Electrolyte abnormalities Flashcards
plasma sodium concentration
most often due to water levels rather than lack or excess of sodium
hyponatraemia
psuedohyponatraemia - increased protein in the blood giving a false sodium read
sodium depletion
excess water intake
reduced renal free water clearance
can be treated with a fluid restriction to prevent further dilution of the sodium concentration
severity of symptoms will depend on: biochemical severtity rate of change - chronic low Na+ can be tolerated well adaptive capacity co-morbidities
SIADH
commonly an incorrect reflex diagnosis
not maximally diluting urine
retaining water
exclude adrenal failure, oedema
adaptation to hyponatraemia
oedema
inorganic osmolyte loss
slow adaptation
oedema improves
inappropriate management of fluid replacement - case example
can cause dilutional hyponatraemia if too much given fluid restriction didn't correct low Na+ give normal saline Na+ continues to fall GCS falling CT showed diffuse cerebral oedema --> death
over-rapid correction
low Na+ treated with small dose concentrated Na+ IV fluids
become hypernatremic
leads to osmotic demyelination syndrome
necrosis of the myelin
osmotic demyelination syndrome
demyelination
necrosis
treatment of hyponatraemia
exclude hypernatraemia, pseudohyponatraemia
do they have severe symptoms ie coma/seizure?
yes: hypertonic saline immediately
no: urine osmolality
think about diagnosis
treat cause
diagnosis
hypotonic hyponatraemia urine osmolality low: primary polydipsia inappropriate IV fluids low Na intake
high: measure urine sodium low: low effective arterial volume, heart failure, cirrhosis, nephrosis low: diuretics/ACEi SIADH, hypoadrenalism, vomiting
hypernatraemia
most commonly:
dehydration in elderly frail patients
excess Na+ IV therapy
hypokalaemia
CV: always perform ECG predisposition to digoxin toxicity neuromuscular: tetany and pain renal and electrolyte endocrine and metabolic
ECG: T-wave inversion
hyperkalaemia
CV neuromuscular: paraesthesia, weakness, paralysis renal electrolyte endocrine: increased insulin secretion
ECG: T-wave tenting. broadened complexes, reduced p waves, sine wave arrest, pre-arrest
K distribution
96% intracellular
Na/K ATPase
influenced by pH, metabolism, hormones, cell growth. cell volume
largely stored in muscle. also in liver and red cells
rhabdomyolysis can lead to increased K+ n the blood
crush injuries also raise K+ from intracellular space
hyperkalaemia
b-agonists eg salbutamol and insulin will drive K+ into the cells
in DKA, there is efflux of K+ from intracellular space
will lead to depletion of body K+, but a high plasma K+
treat with insulin and dextrose, and monitor glucose
renal K+
most absorbed in the PCT
thick ascending limb is the main control point
high K+ increase the rate of aldosterone, which is secreted and retains Na+ in exchange for K+
increased K+ in acidotic states
