Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chemical pathology > Sodium Balance > Flashcards

Sodium Balance Flashcards

1
Q

What is the commonest electrolyte abnormality in hospitalised patients?

A
  • LOW Na (HYPOnatraemia/ HypoNa)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

DEFINITION of Hyponatraemia

A

Serum sodium < 135mmol/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

normal range of sodium

A
  • Normal range: 135-145mmol/L
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Pathogenesis of Hyponatraemia

A
  • Increased EXTRACELLULAR water
  • (Get excess water due to increased ADH secretion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does ADH work

A
  • ADH is synthesised in the hypothalamus + released from posterior pituitary
  • It acts on the distal tubules on kidneys to promote WATER RETENTION.
  • It inserts Aquaporin 2 into the membrane to retain water + increase in extracellular water
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

more ADH =

A

MORE WATER REABSORPTION

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

which receptors does ADH work on

A
  • Acts on V2 receptors on collecting duct = insertion of aquaporin 2
  • Acts on V1 receptors on VSMCs >> vasoconstriction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

ADH is stimulated by…. (2)

A

o HIGH serum osmolality: mediated hypothalamic Osmoreceptors

o LOW blood volume/ BP detected by baroreceptors in carotids, atria and aorta

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

• Osmolarity equation

A

2(Na+K) + urea + glucose

normal range: 275-295mOsmol/kg

**basc: cations+anions+ uncharged molecules**

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

increased ADH means

A

increased water retention = increased extracellular water = hyponatraemia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

First Step in Clinical Assessment of a Hyponatraemic Patient

A

assessment of volume status: euvolaemic, hypo- or hypervolaemic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Clinical Signs of Hypovolaemia

A
  • reduced skin turgor
  • prolonged capillary refill
  • dry mucous membranes
  • hypotension (postural)
  • Confusion/ drowsiness
  • Reduced urine output
  • LOW URINE Na+ (< 20)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

MOST RELIABLE clinical sign of hypovolaemia

A

- LOW URINE Na+ (< 20)

**this is in the case of extra-renal losses**

**in renal losses eg if patient is on diurectics- they will have ah igh urine sodium regardless**

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Clinical Signs of Hypervolaemia

A
  • raised JVP
  • ascites
  • pulmonary oedema: bibasal crackles on chest examination
  • peripheral oedema
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

hypovalaemic causes of hyponatraemia

A

renal causes:

  • thiazide diuretics
  • salt losing nephropathy
  • salt wasting syndromes (post-operative)

extra renal causes:

  • vomiting, diarrhoea
  • burns

mechanism

- loss of fluid –> low BP–> detected by baroreceptors–>ADH release–>water reabsorption–>dilution of extracellular fluid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

euovalaemic causes of hyponatraemia (and what is the mechanism?)

A

adrenal insufficiency (addison’s disease)
SIADH
hypothyroidism

mechanism

  • to begin with these patients are euvolaemic- they have no problem with their volume status or blood pressure
  • for some reason (not sure exact) these conditions cause ADH to be released–>water reabsorption–>raises BP
  • body doesn’t like this raised BP–>releases ANP–>natriuresis (loss of sodium + some fluid)–> this then normalises the volume status, but in the process they have lost some sodium
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

hypervolaemic causes of hyponatraemia and what is the mechanism?

A

cardiac failure
nephrotic syndrome /renal failure
cirrhosis

mechanism

  • heart failure: pump failure –> low BP–> ADH release–> water reabsorption
  • cirrhosis: high nitric oxide and other vasodilators (as the liver cannot break them down)–>fall in BP–>ADH release–>water reabsorption
  • renal failure: kidneys aren’t functioning–>reduced water excretion–>more water retention–>hyponatraemia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

is hypovalaemia same as dehydration

A
  • Dehydration is JUST loss of water
  • Hypovolaemia is loss of SALT AND WATER
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

hypovolaemic hyponatraemia: how to distinguish between renal vs non-renal losses ?

A

o Urine Na > 20- renal losses (e.g. diuretics, salt-wasting syndromes)

o Urine Na < 20- non-renal losses (e.g. vomiting, diarrhoea, burns)

**therefore the point about urine sodium <20 being the most reliable indicator of hypovolaemic hyponatramiea is only in the case of extra-renal losses**

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

urinary sodium levels in hypervolaemic causes of hyponatraemia

A
  • Cardiac failure: Urine Na is low
  • Cirrhosis: Urine Na is low
  • *- Renal failure: Urine Na is high (bc it’s not able to reabsorb sodium)**

**Karim’s path book: urine osmolality>20 mmol/L suggests renal cause**

**confirm whether it’s urine sodium or urine osmolality**

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

urinary sodium levels in euvolaemic causes of hyponatraemia

A
  • Hypothyroidism: urine Na is low
  • Adrenal insufficiency: urine Na is high

**- SIADH: high urine sodium**

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Causes of SIADH

A
  • CNS: subdural haematoma, subarachnoid haemorrhage, trauma, cavernous sinus thrombosis
  • lung: lung cancer, pneumoniae, PE, pneumothorax
  • drugs: (SSRI, sodium Valproate, TCAs, PPI, carbamazepine)
  • Tumours
  • Surgery (make excess ADH post-operatively)

**KM book: it’s pneumonia in the context of lung cancer rather than pneumonia itself**

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is pseudohyponatraemia

A

excess protein and lipids leads to apparent hyponatraemia but there is NORMAL OSMOLALITY

seen in myeloma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

biochemical markers for real hyponatraemia

A

o LOW serum osmolality
o HIGH urine osmolality- making excess ADH so retaining water (so concentrated urine)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

biochemical markers for SIADH

A

o LOW plasma osmolality
o HIGH urine osmolality

26
Q

Investigations Ordered in Euvolaemic Hyponatraemia

A

TFTs- hypothyrodism

short Synacthen test- adrenal insufficiency

plasma + urine osmolality (low plasma + high urine) - SIADH

27
Q

Diagnosis of SIADH

A
  • No hypovolaemia
  • No hypothyroidism
  • No adrenal insufficiency
  • REDUCED plasma osmolality
  • INCREASED urine osmolality (>100)

KM book:

1) 2 low in the blood: low sodium and low osmolality
2) 2 high in the urine: urine sodium >20, urine osmolality high
3) 3 exclusions: no renal/adrenal/thyroid/cardiac disease, no hypovolaemia, no contributing drugs!!

**don’t forget the drugs**

28
Q

Management of HYPOvolaemic Hyponatraemia

A
  • 0.9% NaCL volume replacement
29
Q

what is main concern about giving fluids to manage HYPOvolaemic Hyponatraemia

A

if Na raised too rapidly: cerebral pontine myelinolysis

shrinkage of cells = BBB disrupted = inflammatory cells go into brain:

  • quadriplegia
  • dysarthria
  • dysphagia
  • seizures
  • coma + death
30
Q

how quickly should Na be increased in management of hyponatraemia

A

Serum Na must NOT be corrected > 8-10mmol/L per 24 hours

31
Q

should you give NaCl in SIADH

A

Do NOT GIVE NaCl in SIADH:
the hyponatraemia will get worse- fluid overload

can lead to cerebral oedema and death

32
Q

Management of HYPERvolaemic Hyponatraemia

A

fluid restriction and treat underlying cause

**how does this work: essentially when you fluid restrict someone, over time they naturally start to lose water through other sources like sweating and respiration, eventually normalising fluid status and sodium concentration**

33
Q

Management of EUvolaemic Hyponatraemia

A

fluid restriction and treat underlying cause

**Same principle: essentially when you fluid restrict someone, over time they naturally start to lose water through other sources like sweating and respiration, eventually normalising fluid status and sodium concentration**

34
Q

how should you manage severe Hyponatraemia + how does it present

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

if they do not have a reduced GCS and are not fitting, do NOT think about giving this

35
Q

Drugs used to treat SIADH

A

o Demeclocycline: Monitor U&Es as risk of nephrotoxicity

o Tolvaptan: V2 receptor antagonist

36
Q
  • DEFINITION of Hypernatraemia
A

Serum [Na] > 145mmol/L

37
Q

Causes of Hypernatraemia

A
  • Unreplaced water loss:
    o GI losses, sweat losses
    o Renal losses: osmotic diuresis, reduced ADH release/ action (Diabetes Insipidus)
  • Patient cannot control water intake: people who cannot drink water e.g. children/elderly

**NB: GI losses can cause both hypntaramiea or hypernatramiea depending on whether the patient is able to drink to correct the fluid loss**

38
Q

Investigations for suspected DI

A
  • Serum glucose (exclude DM)
  • Serum K+ (exclude hypoK)
  • Serum Ca (exclude hyperCa)
  • Plasma and urine osmolality
  • Water deprivation test

main ones: plasma and urine osmolality + water deprivation test

39
Q

Treating Hypernatraemia

A
  • Fluid replacement with 5% dextrose
  • treat underlying cause
40
Q

how do you treat hypovolaemia AND hypernatremia

A

give normal saline to correct the volume depletion but then to correct the hypernatremia, you also give 5% dextrose.

**and then need to do serial sodium measurements**

41
Q
  • 70 y/o man
  • 3-day history of diarrhoea
  • Altered mental status
  • Dry mucus membranes
  • Serum Na+ is 168mmol/L

what is the management :

A

hypovolaemia AND hypernatremia:

  1. Correct water deficit – 5% dextrose
  2. Correct EC fluid volume depletion – 0.9% saline
  3. Serial Na+ measurements – every 4-6 hours
42
Q

What are the effects of Diabetes mellitus on serum Na?

A

Variable effect on serum Na depending on the degree:

Hyperglycaemia: draws water out of the cells into ECF = hyponatraemia

Osmotic diuresis in uncontrolled diabetes: hypernatraemia due to renal fluid loss

43
Q

biochemical markers for diabetes insipidus

A

HIGH plasma osmolality and LOW urine osmolality

44
Q

Summary of assessment of hyponatraemia

A
45
Q

If a patient is on diuretics, how does that affect volume status assessment?

A

need to stop their diuretics before measuring as this will affect their urine sodium measurement (it would be high)

46
Q

is sodium predominantly an itracellular or extracellular cation?

A

Largely an extracellular cation, maintained by active pumping from ICF–> ECF

ECF fluid is directly dependent on Na_

47
Q

What is the first step when you detect hyponatramiea in a patient?

A

establish whether true hyponatrameia by checking serum osmolality

a) low: true hypontaramiea

b) normal: spurious, drip arm sample, pseudohyponatramiea (hyperlipidaemia/paraproteinaemia)

  • the lab detects the lipids and paraproteins to be part of water so sodium appears diluted and osmolality will be normal

c) high: glucose/mannitor infusion - these osmotically active substances draw water out of cells which dilutes down the sodium

48
Q

flowchart summarising approach to hyponatramiea

A
49
Q

Why could you get hypontaramiea post surgery?

A

1) overhydration with hypotonic IV fluids
2) transient increase in ADH due to the stress of the surgery

50
Q

Clinical features of diabetes insipidus

A

Hypernatraemia (lethargy, thirst, irritability, confusion, coma, fits)
• Clinically euvolaemic
• Polyuria and polydipsia
• Urine: plasma osmolality is <2
(Urine is dilute despite concentrated plasma)

51
Q

Types of diabetes inspidius

A
52
Q

Distinguishing between diff types of diabetees inspidus and primary polydipsia

A

**rmb the osmolality needs to rise to >600*!!!!!

just because it rises slightly does not mean it is cranial DI

53
Q

Osmolality vs osmolarity

A

OsmolaLity is a measure of all the particles in a solution and is measured in mmol/kg.

OsmolaRity is an alternative measure of the particles in solution and has the units mmol/L. OsmolaRity is calculated using the formula below:

Osmolarity = 2(Na + K ) + urea + glucose

You may notice we do not need to know the concentration of negative ions in order to calculate osmolarity. The concentration of negative ions should equal the concentration of positive ions. Therefore we simply multiply the positive ions by 2.

OsmolaLity and OsmolaRity should roughly equal. If they do not this is called the Osmolar gap.

You may ask why we have two different but similar terms. OsmolaRity can be easily calculated from the concentration of electrolytes, however, because it is measured per 1 Litre of solvent it can vary with temperature. OsmolaLity requires measuring in a lab using an osmometer, but does not vary with temperature as it is measured per 1 Kilogram of solvent, and is therefore the preferred term for biological systems.

54
Q

Does osmometer measure osmolality or osmolarity?

A

Osmolality

units: mmol/kg

55
Q

Is the calculated version osmolarlity or osmolality?

A

osmolarity

mmol/L

56
Q

As a generla rule in SIADH how does the urine and plasma osmolality compare?

A

urine osmolality>plasma osmolality

57
Q

primary polydipsia

A

low plasma osmolality

low urine osmolality

58
Q

Which drugs cause SIADH?

A

SSRI, sodium Valproate, TCAs, PPI, carbamazepine

Depression: SSRI, TCAs

AED: sodium valproiate and carbamazapine

Other: PPI

59
Q
A
60
Q

what is cerebral salt wasting syndrome?

A

head injury leads to natriuresis –> sodium and water loss in the kdienys–> depletes intravascular volume–> stimulates release fo ADH to increase water retention

**primary problem is the salt loss from the kidenys rather than ADH secretion; ADH secretion is secondary**

chemical pathology (22 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions