Fluid and Electrolyte Balance

Question 1

What is the normal serum range for sodium?

Answer 1

135-145mmol/L.

Question 2

Sodium excretion is regulated by what 3 things?

Answer 2

Renin-angiotensin system. Natriuretic peptides. Intrinsic renal mechanisms.

Question 3

What makes up extracellular fluid?

Answer 3

Interstitial fluid. Plasma.

Question 4

What organ produces angiotensinogen?

Answer 4

Liver.

Question 5

What organ produces renin?

Answer 5

Kidneys.

Question 6

Where is Angiotensin converting enzyme (ACE) found?

Answer 6

Lungs.

Question 7

Give 2 effects of Atrial Natriuretic Peptide (ANP).

Answer 7

Reduction in release of renin. Dilatation of afferent arteriole (more filtrate forced out). Increased loss of sodium ion in urine.

Question 8

Give 2 symptoms of hypovolaemia.

Answer 8

GI losses. Thirst. Lethargy. Dizziness. Confusion. Reduced urine volume.

Question 9

Give 2 symptoms of hypervolaemia.

Answer 9

Breathlessness. Peripheral oedema. Weight gain. Abdominal floating.

Question 10

What characterizes a patients as being hyponatraemic?

Answer 10

Na less than 135mmol/L.

Question 11

What are the three types of hyponatraemia?

Answer 11

Hypovolaemia hyponatraemia. Euvolaemia hyponatraemia. Hypervolaemia hyponatraemia.

Question 12

Give 2 causes of Hypervolaemia hyponatraemia?

Answer 12

Congestive heart disease. Cirrhosis. Nephrotic syndrome.

Question 13

Give 2 causes of Hypovolaemia hyponatraemia?

Answer 13

GI losses e.g. vomiting, diarrhoea. Medications e.g. diuretics. Cerebral salt wasting.

Question 14

What is Hypovolemic hyponatremia?

Answer 14

Small total body water, large sodium ↓.

Question 15

What is Hypervolemic hyponatremia?

Answer 15

Total body water ↑, small sodium ↑.

Question 16

What is Euvolemic hyponatremia?

Answer 16

↑ body water, no body sodium change.

Question 17

Give 2 causes of Euvolemic hyponatremia?

Answer 17

Diluted urine - adrenal insufficiency, hypothyroidism, drinking too much (polydipsia). Undiluted - syndrome of inappropiate Anti-diuretic hormone (SIADH).

Question 18

How is Euvolemic hyponatremia seprated?

Answer 18

Diiluted urine. Concentrated urine.

Question 19

Give 2 symptoms of hyponatraemia.

Answer 19

Muscle cramps. Vomiting. Nausea.

Question 20

What is a severe complication of hyponatraemia?

Answer 20

Cerebral oedema - confusion, death, coma. Respiratory failure.

Question 21

What percentage of our body is water?

Answer 21

60%.

Question 22

1/3 of our body water is intracellular or extracellular?

Answer 22

Extracellular.

Question 23

What treatment is recommended for a euvolaemic hyponatraemia patient?

Answer 23

Fluid restriction.

Question 24

Why is excessive sodium level correction dangerous?

Answer 24

Can lead to cerebral pontine myelinolysis (rapid sodium, water shifts → myelin-loss in pons).

Question 25

What characterizes hypernatraemia?

Answer 25

Sodium greater than 145mmol/L.

Question 26

What causes of hypernatraemia?

Answer 26

Water loss greater than sodium loss. Sodium increases.

Question 27

What can cause un-replaced water losse resulting in hypernatraemia?

Answer 27

Insensible sweat losses. Nephrogenic diabetes (receptors in kidneys don’t respond to ADH). Central diabetes insipidus (damage to hypothalamus therefore less ADH produced). Damage to thirst centre.

Question 28

What can cause sodium overload resulting in hypernatraemia?

Answer 28

Administration of high salt load.

Question 29

Give 2 symptoms of hypernatraemia.

Answer 29

Thirst. Weakness. Seizures. Coma.

Question 30

What characterizes hypokalaemia?

Answer 30

Low potassium levels in the blood < 3.5mEq/L

Question 31

Give 3 causes of hypokalaemia?

Answer 31

Decreased K intake. Increased entry into cells from blood. Increased losses e.g. GI (vomiting), urine.

Question 32

What is responsible for the decrease in serum K in hypokalaemia?

Answer 32

Increased kidney excretion (urine losses) - hyperaldosteronism, drugs (e.g. loop diuretic), renal tubular defects. Increased sweat production (e.g. exercise). Increased gastrointestinal production e.g. vomiting, diarrhoea. Insulin overdose in Type I diabetes; excess insulin → increases sodium/potassium pump action.

Question 33

What is the effect of hypokalaemia on an ECG?

Answer 33

Flattening of T waves. Depression of ST segment. Development of U wave. Widening QRS complex.

Question 34

Give 2 symptoms of hypokalaemia.

Answer 34

Muscle weakness. Arrhythmia. Constipation.

Question 35

What characterizes hyperkalaemia?

Answer 35

High potassium levels in blood > 5.5 milliequivalents/liter (mEq/L).

Question 36

Give 2 causes underlying hyperkalaemia.

Answer 36

Increased potassium released from cells. Reduced urinary excretion.

Question 37

What causes increased potassium release from cells?

Answer 37

Uncontrolled Type I diabetes - Lack of insulin→ decreases sodium/potassium pump action. Acidosis - excess hydrogen ions move into cells via ion transporters that exchange hydrogen ions for potassium ions. Massive cell lysis e.g. tumor lysis syndrome, rhabdomyolysis, massive hemolysis. Drugs e.g. Beta2-adrenergic antagonists, digoxin toxicity. Exercise - Cellular ATP consumed → potassium channels open.

Question 38

What decreases potassium excretion from kidneys?

Answer 38

Adrenal insufficiency → primary hypoaldosteronism, so principal cells secrete less potassium. Drugs - Renin inhibitors, angiotensin converting enzyme (ACE) inhibitors, angiotensin II receptor antagonists, potassium-sparing diuretics, nonsteroidal anti-infl ammatory drugs (NSAIDs), cyclosporine, trimethoprim-sulfamethoxazole.

Question 39

Give 2 symptoms of hyperkalaemia.

Answer 39

Paraesthesiae (pins and needles). Muscle weakness - paralysis. Arrhythmias.

Question 40

What is the effect of hyperkalaemia on an ECG?

Answer 40

Tall peaked T waves. Loss of p waves. Widened QRS complex. Depressed ST segment.

Question 41

Give 2 treatments for hyperkalaemia.

Answer 41

Calcium to stabilize myocardial cell membranes. Insulin with dextrose - increase potassium shift into cells. Loop diuretics - increase potassium excretion in kidneys.