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Water And Electrolyte Metabolism Flashcards

1
Q

What is the total body water?

A

42L

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2
Q

What percentage of body weight is taken up by water in men?

A

About 60%

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3
Q

What percentage of body weight is taken up by water in women?

A

About 55%

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4
Q

What percentage of body weight is taken up by water in children?

A

75-80%

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5
Q

What percentage of water is in the ICF❓

A

66%

28L

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6
Q

What percentage of water is in the ECF❓

A

33%

14L

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7
Q

What percentage of water is in the plasma❓

A

8%

11L in ISF
3.5L in plasma

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8
Q

List the electrolyte composition of cations:

  1. Na
  2. K
  3. Ca
  4. Mg

In plasma

A

Na- 142mmol/L
K- 4mmol/L
Ca- 2.3mmol/L
Mg- 1mmol/L

Total cations- 150mmol/L

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9
Q

List the electrolyte composition of anions:

  1. Cl
  2. HCO3
  3. Phosphates
  4. Sulphates
  5. Proteins

In plasma

A
  1. Cl- 103mmol/L
  2. HCO3-27mmol/L

Measured anions- 130mmol/L

3,4,5- Unmeasured anions

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10
Q
  1. The anion gap in health is measured using which formula?
  2. What range is healthy?
  3. A derangement from this range might signify?
A
  1. Cations-measured anions
  2. 6-20mmol/L
  3. Lactic acidosis
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11
Q

List the electrolyte composition of cations:

  1. Na
  2. K
  3. Ca
  4. Mg

In ICF

A

Na- 12mmol/L

K- 156mmol/L

Ca- 1mmol/L

Mg- 13mmol/L

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12
Q

List the ICF anions

A

Proteins

Phosphates

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13
Q

Total body osmolality?

A

285mmol/kg

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14
Q

Total ECF osmolality?

A

282-295mmol/kg

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15
Q

Arginine vasopressin is secreted in response to❓

What is it’s function❓

A

⬆️osmolality

⬆️water retention by the kidneys
⬇️urine production

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16
Q

What electrolytes maintain ECF osmolality❓

A 
Na
Cl
HCO3 
Glucose
Urea
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17
Q

What electrolytes maintain ICF osmolality❓

A

K

Phosphates

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18
Q

What electrolytes maintain ISF osmolality❓

A

Colliod osmotic pressure/oncotic pressure by plasma proteins

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19
Q

What should you watch out for in assessing a patient for fluid therapy❓

A

History

Cardiac/Renal/Liver disease

Vomiting/Diarrhea

Nausea, headache, confusion

Fever, nasogastric suction, surgical drains, fistulae, artificial ventilation

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20
Q

What would you examine for in assessing a patient for fluid therapy❓

A
  1. Plasma volume:
    BP, pulse, JVP, CVP
  2. ISF volume- edema
  3. ICF volume-look for evidence of cerebral dysfunction
  4. Skin turgor
  5. Urine output
  6. Mucous membranes
  7. Level of consciousness
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21
Q

Describe the Na distribution in the body

A

In a 70kg man

•Total Na- 3700mmol

  • 75% is exchangeable
  • 25% isn’t exchangeable(in bone)
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22
Q

How much Na is taken in❓

How much Na sodium is excreted❓

A

100mmol/day-300mmol/day (in Western diets)

5mmol/L

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23
Q

What regulates Na output❓

A

Aldosterone- ⬇️Na output by ⬆️ Na reabsorption

Atrial Natriuretic peptide- ⬆️Na output

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24
Q

What is hyponatreamia?

A
  1. Fall in plasma Na below the reference range of 135-145mmol/L

⬇️Na
OR
⬆️Water

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25
Q

What are the 2 broad classifications❓

A
  1. Edematous Hyponatraemia:
    •Congestive Heart Failure CCF
    •Nephrotic syndrome
    •Inappropriate IV saline
  2. Non-edematous hyponatraemia:
    •SIAD
    •Renal failure
    •⬆️intake
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26
Q

How is hyponatreamia treated?

A

Correction of Na loss

Diuretics

Fluid restriction

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27
Q

How is hyponatreamia diagnosed?

A

Hypotension

Tachycardia

28
Q

Hyponatraemia due to Na loss from GI can be seen in?

A

Vomiting
Diarrhea
Fistula

29
Q

Hyponatraemia due to Na loss from urine can be seen in?

A

Aldosterone deficiency- addison’s disease (hypocortisolism)

Aldosterone antagonists-Spironolactone or triamterine

30
Q

Speak briefly about SIAD

A
  • Normal total body sodium
  • ⬆️secretion of ADH
  • ⬆️Water retention
  • Leads to non edematous hyponatraemia
•Can be encountered in:
Malignancies 
Infections
Trauma
Carcinoma of the lungs
Head injury

Or
Reduction in circulating blood volume
Nausea and vomiting
Pain

•Could be drug induced eg thiazide diuretics

31
Q

What is hypernatreamia❓

A

Na>135-145mmol/L

32
Q

What are the causes of hypernatreamia❓

A
  1. Water depletion as seen in dehydration
  2. Water and sodium depletion in diarrhea, vomiting
  3. Excess Na intake or retention seen in Conn’s syndrome or Cushing’s syndrome (hypercortisolism)
33
Q

What is the clinical presentation of hypernatreamia❓

A

Dehydration in water loss

Increased JVP and pulmonary edema as seen in fluid overload

34
Q

How is hypernatreamia treated?

A

Give oral fluids slowly

Give 5% dextrose slowly

35
Q

Describe the K distribution in the body

A

Total body K- 3600mmol

98% intracellular

5% extracellular

36
Q

How much K is taken in❓

How much K sodium is excreted❓

A

Variable. 30-100mmol/day

Variable, mostly by kidneys

37
Q

What stimulates cellular uptake of K❓

38
Q

What is hypokalamia?

39
Q

What are the clinical effects of hypokalamia?

A

Severe weakness
Hyporeflexia
Cardiac arrhythmias

Increased sensitivity to digoxin

40
Q

What are the ECG changes in hypokalamia?

A

Flattened T waves

Prominent U waves

41
Q

What are the causes of hypokalamia?

A

GIT losses: vomiting, diarrhea, fistula

Renal losses- renal disease, diuretic therapy, ⬆️aldosterone production

Drug induced- thiazide diuretics, corticosteroids, cabenoxolone

42
Q

How is hypokalemia treated?

A
  1. Oral k supplements
  2. IV potassium-
    🚫>20mmol/h under ECG monitoring
43
Q

What is hyperkalamia?

A

K>5mmol/L
>7mmol/L- risk of cardiac arrest

•Commonest and most serious electrolyte emergency

44
Q

What are the clinical features of hyperkalamia?

A

Muscle weakness

45
Q

What are the ECG changes in hyperkalamia?

A

Widened QRS complex

Peaked T waves

46
Q

What are the causes of hyperkalamia?

A

Renal failure/⬇️GFR

Mineralocorticoid deficiency:
Addison’s disease
Aldosterone antagonists like spironolactone or triamterene

Acidosis

Potassium released from damaged cells

Artefactual increase in hemolysed serum

47
Q

How would you treat hyperkalamia?

A

Infusion of insulin and glucose

Infusion of sodium gluconate

Dialysis

In crush injuries- ABC (Airway, Breathing, Circulation)

Cation exchange resin like resonium A

48
Q

What fluids are used in IV fluid therapy❓

A
  1. Water- 5% dextrose
  2. Isotonic NaCl- 0.9% NaCl
  3. Plasma/Whole blood
  4. 1.26% sodium bicarbonate
  5. Potassium supplements
49
Q

What are the sources of hydrogen ion in the body❓

A

Metabolism

Oxidation of sulphur-containing amino acids of proteins ingested as food

As dissolved CO2 in blood

50
Q

What is the reference range of H+ in the body❓

A

35-45nmol/L

•<20 and >120nmol/L is not compatible with life

51
Q

How is H+ managed in terms of excretion❓

A
  1. Through buffers:
    •a solution of the salt of a weak acid which is able to bind hydrogen ions
    •Blood buffers- CHO3, Hb, proteins
    •Urinary buffers- Phosphate, NH4+
  2. Through renal excretion bound to urinary buffers
52
Q

Describe how bicarbonate reabsorption is achieved❓

A

Refer to photos

53
Q

How is bicarbonate regeneration achieved❓

A

Refer to photos

54
Q

Describe the transport of carbon dioxide

A

Refer to photos

55
Q

List the arterial blood gas values for:

  1. H+
  2. HCO3
  3. PCO2
  4. PO2
A
  1. H+ - 35-46nmol/L
  2. HCO3- 22-30mmol/L
  3. PCO2- 4-6kP (36-46mmHg)
  4. PO2- 11-15kP (85-105mmHg)
56
Q

Respiratory disorders directly affect❓

57
Q

What happens in metabolic acidosis❓

A

H is high or normal

HCO3 is always low

58
Q

Metabolic acidosis can occur in what disease states❓

A

Renal disease
Diabetic ketoacidosis
Lactic acidosis

59
Q

What happens in respiratory acidosis❓

A

H is high or normal

PCO2 is always high

60
Q

Acute respiratory acidosis is not a medical emergency

True or false❓

61
Q

Respiratory acidosis can occur in what disease states❓

A

Airway obstruction

Respiratory centre depression

Lung disease

Neuromuscular disease eg poliomyelitis

Extrapulmonary thoracic dx like flail chest

62
Q

What happens in respiratory alkalosis❓

A

Occurs in conditions when respiration is stimulated or is no longer subject to feedback control

63
Q

What could cause respiratory alkalosis❓

A

Mechanical overventilation

Hysterical overbreathing

⬆️Intracranial pressure

Hypoxia

64
Q

What happens in metabolic alkalosis❓

A

H is depressed

HCO3 is raised

PCO3 is raised (respiratory compensation)

65
Q

What could cause metabolic alkalosis❓

A

Prolonged vomiting

Nasogastric suction
Conn’s syndrome

Clinical Pathology (6 decks)

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