disorders of fluid and electrolyte balance

Question 1

Causes of hyponatremia - h20 retention

Answer 1

Usually H20 retention secondary to ecxcretion
(advanced renal failure. In absence of advanced renal failure, usually due to inability to suppress secretion of ADH

-can be because of hormonal changes such as cortisol deficiency, hypothyroidism

Question 2

Causes of hyponatremia

Answer 2

Primary polydipsia [excessive water drinking]- often schizophrenia

Question 3

What is pseudohyponatraemia

Answer 3

Artefactually low serum [Na+] resulting from volume displacement by massive hyperlipidaemia or hyperproteinemia

can be caused by hyperglycaemia or uncontrolled diabetes

Question 4

How does pseudohyponatraemia present as

Answer 4

Plasma osmolality is normal

Plasma [Na+] is apparently low

Question 5

Causes of hypernatremia

Answer 5

1) Mainly H20 loss (eg. diabetes insipidus, fever) + impaired thirst.
2) Na+ retention (eg. administration of hypertonic NaCl or NaHCO3-)

Question 6

What is ECF [K+] controlled by

Answer 6

Uptake of K+ into cell

Renal excretion and extrarenal losses

Question 7

What accounts for almost all K+ excretion

Answer 7

Abnormality in one/both of internal and external K+ balance in hypo/hyperkalaemia

Question 8

Effect of increase in K+

Answer 8

↑[K°] –>depolarise membrane –> more excitable; but persistent depolarisation inactivates Na+ channels –> decreased membrane excitability –> impaired cardiac conduction/muscle weakness (paralysis).

Question 9

Effect of decreased K+

Answer 9

low [K°] –> hyperpolarise membrane –> less excitable; but in cardiac myocytes –>membrane excitability due to removal of normal inactivation of Na+ channels

Question 10

What does intracellular K+ affect

Answer 10

Protein and glycogen synthesis

Question 11

What does a decrease in K+ reduce sensitivity to

Answer 11

ADH

Question 12

Physiological factors influencing transcellular distribution of K+

Answer 12

Na+/K+ ATPase
Catecholamines
Plasma [K+]
Exercise
Insulin

Question 13

Pathology al factors which influence transcelluler distribution of K+

Answer 13

Chronic diseases
Extracellular pH (decrease pH increases K+ etc)
Hyperosmolality (more water increases K+ movement out of cell)
Rate of cell breakdown

Question 14

What does lack of insulin and b2 adrenoceptor antagonism do to plasma K+

Answer 14

Impairs but does not prevent K+ movement into cells

Question 15

How do catecholamines influence trans cellular distribution of K+

Answer 15

B2 receptors increase K+ uptake into cells; activates Na+/K+ ATPase

Question 16

When might there be increased rate of cell breakdown which would lead to increase in K+ release

Answer 16

Severe trauma e.g. burns, rhabdomyolysis

Question 17

Causes of hypokalaemia

Answer 17

decreased net intake may contribute but rarely solely responsible

Increased entry into cells

Increased GI losses (vomiting diarrhoea)

Question 18

How can there be increased entry into cells which may cause hypokalaemia

Answer 18

Alkalosis

Insulin (diabetic hyperglycaemia- K+ depleted already)

B2 adrenoceptor activation (adrenaline, stress, hypoglycaemia or inhalers)

Increased urinary losses

Increased sweat loss

Question 19

What can cause increased urinary losses

Answer 19

Loop or thiazide like diuretics
Vomiting
Mineralocorticoid excess
Renal tubular acidosis
Rare hereditary disorders

Question 20

How can vomiting cause hypokalaemia

Answer 20

Initially KHCO3- lose, Na+ reabsorbed

Question 21

How can mineralocorticoid excess cause hypokalaemia

Answer 21

most often due to aldosterone-producing adrenal adenoma; usually results in metabolic alkalosis due to aldosterone stimulation of H+ATPase

Question 22

How does type 1 renal tubular acidosis cause hypokalaemia

Answer 22

Decreased distal H+ secretion

Therefore increased K+ secretion for electroneutrality as Na+ is reabsorbed

Question 23

How does type 2 renal tubular acidosis cause hypokalaemia

Answer 23

Decreased proximal HCO3- reabsorption

Therefore increased HCO3- loss in urine leads to increase in K+ secretion

Question 24

How can hypokalaemia cause renal dysfunction

Answer 24

Polyuria, polydipsia
Increased ammoniagenesis
Increased HCO3- reabsorption (intracellular acidosis_

Question 25

What can hypokalaemia contribute to

Answer 25

Maintenance of metabolic alkalosis

Question 26

Treatment of hypokalaemia

Answer 26

KCl, KHCO3 oral, i.v.

Question 27

what are causes of hyperkalaemia

Answer 27

Increased intake
Movement from cells into ECF
Decreased urinary excretion

Question 28

What causes movement of K+ from cells into ECF to cause hyperkalaemia

Answer 28

Pseudohyperkalaemia
Metabolic acidosis 
Insulin deficiency + hyperosmolality
Tissue catabolism-rhabdomyolysis
Badrenoceptor antagonism
Severe exercise

Question 29

What causes decreases urinary excretion

Answer 29

renal failure
Hypovolaemia
Hypoaldosteronism

Question 30

Treatment of hyperkalaemia

Answer 30

Antagonism of membrane actions

Increase K+ entry into cells

Removal of excess K+

Question 31

What is the antagonism of membrane actions

Answer 31

Giving patient Ca2+ for hyperkalaemia

Question 32

What do you give patient to increase K+ entry into cells

Answer 32

Insulin+ glucose
NaHCO3-
B2 adrenoceptor agonist (Salbutamol)

Question 33

How to remove excess K+

Answer 33

Diuretics
Cation-exchange resin
Haemodialysis/peritoneal dialysis

Question 34

What is acidosis

Answer 34

Hyperkalaemia

Question 35

What is alkalosis

Answer 35

Hypokalaemia

Question 36

What are the different types of renal tubular acidosis in relation to K+

Answer 36

Type 1- hypokalaemia
type 2- hypokalaemia
Type 3- hyperkalaemia