Endocrine - Sodium Flashcards
What are the usual ways that sodium levels are regulated by the body?
1) Osmoregulation and ADH release
- central osmoreceptors express transient receptor potential vanilloid 1 (TRPV1)
- peripheral osmoreceptors express TRPV4
- -> osmotically activated to produce ADH
2) Baroregulation
- stretch sensitive receptors in LA, carotid sinus and aortic arch
- -> increased stretch causes afferent impulses that INHIBIT ADH release
3) In the kidney:
- ADH regulates permeability of apical membrane by insertion of AQP2 cannels
Central osmoreceptors involved in regulation of sodium balance have which receptor?
central osmoreceptors express transient receptor potential vanilloid 1 (TRPV1)
Peripheral osmoreceptors involved in regulation of sodium balance have which receptor?
peripheral osmoreceptors express TRPV4
How to correct Na for glucose?
Add 2.4 to Na for every 5.5 rise above glucose
ie: corrNa = measured + (glucose-5.5)/5.5
What is the calculated serum Osm?
=2xNa + glucose + urea
What is the osmolar gap?
= measured Osm - calculated Osm
** if >10 then presence of unmeasured osmotically active particles
Causes of a non-hypotonic hyponatraemia?
‘Effectve’ osmoles:
- hyperglycaemia
- mannitol
- radiocontrast media
- maltose
‘Ineffective’ osmoles:
- urea
- alcohols
- ethylene glycol
‘Pseudohyponatraemia
- triglycerides, hypercholesterol, high protein
- IVIG
- Monoclonal gammopathies
What are causes of hyponatraemia with LOW URINE OSMOLALITY <100mOsm/kg
Primary polydipsia
Low solute intake
Beer potomania
Evaluating hyponatramia: if urine >100mOsm/kg and LOW urine Na <30
If expanded ECF:
- heart failure
- liver cirrhosis
- nephrotic syndrome
If reduced ECF:
- diarrhoea/vomiting
- 3rd spacing
- remote diuretics
Evaluating hyponatrameia: if urine has urine Na >30 with NO diuretic/kidney disease
ECF reduced
- vomiting
- primary adrenal insufficiency
- renal salt wasting
- cerebral salt wasting
- occult diuretics
ECF NORMAL
- SIADH
- Secondary adrenal insufficiency
- Hypothyroidism
- Occult diuretics
Management of SEVERE hyponatraemia
1) Hypertonic saline (150mL 3% saline over 20 minutes) then repeat Na whilst running the next 150mL.
Repeat until 5mmol increase in Na
2) If symptoms improve with the 5mmol increase in Na:
- stop the 3% saline
- give IV normal saline SLOWLY with repeat Na at 6 hours
When trying to correct severe hyponatraemia what should the limits to increases be?
- limit increasing Na to maximum 10mmol in 24 hours, then aim 8mmol increase every 24 hours afterwards until Na=130
What happens if sodium level is overcorrected in management of hyponatraemia?
- cease saline
- consider IV dextrose
- can use desmopressin to prevent ongoing correction once increased by >=12mmol
What are the risk factors for central pontine demyelination in correcting hyponatraemia?
Alcohol (MAJOR RF!)
Younger patients
Hypokalaemia
When does central pontine demyelination occur in correcting hyponatraemia?
Symptom onset 2-6 days post presentation
