16b Electrolyte homeostasis

Question 1

What is the extracellular concentration of Na+?

Answer 1

140 mmol/L.

Question 2

What is the intracellular concentration of Na+?

Answer 2

10 mmol/L.

Question 3

What is the intracellular concentration of K+?

Answer 3

150 mmol/L.

Question 4

What is the extracellular concentration of K+?

Answer 4

5 mmol/L.

Question 5

Give two examples of isotonic fluid loss:

Answer 5

Blood.

Fistula fluid.

Question 6

What is the effect of isotonic fluid loss?

Answer 6

Loss from extracellular fluid.

No [Na+] change or fluid redistribution.

Question 7

Give an example of hypotonic fluid loss:

Answer 7

Insensible water loss.

Question 8

What is the effect of hypotonic fluid loss?

Answer 8

Greater loss form ICF than ECF.

Small increase in [Na]. Fluid redistribution.

Question 9

Give an example of isotonic fluid gain:

Answer 9

Saline drip.

Question 10

What is the effect of isotonic fluid gain?

Answer 10

Gain to ECF.

No [Na] change or fluid redistribution.

Question 11

Give an example of hypotonic fluid gain.

Answer 11

Water.

Dextrose.

Question 12

What is the effect of hypotonic fluid gain?

Answer 12

Greater gain in ICF than ECF.

Small decrease in [Na]. Fluid redistribution.

Question 13

What are the effects of ADH?

Answer 13

Decreases renal water loss.

Increases thirst.

Question 14

How is ADH status ascertained?

Answer 14

Osmolality measurement.
Urine greater than plasma then ADH active.
Urine much greater plasma then water retention present.

Question 15

What effect does RAAS have on renal Na retention?

Answer 15

Increases it.

Question 16

How is RAAS activation ascertained?

Answer 16

If urine osmolality is less than 10mmol/l, then RAAS is active.

Question 17

What are the causes of hyponatraemia? (11).

Answer 17

Diuretics.
Addison's.
Na losing nephritis.
SIADH (inappropriate ADH).
Drugs.
CRF.
D+V.
Skin loss.
Stress.
Post surgery.
Hypothyroid.

Question 18

What is the normal range for plasma [Na]?

Answer 18

135-145 mmol/L.

Question 19

What is the normal range for plasma [urea]?

Answer 19

3-8 mmol/L.

Question 20

What is the normal range for plasma [glucose]?

Answer 20

3.5 - 5.5 mmol/L.

Question 21

Name two causes of hypernatraemia:

Answer 21

Decreased water intake.

Osmotic diuresis.

Question 22

What is the normal range for plasma [K]?

Answer 22

3.6 to 5.0 mmol/L.

Question 23

Which values of plasma [K] are dangerous?

Why?

Answer 23

less than 3 mmol/L, more than 6 mmol/L.

Cardiac conduction defects, abnormal neuromuscular excitability.

Question 24

Why does serum potassium not represent body potassium?

Answer 24

Small proportion in plasma, very affected by ICF-ECF exchange. Dependant on total body mass.

Question 25

ICF-ECF exchange significantly affects plasma [K]. Name the four factors that may change the exchange.

Answer 25

Acidosis.
Insulin/glucose therapy.
Adrenaline.
Rapid cellular incorporation - TPN, leukaemia.

Question 26

How are potassium and hydrogen ions related?

Answer 26

Exchanged across cell membrane.

Both bind to same negatively charged proteins e.g. Hb.

Question 27

What effect does acidosis and alkalosis have on potassium levels?

Answer 27

Acidosis - K out of cells - hyperkalaemia.

Alkalosis - K into cells - hypokalaemia.

Question 28

What are the causes of hyperkalaemia? (4).

Answer 28

Renal failure.
Acidosis.
Mineralocorticoid dysfunction: adrenocortical failure, minerocorticoid resistance (spironolactone).
Cell death during cytotoxic therapy.

Question 29

How is hyperkalaemia treated? (4)

Answer 29

Correct acidosis.
Give glucose and insulin.
Ion exchange resins.
Dialysis.

Question 30

What are the causes of hypokalaemia? (5)

Answer 30

Low intake.
Increased urine loss (diuretics, dysfunction).
GIT losses (D+V, fistulae).
Alkalosis.
Insulin/glucose therapy.

Question 31

What are the effects of a [K] less than 2.5mmol/l?

Answer 31

Lethargy, muscle weakness, heart arrhythmias.
Polyuria.
Alkalosis (increased renal HCO3- production).

Question 32

What is the treatment of hypokalaemia?

Answer 32

Supplementation orally or IV.

Question 33

When should potassium levels be routinely monitored? (4)

Answer 33

Diuretic therapy.
Digoxin use.
Compromised renal function.
In support of IV resuscitation.