sodium and water balance disorders

Question 1

what is the most common electrolyte abnormality seen in clinical practice

Answer 1

hyponatremia

Question 2

what kind of disorders are sodium disorders

Answer 2

disorders of water balance (not salt)

Question 3

clinical features of acute hyponatremia (4)

Answer 3

1. seizures
2. coma
3. resp distress
4. severe cerebral oedema

Question 4

clinical features of chronic hyponatremia

Answer 4

frequently mild/no symptoms
1. headache
2. restlessness
3. muscle cramps
4. N&V
5. lethargy
6. confusion and disorientation

Question 5

why is cerebral oedema not seen in chronic hyponatremia

Answer 5

adaptation minimises brain swelling

Question 6

what is osmotic demyelination syndrome

Answer 6

rapid correction of hyponatremia leads to central pontine myelinosis

rapid correction leads to astrocyte apop -> disruption of BBB + exposure to inflammatory cytokines -> osmotic demyelination

Question 7

if a pt has low serum sodium, and hyperglycaemia with normal corrected serum sodium what is the cause

Answer 7

hyperglycaemia-induced hyponatremia (pseudohyponatremia)

Question 8

what is the formula for corrected sodium

Answer 8

corrected sodium = measured sodium + 0.024(serum glucose - 100)

(hiller 1999)

Question 9

what is hypo-osmolar hyponatremia (4)

Answer 9

serum hyponatremia with:
1. NO hyperglycaemia
2. NOT post operative after prostate or uterine surgery
3. NO IVIG or mannitol received
4. no reason to suspect pseudohyponatremia (e.g. jaundice)

Question 10

what is hyper/iso osmolar hyponatremia

Answer 10

serum hyponatremia with NO hyperglycaemia but reason to suspect psuedohyponatremia and a nromal/high serum osmolality

Question 11

2 causes of hyper/iso osmolar hyponatremia

Answer 11

1. Transurethral resection of the prostate (TURP) syndrome
2. hysteroscopy
   associated with the absoption of irrigation solutions

Question 12

how should patients w pseudohyponatremia have their sodium measured

Answer 12

direct potentiometry

Question 13

how is hyponatremia treated in TURP syndrome (2)

Answer 13

depends on the degree
1. fluid restriction
2. furosemide
3. hypertonic saline - severe

Question 14

what is hypervolemic hyponatremia

Answer 14

enormous increase in total body water with a less significant increase in total body sodium -> Even though there’s more water overall, there’s a decrease in the effective circulating volume, the amount of blood flowing in the body -> ADH release leading to pure water retention -> aldosterone release -> retention of sodium -> water follows sodium -> the body retains even more water, so ultimately there’s a large increase in water, but a small increase in sodium, leading to hyponatremia

Question 15

what conditions is hypervolemia hyponatremia seen in

Answer 15

1. congestive heart failure
2. cirrhosis
3. nephrotic syndrome
   a lot of fluid leaks out of the blood vessels and into the interstitial space, causing oedema especially in the ankles

Question 15

what kindof hyponatremia does diahorrea and vomiting cause

Answer 15

hypovolemic hyponatremia - cells lining the gastrointestinal tract actually pump sodium ions into the digestive juices, but then those ions don’t get reabsorbed as they are removed in D&V

Question 16

what does hypo-osmolar hyponatremia with impaired GFR indicate

Answer 16

renal failure (i.e. hyponatremial secondary to CKD)

Question 17

what drugs can commonly cause hyponatremia (7)

Answer 17

1. thiazide /thiazide-like diuretics
2. carbamezepine
3. sulphonylureas
4. PPIs
5. SSRIs
6. ACEi/ARBs
7. opiates

Question 18

causes of hypovolemic hyponatremia with low urine sodium

Answer 18

extra-renal causes -> D&V, third space losses (fluid losses into spaces that are not visible, such as the bowel), diuretics

Question 19

what should be done if there is hypovolemic hyponatremia with normal urine sodium

Answer 19

infuse isotonic saline and remeasure urine sodium

Question 20

cause of hypovolemic hyponatremia with high urine sodium

Answer 20

renal loss

Question 21

what should be done in the case of renal loss induced hypovolemic hyponatremia

Answer 21

1. review medication and history
2. measure AM cortisol and ACTH stimulation test

Question 22

what is the cause of hypovolemia hyponatremia with low cortisol/positive ACTH stimulation test

Answer 22

primary adrenal insufficency

Question 22

what is cerebral salt wasting

Answer 22

a renal loss of sodium during intracranial disease leading to hyponatremia and a decrease in extracellular fluid volume -> disruption of the sympathetic nervous system leading to incr. stimulation to kidneys and incr sodium loss

Question 23

what should be done with hypo-osmolar hyponatremia but not signs of hypovolemia

Answer 23

measure urine osmolality

Question 24

causes of dilute urine Euvolemic hyponatremia (4)

Answer 24

1. adrenal insufficiency
2. polydipsia (and the drinking of water to compnesate)
3. beer potomania
4. tea and toast diet
5. ecstacy use
6. endurance event e.g. marathon

Question 25

what is beer potomania and how does it cause hyponatremia

Answer 25

a person who’s intake is almost entirely beer, with little-no flood consumption
1. beer is a low sodium fluid, consumption of only means there are less solutes in the blood
2. the kidneys require solutes (mainly sodium and urea which are usually break down products of protein) in order to produce urine
3. without the intake of solutes the kidneys can only excrete around 5L of water a day
4. additional water consumed w the beer will stay in the body and cause a drop in blood sodium levels

Question 26

causes of concentrated urine Euvolemic hyponatremia (4)

Answer 26

1. SIADH
2. hypothyroidism
3. glucocorticoid deficency

Question 27

what are people with beer potomania at risk of with treatment

Answer 27

rapid correction leading to neurological symptoms

Question 28

what should be used to slow the rate of sodium correction (thus avoiding too rapid correction)

Answer 28

IV desmopressin with dextrose

Question 29

treatment of hyponatremia

Answer 29

hypertonic saline