Sodium Fluid Balance

Question 1

Osmolality vs Osmolarity

Answer 1

Osmolality= mosm/kg
Osmolarity= mosm/L

Question 2

What are the characteristics of Osmolality and Osmolarity?

Answer 2

Osmolality- lab calculated, accurate, unchanged by volume change
Osmolarity= more practical, easier to measure Ls of blood than Kgs

Question 3

What is the Osmolarity gap?

Answer 3

The difference between lab calculated Osmolality and my Osmolality calculation

Question 4

What causes an Osmolarity gap?

Answer 4

Additional solutes than Na, K, glucose and urea

Question 5

Osmolality equation

Answer 5

2(Na + K) + glucose + urea

Question 6

What should normal Osmolality be?

Answer 6

275-295 mosm/L

Question 7

What value indicates an similar gap

Answer 7

> 10 mosm/L difference between lab value and my calculation

Question 8

What regulates Na?

Answer 8

Blood volume and Osmolality

Question 9

What happens when blood volume increases?

Answer 9

Atrial stretch, Atrial Natriuretic Peptide released, aldo renin adh decreased

Question 10

What is the moa of aldosterone?

Question 11

What is the Moa of renin?

Question 12

What is the moa of adh?

Question 13

What happens when blood Osmolality is high?

Answer 13

Thirst +Adh release

(Opposite for low Osmolality)

Question 14

Step 1 of assessing hyponatraemia

Answer 14

Check plasma Osmolality

Need to know this is actually hyponatraemia!

Question 15

What can cause euosmolar hyponatraemia

Answer 15

High lipids, proteins
Pseudohyponatraemia

Question 16

What can cause hyperosmolar hyponatraemia

Answer 16

High glucose, ETOH
Pseudohyponatraemia

Question 17

What is step 2 of assessing true hyponatraemia?

Answer 17

Assess volume status

Question 18

How do we assess volume status

Answer 18

BP, HR, CRT
Leg oedema
Pulmonary Oedema

Question 19

What is step 1 of assessing hypovolaemic hyponatraemia?

Answer 19

Check urinary Na

Question 20

What does urinary Na <20mosm/L indicate in hypovolaemic hyponatraemia?

Answer 20

Extra renal loss

Vomiting, diarrhoea, burns,

Question 21

What does urinary Na >20mosm/L indicate in hypovolaemic hyponatraemia?

Answer 21

Renal Na Loss

Renal disease, cerebral salt wasting, diuretics- thiazides

Question 22

What is the underlying mechanism behind hypervolaemic hyponatraemia?

Answer 22

High total body water, but low intravascular volume
Fluid in the wrong place!

Question 23

What is the first step of assessing hypervolaemic hyponatraemia?

Answer 23

Check urine Na

Question 24

What does urinary Na <20mosm/L indicate in hypervolaemix hyponatraemia?

Answer 24

Congestive Cardiac Failure, Cirrhosis, nephrotic syndrome

Question 25

What does urinary Na >20mosm/L indicate in hypervolaemix hyponatraemia?

Answer 25

CKD

Question 26

How do we manage hypovolaemic hyponatraemia?

Answer 26

Treat cause IV 0.9% NaCl

Question 27

How do we manage hypervolaemic hypernatraemia?

Answer 27

Treat cause Fluid restrict

Question 28

What is the mechanism of hypovolaemic hyponatraemia?

Answer 28

Low total body water with appropriately high ADH, hence retaining more water relative to sodium

Question 29

What is the mechanism of euvolaemic hyponatraemia?

Answer 29

Increased water relative to sodium

Question 30

What is the first step in assessing euvolaemic hyponatraemia?

Answer 30

Check urinary sodium

Question 31

What does urinary Na <20mosm/L indicate in euvolaemic hyponatraemia?