sodium and water balance disorders Flashcards
what is the most common electrolyte abnormality seen in clinical practice
hyponatremia
what kind of disorders are sodium disorders
disorders of water balance (not salt)
clinical features of acute hyponatremia (4)
- seizures
- coma
- resp distress
- severe cerebral oedema
clinical features of chronic hyponatremia
frequently mild/no symptoms
1. headache
2. restlessness
3. muscle cramps
4. N&V
5. lethargy
6. confusion and disorientation
why is cerebral oedema not seen in chronic hyponatremia
adaptation minimises brain swelling
what is osmotic demyelination syndrome
rapid correction of hyponatremia leads to central pontine myelinosis
rapid correction leads to astrocyte apop -> disruption of BBB + exposure to inflammatory cytokines -> osmotic demyelination
if a pt has low serum sodium, and hyperglycaemia with normal corrected serum sodium what is the cause
hyperglycaemia-induced hyponatremia (pseudohyponatremia)
what is the formula for corrected sodium
corrected sodium = measured sodium + 0.024(serum glucose - 100)
(hiller 1999)
what is hypo-osmolar hyponatremia (4)
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)
what is hyper/iso osmolar hyponatremia
serum hyponatremia with NO hyperglycaemia but reason to suspect psuedohyponatremia and a nromal/high serum osmolality
2 causes of hyper/iso osmolar hyponatremia
- Transurethral resection of the prostate (TURP) syndrome
- hysteroscopy
associated with the absoption of irrigation solutions
how should patients w pseudohyponatremia have their sodium measured
direct potentiometry
how is hyponatremia treated in TURP syndrome (2)
depends on the degree
1. fluid restriction
2. furosemide
3. hypertonic saline - severe
what is hypervolemic hyponatremia
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
what conditions is hypervolemia hyponatremia seen in
- congestive heart failure
- cirrhosis
- nephrotic syndrome
a lot of fluid leaks out of the blood vessels and into the interstitial space, causing oedema especially in the ankles
what kindof hyponatremia does diahorrea and vomiting cause
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
what does hypo-osmolar hyponatremia with impaired GFR indicate
renal failure (i.e. hyponatremial secondary to CKD)
what drugs can commonly cause hyponatremia (7)
- thiazide /thiazide-like diuretics
- carbamezepine
- sulphonylureas
- PPIs
- SSRIs
- ACEi/ARBs
- opiates
causes of hypovolemic hyponatremia with low urine sodium
extra-renal causes -> D&V, third space losses (fluid losses into spaces that are not visible, such as the bowel), diuretics
what should be done if there is hypovolemic hyponatremia with normal urine sodium
infuse isotonic saline and remeasure urine sodium
cause of hypovolemic hyponatremia with high urine sodium
renal loss
what should be done in the case of renal loss induced hypovolemic hyponatremia
- review medication and history
- measure AM cortisol and ACTH stimulation test
what is the cause of hypovolemia hyponatremia with low cortisol/positive ACTH stimulation test
primary adrenal insufficency
what is cerebral salt wasting
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
