Hyponatremia and Hypernatremia (chemical pathology)

Question 1

What is the normal range of sodium ECF concentration?

Answer 1

135-145 mmol/L

Question 2

What are the symptoms of hyponatremia?(4)

Answer 2

Weakness, dizziness, confusion and coma.

Question 3

What are the signs of hyponatremia? (6)

Answer 3

• Oliguria, tachycardia, weight loss, peripheral circulatory failure, hypotension, decreased skin turgor.

Question 4

Symptoms of acute hyponatremia.

Answer 4

Severe cerebral oedema, coma, seizures and respiratory distress.

Question 5

True or false:
Chronic hyponatremia is a medical emergency.

Answer 5

False, it is acute hyponatremia that is a medical emergency.

Question 6

What are the symptoms of chronic hyponatremia (5)

Answer 6

Headache, restlessness, muscle cramps, vomiting, lethargy.

Question 7

What are the three causes of hyponatremia and their examples?

Answer 7

Decreased ECF volume-Thiazide diuretics, addison’s disease.
Increased ECF volume- Cirrhosis, impaired renal water excretion, heart failure.
Normal ECF volume- SIADH, hypothyroidism, Excessive water intake, psychogenic polydipsia.

Question 8

Three circumstances in which hyponatremia can occur

Answer 8

• Sodium depletion (Hypovolemic hyponatremia)
  -Water excess, sodium normal (euvolemic hyponatremia)
  -Both water and sodium excess- Hypervolemic hyponatremia

Question 9

How do we calculate osmolal GAP

Answer 9

Osmolal GAP = Osmolality - Osmolarity

Question 10

Three things a clinician should do when assessing a patient with hypoNa

Answer 10

• History- time frame to development of hyponatremia.
  -Establish fluid status (water retention/fluid loss)
• Establish true hyponatremia

Question 11

What is true hyponatremia?

Answer 11

Hypotonic hyponatremia

Question 12

What causes isotonic hyponatremia? (2)

Answer 12

• Hyperlipidemia
  Hyperproteinemia

Question 13

What causes hypertonic hyponatremia? (2)

Answer 13

Hyperglycemia
Mannitol

Question 14

What’s the next step to take in case of a hypotonic hyponatremia?

Answer 14

Assess volume status

Question 15

What can be the causes of hypovolaemic hypotonic hyponatraemia ? (7)

Answer 15

Renal losses (urine sodium is high >40)
-Addison’s disease
-Diuretics
-Osmotic diuretics
Ketonuria

Extra-renal losses
-Diarrhoea
-Burns
-3rd space losses

Question 16

What causes euvolaemic hypotonic hyponatraemia? (4)

Answer 16

-Psychogenic polydipsia
-SIADH
-Hypothyroidism
-Secondary adrenal insufficiency

Question 17

What causes hypervolaemic hypotonic hyponatraemia? (5)

Answer 17

Urine sodium levels are high
-Renal failure
Low urine sodium levels
-Nephrotic syndrome
-Liver cirrhosis
Hypoalbuminaemia
-CCF

Question 18

What are the symptoms of hypernatremia? (6)

Answer 18

Thirst, nausea and vomiting, diarrhoea, muscle twitching, confusion.

Question 19

What are the signs of hypernatremia?

Answer 19

Irritability, hypovolemia, decreased skin turgor, dehydration.

Question 20

What causes persistent hypernatremia?

Answer 20

Defect in thirst mechanism.

Question 21

What is the first step in assessing hypernatremia?

Answer 21

Assess volume status

Question 22

What can cause hypovolaemic hypernatraemia?

Answer 22

Renal losses(urine sodium is high)
-Osmotic diuretics
-ATN polyuric phase

Extra-renal losses (urine sodium is low)
-Diarrhoea
-Burns
-Sweating

Question 23

What can cause euvolemic hypernatremia?

Answer 23

Renal losses (urine osmolality is low)
-Diabetes insipidus

Extra-renal losses (urine osmol is high)
-Insensible losses

Question 24

What causes hypervolaemic hypernatraemia? (4)

Answer 24

-Ingestion of sea water
- Overconcentrated formula milk
- Hypertonic saline IV of NaHCO3
- Hypertonic dialysis

Question 25

How does the brain adapt to:
A. Hypernatraemia
B. Hyponatraemia

Answer 25

A. Accumulating intracellular idiogenic molecules.
B. Secreting idiogenic molecules out of brain cells to ECF.

Question 26

What are the effects of hyponatraemia on the brain? (5)

Answer 26

-Low sodium levels on the ECF causes water to move into the brain, which can cause cerebral oedema.
- Adaptation (1) rapid loss of water and salts, tonicity remain low.
- Adaptation (2) slow loss of osmolytes and water to eliminate the oedema.

Note: Rapid correction can lead to brain shrinkage.

Question 27

Effect of hypernatremia on brain (5)

Answer 27

• Extracellular hypertonicity causes water to move out of the brain.
• This causes cerebral shrinkage.
• Adaptation (1) rapid gain of water and salts from ECF, tonicity remains high.
• Adaptation (2) slow gain of osmolytes and water to correct the shrinkage.

Note: Rapid correction may lead to cerebral oedema.