hyponatraemia

Question 1

causes of hyponatraemia

Answer 1

dehydration
excessive free water intake (primary polydipsia)
increased release of ADH cause reabsorption of free water in the kidneys

Question 2

hypotonic hyponatreamia

Answer 2

low measured serum Na concentration and low serum osmolality (true hyponatraemia)

Question 3

hypovolaemic hypotonic hyponatraemia

Answer 3

low extracellular fluid volume
caused by
- acute or chronic renal failure with polyuria
- diuretics
- mineralocorticoid deficiency
- diarrhoea/vomting
- dermal fluid loss eg. burns
- third space fluid loss eg. peritonitis
- bleeding/heamorrhage

Question 4

euvolaemic hypotonic hyponatraemia

Answer 4

normal or minimal changes in extracellular fluid volume
causes
- SIADH
- medication use
- exercise associated hyponatraemia
- acute or chronic renal failure
- glucocorticoid deficiency
- severe hypothyroidism
- decreased salt intake
- water intoxication

Question 5

hypervolaemic hypototnic hyponatraemia

Answer 5

high extracellular fluid volume
caused by
- acute or chronic renal failure with low urine output
- congestiva heart failure
- liver corrhosis

Question 6

exercise associated hyponatraemia

Answer 6

euvolaemic hypotonic hyponatraemia
occurs up to 24 hours after prolonged exercise
ingestion os water in excess of fluid loss
non-specific symptoms eg. dizziiness, headache, nausea, vomtiing, bloating

Question 7

treatment of exercise associated hyponatraemia

Answer 7

oral hypertonic saline for mild symptoms
IV for severe symptoms

Question 8

hypertonic hyponatraemia

Answer 8

low measures Na and high serum osmolality
caused by
- hyperglycaemia
- IV radiocontast
- IV maannitol

Question 9

why does hyperglycaemia cause hyponatraemia

Answer 9

Glucose is osmotically active, causing intravascular hypertonicity in states of high blood glucose. This hypertonicity pulls water into the intravascular space, causing a decrease in sodium concentration.

Question 10

isotonic hyponatraemia

Answer 10

low measures serum Na concentration and normal serum osmolality
TURP syndrome
psaudohyponatraemia - asymptomatic laboritory artefact

Question 11

total body sodium in hypertonic hyponatraemia

Answer 11

Total body sodium is not decreased, but the water that shifts from the ICF to the ECF results in a dilutional drop in the measured serum sodium. Sodium does not need to be substituted. Instead, the additional osmotically active solute should be corrected (e.g., by decreasing blood glucose levels).

Question 12

severely symptomatic hyponatraemia

Answer 12

severity tends to correlate with extent of cerebral oedema
confusion, stupor, coma
seizures
ataxia
respiratory failure
other: malaise, lethargy, headache, nausea, vomiting

Question 13

mild symptomatic hyponatraemia

Answer 13

forgetfullness
gat disturbances
muscle weakness
malaise
headache
dizziness
fatgue
lethargy
nausea and vomitting

Question 14

diagnostic appraoch

Answer 14

1. confirm hyponatraemia - repeat BMP
2. exclude hyperglycaemia
3. check serum osmolality

continue diagnosis based on osmolality

Question 15

diagnostic approach for hypotonic hyponatraemia

Answer 15

urine osmolality
- dilute urine - ADH is suppressed
- concentrated urine - ADH is appropriately or inappropriately elevated
determination of volume status: to determine if ADH activity is appropriate eg. in response to low arterial blood volume or innapropriate eig. in response to SIADH
interpretation of FENa to dtermine if thee cause is renal or extrarenal

Question 16

what does ADH do

Answer 16

A posterior pituitary hormone that regulates blood pressure, fluid balance, and sodium balance by causing thirst, increased water reabsorption in the renal collecting ducts, and peripheral arteriolar constriction. ADH is released in response to an increase ≥ 1% in serum osmolality (primary stimulus), or an ECF volume contraction > 10% (secondary stimulus).

Question 17

determination of volume status

Answer 17

history - recent nausea/vomiting or haerrhage might suggest low effective arterial volume

Question 18

interpretation of UNa and FENa

Answer 18

UNa < 20–30 mEq/L and/or FENa < 1%: may suggest extrarenal loss of sodium (Low urine sodium concentration indicates either urine dilution secondary to excessive water intake or renal sodium retention in response to low effective arterial blood volume.)
UNa ≥ 20–30 mEq/L and/or FENa > 1%: may suggest renal loss of sodium (Elevated urine sodium may also reflect urine concentration due to inappropriately increased ADH.)

Question 19

lab studies for hypotonic hyponatraemia

Answer 19

TSH to evaluate for hypothyroidism
serum cortisol and CTH to evaluate for hypocorticolism and hypoaldosteronism
urine drug screen to evaluate for MDMA use
BNP to evaluate for CHF
urine chloride

Question 20

hypothyroidism

Answer 20

A condition in which the thyroid gland is underactive, which causes a deficiency of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). Typical clinical findings include fatigue, bradycardia, cold intolerance, constipation, and weight gain.

Question 21

hypocorticolism

Answer 21

A state of decreased production of glucocorticoids (e.g., due to adrenal insufficiency). Can cause weakness, fatigue, depression, decreased appetite, weight loss, nausea, vomiting, diarrhea, and abdominal pain.

Question 22

work up for hypertonic hyponatraemia

Answer 22

check serum glucose and calculate corrected sodium for hyperglycaemia
treat underlying cause

Question 23

workup for isotonic hyponatraemia or pseudohyponatraemia

Answer 23

normal Na concentration in whole blood sodium confirms pseudoyponatraemia
lipid panel or serum protein may be indicated

Question 24

rapid autocorrection of sodium

Answer 24

Once specific treatment is given (e.g., discontinuation of diuretics, corticosteroids for hypocortisolism), there is a high risk of rapid autocorrection causing a dangerous increase in sodium.
Avoid sodium overcorrection to minimize the risk of osmotic demyelination syndrome (ODS).

Question 25

treating chronic hyponatraemia without severe symptoms

Answer 25

slow correction of serum sodium levels to prevent overorrection and subsequent osmotic cell damage