Fluid And Electrolytes

Question 1

How is osmolality taken

Answer 1

Measured with osmometer using principle of freezing point depression

Question 2

How is osmolarity taken

Answer 2

Calculated: 2Na + urea + glucose

Question 3

Osmolal gap formula?

Answer 3

Osmolality - osmolarity
(Increases when other osmoles increase)

Question 4

Normal osmolal gap?

Answer 4

<10

Question 5

Name 3 physiological methods in which ECF osmolality is restored when water is lost

Answer 5

• Stimulation of vasopressin (adh) release → renal water retention
• stimulation hypothalamic thirst centre → increased intake
• redistribution of water from ICF

Question 6

Define laboratory and clinical hyponatraemia

Answer 6

Lab <135 mmol/l
Clinical ≤ 125

Question 7

Name 2 causes pseudo hypo Na

Answer 7

• Excess lipids
• excess protein
(Will have normal osmolality)

Question 8

Normal sodium value?

Answer 8

135-145 mmol/l

Question 9

Clinical consequence of acute hypona?

Answer 9

Cerebral oedema
Symptoms range from nausea and vomiting, confusion, coma death

Question 10

Treatment hypervolaemic hyponatraemia?

Answer 10

Lasix and fluid restriction

Question 11

Treatment euvolaemic hyponatraemia?

Answer 11

Fluid restriction

Question 12

Treatment hypovolaemic hyponatraemia?

Answer 12

Saline rehydration
(True hypo Na )

Question 13

Cause of hyper osmolar hypo na?

Answer 13

High glucose

Question 14

Name 2 causes of hyponatraemia with urine sodium ≤ 30 mmol / L and decreased ECF volume

Answer 14

Sodium depletion:
• Gastrointestinal
• cutaneous

Question 15

Name 3 causes of hyponatraemia with urine sodium ≤ 30 mmol / L and increased ECF volume

Answer 15

Sodium and water excess (oedema)
• heart failure
. Liver cirrhosis
• nephrotic syndrome

Question 16

Name 2 causes of hyponatraemia with urine sodium > 30 mmol / L and decreased ECF volume

Answer 16

Sodium depletion
• adrenal failure
• renal salt wasting
• cerebral salt wasting
• diuretics

Question 17

Name 3 causes of hyponatraemia with urine sodium > 30 mmol / L and normal ECF volume

Answer 17

Water excess (no oedema)
• syndrome of inappropriate adh (diagnosis of exclusion)
• ckd
• excess iv fluid infusion

Question 18

Name 5 diagnostic criteria for syndrome of inappropriate adh

Answer 18

SIADH:

(Diagnosis of exclusion)

• serum euvolaemic: normal ECF volume

• > 100 urine osmolality: urine must not be maximally diluted (osmolality >100 mosm/kg)

• adrenal,thyroid function, kidney, normal

• drug not cause hypo Na

• hypo Na <135 and low serum osmolality <275

Continued natriunesis despite low plasma sodium, aldosterone secretion doesn’t increase

Question 19

Name 5 causes and diagnosis hypovolaemic hypernatraemia

Answer 19

Assess clinically: dehydrated

Water very low and sodium low, but high concentration

Do urine sodium

Urine Na >40: renal losses
• osmotic diuresis or diuretic use
• ATN polyuric disease
- AKI/CKD

Urine Na < 25: extra-renal losses
• GI LOSS: osmotic diarrhoea, git fistula
• DERM LOSS: sweating/burns

MOLE: Meds (diuretics), Osmotic diuresis, Excessive water loss, Low water intake

Question 20

Name 2 causes euvolaemic hypernatraemia

Answer 20

Clinically dehydrated.

Low water, normal sodium lab value but high concentration

Do urine:plasma osmolality

Urine osmolality <1:renal losses
• diabetes insipidus - central or nephrogenic (differentiate with desmopressin)

Urine osmolality >1: extra renal losses
• insensible losses

LED: Low water intake (extrarenal), Diabetes insipidus, Excess water loss

Question 21

Name 5 causes hypervolaemic hypernatraemia

Answer 21

Clinically oedema, overhydrated.

“Classic” because Na will be >145. And water high

• Hypertonic saline infusion
• iv naHco3 as emergency for severe metabolic acidosis
• overconcentrated formula milk
• hypertonic dialysis
• sea water ingestion
- hyperaldosteronism

Question 22

Name 4 trans cellular movement causes of hypo K

Answer 22

• alkalosis
• insulin administration
• refeeding syndrome
• increased k excretion

Question 23

Name 5 renal causes of hypo K

Answer 23

• Diuretics
• AKI: early diuretic phase
• renal tubular acidosis 1 and 2
• mineralocorticoid excess: primary and secondary aldosteronism, Cushing
• tubular (distal) disorders: batter syndrome, Liddle syndrome, Gitelman’s syndrome

Question 24

Name  2 extrarenal causes of hypo K

Answer 24

• diarrhea
• vomiting

Question 25

Treatment hypervolemic hyper na?

Answer 25

Furosemide (loop diuretic) and 5% dextrose (hypotonic fluid) iv Possibly dialysis if severe (Dextrose causes hyper osmolality so water moves intracellular to extra cellular, creating dilutional effect)

Question 26

Treatment euvolemic hyper na?

Answer 26

5% dextrose iv or water orally

Question 27

Treatment hypovolemic hyper na?

Answer 27

Isotonic saline slowly and 5% dextrose iv

Question 28

Name 6 factors that influence urinary potassium excretion

Answer 28

• Circulating aldosterone (cause hypo k in favour of sodium) • amount of sodium arriving at distal tubules • relative availability hydrogen and potassium of cells at distal tubules and collecting ducts • capacity of cells to secrete hydrogen ions (h and K go together) . Dietary K intake • intravascular volume (reduction stimulate aldosterone)

Question 29

Name 4 causes spurious ("false") hyperkalaemia

Answer 29

•Hamolysis . EDTA contamination • old sample • abnormal blood cells: leukemia, thrombocytosis

Question 30

Name 7 causes transcellular movement hyperkalaemia

Answer 30

• Acidosis • tissue damage (tumour lysis syndrome) • vigorous exercise . Decrease K excretion • AKI and CKD • K sparing diuretics . Mineralocorticoid deficiency: Addison's, aurenolectomy, hyporeninaemic hypoaldosteronism

Question 31

What is ADH, where produced and function

Answer 31

- ADH = vasopressin - posterior pituitary - main function = water reabsorption by increase aquaporin 2 channels on DCT and CD - stimulated by increased plasma osmolarity (high na) and to lesser extent low blood volume - also vasoconstriction by increase vascular resistance

Question 32

What is aldosterone, where produced and function

Answer 32

- Activated by RAAS (which is activated by low blood volume and pressure) and low Na or high K - adrenal cortex - activate eNAC channels and na/k ATP ase on DCT - reabsorb Na and water, excrete K

Question 33

What are natriuretic peptides, where produced and function

Answer 33

- BNP, ANP - heart - stimulated by high blood pressure and volume - inhibit renin and therefore RAAS by A) decrease sympathetic response B) afferent arteriole vasodilation → increase GFR → naturesis Ultimately inhibit aldosterone → decrease Na and H2O - also vasodilation