sodium fluid balance

Question 1

What is the commonest electrolyte abnormality in hospitalized patients?

Answer 1

hyponatreamia

Serum sodium < 135 mmol/L

Question 2

What is the underlying pathogenesis of hyponatraemia?

Answer 2

Increased EXTRAcellular water

Question 3

Which hormone controls water balance?

Answer 3

ADH

Question 4

how does ADH (vasopressin) control water?

Answer 4

promotes water retention by inserting

-> aquaporin-2 channels

into the

-> collecting duct cells

Question 5

which receptors does adh act on for fluid balance? and where

Answer 5

V2

collecting duct cells

Question 6

adh binds to V1 receptors ON _____ to promote ___

Answer 6

vascular smooth muscle

vasoconstriction

Question 7

what 2 things increase adh secretion?

Answer 7

1. Increased Serum osmolality (osmoreceptors)
2. Reduced Blood volume/pressure

(baroreceptors in the carotids, atria and aorta)

Question 8

What is the effect of increased ADH secretion on serum sodium?

Answer 8

hyponatraemia

because increased water retention = less sodium as a proportion in blood

Question 9

What is the first step in the clinical assessment of a patient with hyponatraemia?

Answer 9

Clinical assessment of volume status

then

Urinary sodium

Question 10

What are the clinical signs of hypovolaemia?

Answer 10

Low urine Na+ (<20) !

Reduced urine output
Tachycardia
Postural hypotension
Dry mucous membranes
Reduced skin turgor
Confusion/drowsiness

Question 11

what is the MOST RELIABLE clinical sign of hypovolaemia?

Answer 11

Low urine Na+ (<20) !

Question 12

case ; patient on furosemide presents with tachycardia and confusion.

you find they are hypovolaemic.
Urine sodium normal.

what is potentially wrong?

Answer 12

the patient is on diuretics, they will have a high urine sodium regardless of hypovoalemia

Question 13

Clinical Features of HYPERvolaemia?

Answer 13

○ Raised JVP
○ Bibasal crackles
○ Peripheral oedema

Question 14

causes of hypo, hyper and euvolaemia broadly?

Answer 14

Hypovolaemics = things causing fluid loss
Euvoleamics = Endocrine conditions
Hypervolaemia = Organ failures

Question 15

3 organs involved in hypervolaemia?

Answer 15

Heart

Liver

Kidney

Question 16

urine sodium is high in which volume status?

Answer 16

euvolaemia

and hpovolaemia IF on diuretics

Question 17

what osmolality picture characterises SIADH ?

Answer 17

○ Reduced plasma osmolality
○ Increased urine osmolality (> 100)

As a rule of thumb - urine osmolality will be HIGHER than plasma osmolality

because excess fluid retention due to adh secretion

Question 18

What investigations would you order in a patient with euvolaemic hyponatraemia?

Answer 18

Hypothyroidism: Thyroid function tests

Adrenal insufficiency: Short Synacthen test

SIADH: Plasma & urine osmolality

Question 19

How would you manage a hypovolaemic patient with hyponatraemia?

Answer 19

Volume replacement with 0.9% saline

Question 20

How would you manage a euolaemic and

hypervolaemic patient with hyponatraemia?

Answer 20

Fluid restriction

Treat the underlying cause

Question 21

signs of a Severe Hyponatraemia?

treatment?

Answer 21

• Reduced GCS
  
  • Seizures
  • Seek expert help (treat with 3% hypertonic saline)

Question 22

how to correct serum sodium?

what happens if corrected too fast?

Answer 22

Serum sodium must NOT be corrected faster than 8-10 mmol/L in the first 24 hours

it can result in osmotic demyelination (central pontine myelinolysis);

driplegia, dysarthria, dysphagia, seizures, coma and death

Question 23

how to treat SIADH if fluid restriction not enough?

Answer 23

• Demeclocycline
○ Reduces responsiveness of collecting tubule cells to ADH
○ (risk of nephrotoxicity)
• Tolvaptan
○ V2 receptor antagonist
associated with rapid rises in serum sodium

Question 24

define high blood sodium?

cause?

Answer 24

Defined as serum sodium concentration > 145 mmol/L

• Caused by unreplaced water loss i.e sweating etc

Question 25

what is diabetes insidious?

Answer 25

Diabetes insipidus (DI) is a condition characterized by large amounts of dilute urine and increased thirst

Question 26

Investigations for Diabetes Insipidus?

Answer 26

○ Serum glucose (exclude diabetes mellitus)
○ Serum potassium (exclude hypokalaemia)

		§ NOTE: hypokalaemia can induce a nephrogenic diabetes insipidus 

	○ Serum calcium (exclude hypercalcaemia)
	○ Plasma and urine osmolality
	○ Water deprivation test

Question 27

result of water deprivation test for Diabetes insipidus?

Answer 27

would still make lots of dilute urine.

give desmopressin and in central DI, osmolality returns to normal - concentrated.

Question 28

what’s are the 3 steps in treating hypernatraemia?

Answer 28

Correct water deficit
5% dextrose

Correct extracellular fluid volume depletion
0.9% saline

Serial Na+ measurements
Every 4-6 hours

Question 29

does diabetes cause hyper or hyponatraemia?

Answer 29

BOTH

Hyperglycaemia -> hyponatraemia

Osmotic diuresis in uncontrolled diabetes leads to loss of water and hypernatraemia

Question 30

what are the Criteria to diagnose SIADH include the following (meeran book)?

Answer 30

• Hyponatraemia <135 mmol/L

• Plasma osmolality <270 mmol/L
• Urine osmolality >100 mmol/L
• High urine sodium >20 mmol/L
• Euvolaemia
• No adrenal, renal or thyroid dysfunction

Question 31

purpose of urinary sodium in hyponatraemia analysis?

Answer 31

> 20 = Renal cause of hyponatraemia

< 20 = Non-renal

Question 32

https://us02web.zoom.us/postattendee?id=7

Answer 32

Yes