Sodium and fluid balance

Question 1

What controls sodium balance?

Answer 1

Water - controlled by ADH
Salt - Aldosterone

Question 2

Where does ADH work?

Answer 2

V1 - vasoconstriction
V2 - aquaporin 2 inserted into collecting duct cells

Question 3

What is the most common sodium abnormality?

Answer 3

Hyponatremia

Question 4

Most common cause of hyponatremia

Answer 4

Fluid overload

Question 5

If someone has hyponatremia, what do you have to assess?

Answer 5

Their fluid status - are they hypovolemic, euvolemic or hypervolemic

Question 6

Clinical features of hypovolemia

Answer 6

Low BP
Tachycardia
Dry skin turgor
Low urine output
Low urine sodium <20

Question 7

What is the best marker of HYPOVOLEMIA?

Answer 7

Low sodium in urine <20

Question 8

Clinical features of hypervolemia

Answer 8

Oedema
Raised JVP
Bibasal crackles

Question 9

Causes of hyponatremia in hypovolemia

Answer 9

If urine sodium less than 20:
Diarrhoea and vomiting
Excess sweating
Ascites/burns

If urine sodium more than 20: (kidney not retaining sodium)
Diuretics
Salt losing nephropathy
Addisons

Question 10

Causes of hyponatremia in euvolemia

Answer 10

SIADH
Addisons/adrenal insufficiency
Hypothyroidism - low heart rate,

Question 11

Causes of hyponatremia in hypervolemia

Answer 11

Urine sodium less than 20
Cardiac failure - low BP, increases ADH secretion
Cirrhosis - Nitric oxide release - vasodilation - low bp - ADH secretion

Urine sodium more than 20
Renal failure/nephrotic syndrome

Question 12

Tests to identify hypovolemic hyponatremia

Answer 12

No tests as such, check if clinically hypovolemic

Question 13

Tests to identify euvolemic hyponatremia cause - list three

Answer 13

TFTs

Short synACTHen test - to test for adrenal insufficiency (cortisol rise)

Plasma and urine osmolality for the SIADH (low plasma osmolality, high urine osmolality as osmolality is calculated from sodium)

Question 14

Tests to identify hypervolemic hyponatremia

Answer 14

No tests as such, visually see if fluid overloaded

Question 15

Causes of SIADH

Answer 15

CNS pathology
Lung pathology
Drugs - SSRIs, TCA, Opiates, PPis, carbamazepine
Tumours
Surgery

Question 16

How would you diagnose SIADH?

Answer 16

Pt must not be:
hypovolemic
no hypothyroidism
no adrenal insufficiency

they do have:
reduced plasma osmolality
increased urine osmolality (over 100)

Question 17

Management of someone with hypovolemic hyponatremia

Answer 17

Volume replacement with 0.9 percent saline - this reduces the stimulus for excess ADH

Question 18

How would you manage hypervolemic hyponatremia?

Answer 18

Fluid restriction
Treat underlying cause

Question 19

How would you manage a euvolemic patient with hyponatremia?

Answer 19

Fluid restriction
Treat underlying cause e.g. thyroxine, gluocorticoids etc

Question 20

What clinical feature is a marker of severe hyponatremia?

Answer 20

If pt has reduced GCS
Seizures

Question 21

Management of SEVERE hyponatremia

Answer 21

CALL ON CALL CONSULTANT
Hypertonic 3 percent saline

Question 22

What is important to remember when correcting hyponatremia?

Answer 22

Serum sodium must not be corrected >8-10mmol / L in the first 24 hours as there is a risk of osmotic dehydration causing central pontine myelinolysis

Question 23

Symptoms of central pontine myelinolysis

Answer 23

Quadriplegia, dysarthria, dysphagia, seizures, coma, death

Question 24

Drugs used to treat SIADH

Answer 24

Demeclocycline

Tolvaptan

Question 25

Demeclocycline mechanism of action + what you must do if prescribing someone this drug

Answer 25

Reduces tubule cells' response to ADH but monitor U and E as risk of nephrotoxicity

Question 26

Tolvaptan mechanism of action

Answer 26

V2 receptor antagnoist

Question 27

Hyponatremia is mostly due to reduced body sodium or increased body water?

Answer 27

Increased extracellular body water

Question 28

What counts as hypernatremia?

Answer 28

Serum sodium over 145mmol/L

Question 29

Causes of hypernatremia

Answer 29

GI loss Sweat loss Renal loss Osmotic diuresis Reduced ADH release/action e.g. in diabetes insipidus

Question 30

Which type of patient often gest hypernatremia?

Answer 30

People who cannot control water intake e.g. children or elderly not drinking enough

Question 31

What investigations would you order in a patient with suspected diabetes inspidus? What tests are done to be excluded? What test is specifically done for diabetes inspidus diagnosis?

Answer 31

So they are peeing a lot because the ADH isn't working, so: Serum glucose to exclude DM Serum potassium to exclude hypokalemia Serum calcium to exclude hypercalcemia Plasma and urine osmolality Water deprivation test

Question 32

How do you treat hypernatremia?

Answer 32

Fluid replacement Treat underlying cause

Question 33

70 yo man with 3 days of diarrhoea, altered mental status and dry mucous membranes. Serum sodium is 168 mmol/L. How do you manage?

Answer 33

Correct lack of water with 5 percent dextrose as this is causing the high sodium. You also need to correct the extracellular fluid volume depletion - 0.9 percent saline He also needs serial sodium measurements every 4-6 hours

Question 34

Do we use sodium chloride to correct hypernatremic lack of fluid?

Answer 34

NO you use 5 percent dextrose instead

Question 35

What are the effects of diabetes mellitus on serum sodium?

Answer 35

Variable: Hyperglycemia can draw water out of the cells, causing hyponatremia (glucose can draw water into the vessels) Osmotic diuresis (peeing it out) can cause loss of water and therefore hypernatremia

Question 36

How do hypercalcemia and hypokalemia cause you to pee out more?

Answer 36

Because it causes resistance to ADH, and therefore diabetes inspiidus

Question 37

Three problems causing you to pee loads

Answer 37

Hypercalcemia Hypokalemia Hyperglycemia

Question 38

How do you test whether it is a true hyponatremia?

Answer 38

Check serum osmolality - osmolarity

Question 39

If the osmolality is high, what does this mean?

Answer 39

There are other solutes in the blood, causing water to come in and dilute the sodium. This is one type of pseudohyponatremia. Causes: mannitol, glucose infusion

Question 40

In true hyponatremia, what should the osmolality be?

Answer 40

It should be low too

Question 41

If the osmolality is normal, what does this mean?

Answer 41

Lipids, paraproteins - these are detected by the lab as being water, so it comes back as normal This is also pseudohyponatremia Other causes: Drip arm sample False sample

Question 42

Name a procedure where you get hyponatremia

Answer 42

TURP - glycine 1.5 percent solution is absorbed from the irrigation, and dilutes the sodium

Question 43

How do you calculate osmolarity?

Answer 43

2 x (Na + K) + urea and + glucose