes

Question 1

How are sodium levels controlled?

Answer 1

Aldosterone acting on DCT and CD => increased reabsorption of Na via Na/K ATPase

Natriuretic peptides inhibit reabsorption of Na

Question 2

How does a person with hyponatraemia present?

Answer 2

Anorexia, nausea, malaise

Headache, irritability, confusion, seizures

Question 3

What investigations are done in hyponatraemia?

Answer 3

Serum sodium
Serum osmolality
Urine sodium 
Urine osmolality 
TFTs, 9am cortisol/synacthen test

Question 4

What are some causes of hyponatraemia?

Answer 4

Water overload

GI loss, CCF, cirrhosis

SIADH, ACTH/glucocorticoid deficiency

Addison’s

Question 5

How is hyponatraemia managed?

Answer 5

Asymptomatic - fluid restriction, treat underlying cause

Acute/symptomatic/dehydrated - Rehydrate with 0.9% NaCl

Question 6

What can happen with rapid rehydration with hyponatraemia?

Answer 6

Central pontine myelinolysis

Question 7

What is SIADH?

Answer 7

Excess release of ADH
Results in concentrated urine sodium, with hyponatraemia
No hypovolaemia, diuretic use or oedema

Question 8

What are some causes of SIADH?

Answer 8

Malignancy - small cell lung cancer
CNS disorders - stroke, head injury
Drugs - SSRIs, opiates

Question 9

How is SIADH managed?

Answer 9

Treat underlying cause
Fluid restriction
ADH receptor antagonists (vaptans)

Question 10

How does a person with hypernatraemia present?

Answer 10

Lethargy, thirst, irritability

Signs of dehydration - reduced skin turgor, tachycardia, low BP, dry mucous membranes

Question 11

What are some causes of hypernatraemia?

Answer 11

Dehydration - inadequate intake, diabetes insipidus, thirst impairment
Fluid loss - burns, vomiting, diarrhoea, diuretics
Sodium gain - IV fluids, Primary hyperaldosteronism

Question 12

How is hypernatraemia managed?

Answer 12

Treat underlying condition, correct dehydration

IV 5% glucose
0.9% NaCl if hypovolaemic

Question 13

What are complications of hypernatraemia?

Answer 13

Subarachnoid haemorrhage - shrinkage of brian

Quick correction can lead to cerebral oedema

Question 14

What is diabetes insipidus?

Answer 14

Passing large volumes of dilute urine due to impaired water reabsorption
Renal - kidneys don’t respond to ADH
Cranial - reduced ADH secretion posterior pituitary

Question 15

What are some cranial causes of diabetes insipidus?

Answer 15

Idiopathic
Genetic
Trauma

Question 16

What are some nephrogenic causes of diabetes insipidus?

Answer 16

Inherited
CKD
Electrolyte imbalance

Question 17

What investigations are done for diabetes insipidus?

Answer 17

Urine output >3L/day
U&E - hypernatraemia
Blood glucose - exclude DM

High serum osmolality
Low urine osmolality

Water deprivation test

Question 18

How is diabetes insipidus managed?

Answer 18

Treat underlying cause

Cranial - head MRI, check pituitary function
Desmopressin - ADH analogue

Nephrogenic - bendroflumethiazide, reduce salt intake, NSAIDs

Question 19

How are potassium levels controlled?

Answer 19

Mainly intracellular
Uptake into cells stimulated by insulin and catecholamines - via Na/K ATPase

Cation shift - fluctuation with H+

Question 20

How does a person with hypokalaemia present?

Answer 20

Mild - asymptomatic
Muscle weakness, tetany, hypotonia
Palpitations

Question 21

What ECG changes are seen in hypokalaemia?

Answer 21

Small/inverted T waves
U waves
Prolonged PR interval
Depressed ST interval

Question 22

What are some causes of hypokalaemia?

Answer 22

Loss of K - Thiazide/loop diuretics, vomiting, diarrhoea, hyperaldosteronism

Transcellular shift - alkalosis, insulin

Inadequate intake

Question 23

How is mild hypokalaemia (>2.5) managed?

Answer 23

Do ECG, repeat bloods

Oral K supplements

Question 24

How is severe hypokalaemia (>2.5) managed?

Answer 24

ECG, bloods

IV potassium

Question 25

What are complications of hypokalaemia?

Answer 25

Arrhythmias Muscle weakness Contributes to digoxin toxicity

Question 26

How does a person with hyperkalaemia present?

Answer 26

Weakness, fatigue Palpitations Chest pain Bradycardia

Question 27

What are some causes of hyperkalaemia?

Answer 27

Renal - AKI, CKD, mineralocorticoid deficiency, drugs eg spironolactone, ACE inhibitors, ARB Tissue damage => release of K, eg rhabdomyolysis, trauma, burns Acidosis Drugs - digoxin, beta blockers

Question 28

What ECG changes are seen in hyperkalaemia?

Answer 28

Wide QRS Tall T waves Small P waves Sinusoidal pattern

Question 29

What is the management of hyperkalaemia?

Answer 29

ECG, check K levels again with ABG Stabilise heart - calcium gluconate Shift K into cells - insulin and dextrose, nebulised salbutamol Removal of K - calcium resonium, haemodialysis

Question 30

What is the overall effect of parathyroid hormone?

Answer 30

Increase Calcium | Decrease phosphate

Question 31

What are specific actions of PTH?

Answer 31

Increase osteoclast activity Increase reabsorption of calcium at kidney Decrease reabsorption of phosphate in kidney Increase hydroxylation of calcidiol => calcitriol (vitamin D) in kidney

Question 32

What is the overall effect of vitamin D/calcitriol?

Answer 32

Increase Calcium | Increase phosphate

Question 33

What are specific actions of vit D/calcitriol?

Answer 33

Increase absorption of Ca and PO4 from gut Increased reabsorption of Ca and PO4 from kidney Inhibition of PTH release Increase bone turnover

Question 34

How does hypercalcaemia present?

Answer 34

Moans - depression, lethargy Bones - pain Stones - renal colic Groans - abdo pain, constipation, vomiting Inc threshold for AP => reduced neuronal activity

Question 35

What are causes of hypercalcaemia?

Answer 35

Malignancy Primary hyperparathyroidism - adenoma Sarcoidosis Secondary/tertiary hyperparathyroidism - CKD

Question 36

What investigations are required in hypercalcaemia?

Answer 36

FBC, 24hr Ca urine collection, CXR, isotope bone scan | PTH levels

Question 37

How is malignancy identified as a cause of hypercalcaemia?

Answer 37

Low PTH levels - release of PTHrP | CT CAP

Question 38

How is acute hypercalcaemia managed?

Answer 38

If Ca >3.5 and symptomatic: Correct dehydration with 0.9% saline IV bisphosphonates => inhibition of osteoclast Treat underlying cause eg chemo in malignancy, steroids in sarcoidosis

Question 39

How does hypocalcaemia present?

Answer 39

``` Peri-oral paraesthesia Cramps Chvostek's sign Carpopedal spasm Laryngospasm ``` Dec threshold for AP => inc neuronal activity

Question 40

What are causes of hypocalcaemia?

Answer 40

CKD, hypoparathyroidism (post-thyroidectomy) Vit D deficiency, osteomalacia Respiratory alkalosis - panic attack => hyperventilation => low co2

Question 41

How is hypocalcaemia managed?

Answer 41

Mild - PO supplements | Severe - IV calcium gluconate