Fluid Balance, Sodium and Potassium Flashcards Preview

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Flashcards in Fluid Balance, Sodium and Potassium Deck (44)
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1

What % of the body is water?

60%

2

what is the ratio of Intracellular fluid to Extracellular fluid?

2:1

3

3 areas where extracellular fluid can be?

Intravascular
Interstitial (bathing cells- the largest component of ECF
Transcellular (within epithelial-lined spaces, e.g. CSF, joint fluid, bladder urine, aqueous humour)

4

What is Osmolality?

Total number of particles in solution - measured with an osmometer., units = mmol/kg

5

What is Osmolarity?

Calculated, measure of solute per liter of solution, units - mmol/l

=2(Na + K) +urea + glucose

6

Physiological and Pathological determinants of osmolality/osmolarity in serum/plasma..

Physiological - Na+K+Cl+HCO3+urea+glucose
Pathological = Endogenous (i.e. glucose), Exogenous (ethanol, mannitol)

7

What can osmolality be used to diagnose?

SIADH - the normal range for serum osmolality is 275-295mmol/kg

8

What is the difference between osmolality and osmolarity known as?

the osmolar gap, and can be useful in metabolic acidosis cases

osmolality and osmolarity should roughly equate

9

Normal ranges for Sodium?

135-145 mmol/l

10

How is Sodium distributed around the body?

70% is freely exchangeable, the rest complexed in bone

11

How are levels of sodium maintained?

Predominantly an extravellular cation, largely maintained by active pumping from ICF>ECF by NA/K ATPase

12

Hyponatraemia - Values at which symptoms occur

less than 136 = Nausea and vomiting
less than 131 = confusion
less than 125 = non cardiogenic pulmonary oedema
less than 117 = coma

13

Hyponatraemia - treatment?

Treat underlying cause not the hyponatreamia (unless severe

14

Hyponatraemia - symptoms?

Symptomatic hyponatraemia is a medical emergency

15

What is TURP syndrome?

Hyponatraemia from water absorbed through damaged prostate

16

In true hyponatraemia is Osmolality high or low?

Low

17

Causes of hypovolaemic hyponatraemia ?

Urinary Sodium greater than 20mmol/l= Renal
- Diuretics, Addison's, Salt losing nephropathies

Urinary Sodium less than 20mmol/l = Non-Renal
- Vomiting, Diarrhoea, excess sweating, Third space losses (ascites, burns)

18

Causes of Euvolaemic hyponatraemia?

Urinary Sodium >20mmol/l - SIADH, Primary polydipsia, Severe hypothyroidism

19

Causes of Hypervolaemic hyponatraemia?

Urinary Sodium >20mmol/l = Renal
- ARF, CRF

Urinary Sodium less than 20mmol/l = Non-Renal
- Cardiac failure, Cirrhosis, Inappropriate IV fluid

20

Correction of Hyponatraemia, things to be aware of?

Rapid correction can lead to Central Pontine Myelinolysis (pseudobulbar palsy, paraparesis, locked-in syndrome) therefore aim to increase Na by 1mmol/l per hour

21

Causes of hyponatreamia post surgery?

Over hydration with hypotonic IV fluids

Transient increase in ADH due to stress of surgery

22

Lab criteria for SIADH

True Hyponatraemia (low serum osmolality)
Clinically euvolaemic
Inappropriately high urine osmolality and increased renal sodium excretion (>20mmol/l) due to decreasing aldosterone levels
Normal renal, adrenal, thryroid and cardiac function

A diangosis of exclusion

23

Causes of SIADH

-Malignancy - small cell lung cancer, pancreas, prostate, lymphome (ectopic secretion)
-CNS disoders - meningoencephalitis, haemorrhage, abscess
-Chest Disease - TB, pneumonia, abscess
-Drugs - opiates, SSRIs, carbamazepine

24

Hypernatraemia - sodium level? symptoms? classification? what ward is it most likely to be seen on?

- Less common than hyponatraemia, but usually clinically significant (plasma NA> 148mmol/l)
-Symptoms = thirst--> confusion --> seizures + ataxia --> coma
- can be classifed based on hydration status
- In hospital often iatrogenic, common problem in ITU patients

RAPID CORRECTION CAN LEAD TO CEREBRAL OEDEMA!!!

25

What causes Hypovolaemic Hypernatraemia?

- GI loss - vomiting, diarrhoea
- Skin loss - excess sweating, burins
- Renal loss - loop diuretics, Renal disease (impaired concentrating ability), Osmotic diuresis (glucose, mannitol)

26

What causes Euvolaemic Hypernatraemia?

- Respiratory loss - Tachypnoea
- Skin loss - excessive sweating, Fever
- Renal loss - Diabetes Insipidus
- Misc - No water!

27

What causes Hypervolaemic Hypernatraemia?

- Mineralocorticoid excess (Conns Syndrome)
- Hypertonic saline

28

Clinical features of Diabetes Insipidus?

- Hypernatraemia (lethargy, thirst, irritability, confusion, coma, fits)
- Clincially euvolaemic
- Polyuria and polydipsia
- Urine: Plasma olsmolality is less than 2

29

What are the 2 types of Diabetes Insipidus?

1) Cranial
2) Nephrogenic

30

What is Cranial Diabetes Insipidus and what are the causes of it?

Lack of/ No ADH
causes
- Head trauma
- Tumour
- Surgery