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Path - Chem Path > Fluid Balance, Sodium and Potassium > Flashcards

Fluid Balance, Sodium and Potassium Flashcards

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1
Q

What % of the body is water?

A

60%

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2
Q

what is the ratio of Intracellular fluid to Extracellular fluid?

A

2:1

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3
Q

3 areas where extracellular fluid can be?

A

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

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4
Q

What is Osmolality?

A

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

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5
Q

What is Osmolarity?

A

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

=2(Na + K) +urea + glucose

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6
Q

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

A

Physiological - Na+K+Cl+HCO3+urea+glucose

Pathological = Endogenous (i.e. glucose), Exogenous (ethanol, mannitol)

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7
Q

What can osmolality be used to diagnose?

A

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

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8
Q

What is the difference between osmolality and osmolarity known as?

A

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

osmolality and osmolarity should roughly equate

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9
Q

Normal ranges for Sodium?

A

135-145 mmol/l

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10
Q

How is Sodium distributed around the body?

A

70% is freely exchangeable, the rest complexed in bone

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11
Q

How are levels of sodium maintained?

A

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

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12
Q

Hyponatraemia - Values at which symptoms occur

A

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

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13
Q

Hyponatraemia - treatment?

A

Treat underlying cause not the hyponatreamia (unless severe

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14
Q

Hyponatraemia - symptoms?

A

Symptomatic hyponatraemia is a medical emergency

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15
Q

What is TURP syndrome?

A

Hyponatraemia from water absorbed through damaged prostate

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16
Q

In true hyponatraemia is Osmolality high or low?

A

Low

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17
Q

Causes of hypovolaemic hyponatraemia ?

A

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)

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18
Q

Causes of Euvolaemic hyponatraemia?

A

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

19
Q

Causes of Hypervolaemic hyponatraemia?

A

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

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

20
Q

Correction of Hyponatraemia, things to be aware of?

A

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
Q

Causes of hyponatreamia post surgery?

A

Over hydration with hypotonic IV fluids

Transient increase in ADH due to stress of surgery

22
Q

Lab criteria for SIADH

A 
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
Q

Causes of SIADH

A
  • 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
Q

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

A
  • 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
Q

What causes Hypovolaemic Hypernatraemia?

A
  • GI loss - vomiting, diarrhoea
  • Skin loss - excess sweating, burins
  • Renal loss - loop diuretics, Renal disease (impaired concentrating ability), Osmotic diuresis (glucose, mannitol)
26
Q

What causes Euvolaemic Hypernatraemia?

A
  • Respiratory loss - Tachypnoea
  • Skin loss - excessive sweating, Fever
  • Renal loss - Diabetes Insipidus
  • Misc - No water!
27
Q

What causes Hypervolaemic Hypernatraemia?

A
  • Mineralocorticoid excess (Conns Syndrome)

- Hypertonic saline

28
Q

Clinical features of Diabetes Insipidus?

A
  • Hypernatraemia (lethargy, thirst, irritability, confusion, coma, fits)
  • Clincially euvolaemic
  • Polyuria and polydipsia
  • Urine: Plasma olsmolality is less than 2
29
Q

What are the 2 types of Diabetes Insipidus?

A

1) Cranial

2) Nephrogenic

30
Q

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

A 
Lack of/ No ADH
causes 
   - Head trauma
   - Tumour
   - Surgery
31
Q

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

A 
Receptor defect - insensitivity to ADH
causes 
   - Inherited
   - Lithium
   - Chronic renal failure
32
Q

What test if used to diagnose Diabetes Insipidus?

A

8hr fluid deprication test

33
Q

What is a normal result of a 8hr fluid deprication test?

A

Urine concentration greater than 600mOsmol/kg

34
Q

What result of a 8hr fluid deprication test would lead you to diagnose Primary Polydipsia?

A

Urine concentrates 400-600mOsmol/kg

35
Q

What result of a 8hr fluid deprication test would lead you to diagnose Cranial DI?

A

Urine concentrates only after giving desmopressin

36
Q

What result of a 8hr fluid deprication test would lead you to diagnose Nephrogenic DI?

A

No concentraton of urine after desmopressin

37
Q

Potassium normal range

A

3.5-5.5 mmol/l

38
Q

Potassium - distribution in the body

A

Predominantly intracellular cation (only 2% is extracellular), maintained by active pumping from EC-> ICF by Na/K ATPase

90% freely exchangeable, the rest bound in RBCs, bone and brain tissue

39
Q

Hypokalaemia - below what value? causes?

A

below 3.5mmol/L

1-GI loss- Diarrhea, excess sweat
2-Renal loss - Hyperaldosteronism (Conn’s) - due to aldosterones effect on Na/K ATPase in kidneys causing the loss of K via urine and reabsorption of Na and water
. - Excess Cortisol (Cushings) - cortisol acts like aldosterone
3-Redistribution into cells - Insulin (increases activity of Na/K ATPase shifting K into cells), Beta-agonists (salbutamol)
4) rare - Hypomagnesesaemia - Mg needed for K processing

40
Q

Hyperkalaemia - above what value? causes?

A

> 5.5mmol/L

Less common than hypokalaemia, but more dangerous

Caused by excessive intake (almost always iatrogenic), movement out of cells or decreased excretion

41
Q

Causes of Hyperkalaemia due to excessive intake?

A

Oral (fastin)
Parenteral (via IV)
Stored blood transfusion

42
Q

Causes of Hyperkalaemia due to Transcellular Movement (ICF>ECF)?

A

Acidosis
Insulin shortage
Tissue damage/ catabolic state

43
Q

Causes of Hyperkalaemia due to Decreased excretion?

A 
Acute Renal Failure (oliguric phase)
CRF (late)
Potassium sparing diuretics (spironolactone)
Mineralocorticoid deficiency (Addisons)
NSAIDs, ACEi
44
Q

FUN FACT ABOUT POTASSIUM AND H+ IONS…

A

… H+ and potassium are intimately linked as one moves into the cells one moves out.

for every drop in pH of 0.1 there is an increase in K+ of 0.7

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