Sodium regulation

Question 1

How is ADH release stimulated and what role does it play in sodium homeostasis?

Answer 1

Fluid depletion results in an increase in plasma osmolality which is sensed by osmoreceptors in the hypothalamus. ADH is released from the posterior pituitary which stimulates thirst and renal water reabsorption

Question 2

How is aldosterone release stimulated and what role does it play in sodium homeostasis?

Answer 2

Aldosterone is released when the juxtaglomerular apparatus senses decreased renal artery perfusion. This leads to the release of renin which cleaves angiotensinogen into angiotensin 1. This is converted into angiotensin 2 which then goes to the adrenal cortex and induces aldosterone release. Aldosterone increases sodium reabsorption in the distal convoluted tubule.

Question 3

What is the usual sodium range in the body?

Answer 3

133-146mmol/L

Question 4

What difference is there in terms of cerebral impact in rapid and slow development of hyponatraemia?

Answer 4

In rapid hyponatraemia, water will move intracellularly and lead to cerebral oedema. In slow hyponatraemia, the brain will compensate by losing solutes therefore preventing oedema formation.

Question 5

At what sodium level do patients become symptomatic? What are these symptoms?

Answer 5

Headache

Nausea and vomiting

Muscle cramps

Lethargy

Restlessness

Disorientation

Question 6

At what sodium level do the concerns about severe effects from hyponatraemia become apparent? What are these effects?

Answer 6

<120mmol/L

Risk of seizure, coma, brain damage, brainstem herniation

Question 7

What are the 3 types of hyponatraemia?

Answer 7

Euvolemic

Hypovolemic

Hypervolemic

Question 8

How is serum osmolality calculated? What is a normal range?

Answer 8

2xNa + urea+ glucose

280-295mOsm/kg

Question 9

What is the flowchart of low sodium causes and their treatments?

Answer 9

Question 10

Give 5 categories of causes of SIADH.

Answer 10

1. Tumours- small cell lung cancer
2. Chest disease- Tb, pneumonia
3. CNS disorders- pituitary adenomas, infections, head injury, Guillian-Barre
4. Iatrogenic- Chemo, MAOIs, phenothiazines, carbazapine
5. Metabolic disorders- hypothyroidism, porphyria

Question 11

What are the clinical features of hypernatraemia?

Answer 11

FRIED

• fever and flushed skin
• restless
• increased fluid oedema and bp
• edema peripheral and pitting
• Decreased urine output, dry mouth

Question 12

What are the causes of elevated sodium?

Answer 12

fluid loss

diabetes insipidus

osmotic diuresis

primary hyperaldosterinism

iatrogenesis

Question 13

Examination into hypernatraeia should first assess whether the patient is in fluid excess or deficit. Fluid excess indicates which condition?

Answer 13

Hyperaldosteronism

Question 14

What is the management of hypernatraemia?

Answer 14

rehydrate with water or 5% IV dextrose