sodium Flashcards
What is the commonest electrolyte abnormality in hospitalized patients?
low na
What is the commonest electrolyte abnormality in hospitalized patients?
low na
what is hypona
<135
common causes of low na
HF
renal failure
hypovolaemia
ie excess extracellular water
which hormone controls water balance and how
ADH/vasopressin
act on V2 receptor in collecting duct
-> water retention through aquaporin-2 in distal part of tubule
V1 receptor on vascular smooth muscle -> vasoconstriction (higher conc)
What are the two main stimuli for ADH secretion?
Serum osmolality (mediated by hypothalamic osmoreceptors detect the increase in osmolarity = more ADH secreted) – if it increases then you need to hang onto water
Blood volume/pressure (mediated by baroreceptors in carotids, atria, aorta) – BP drop detected by baroreceptors = more ADH release = more water resorption
What are the two main stimuli for ADH secretion?
Serum osmolality (mediated by hypothalamic osmoreceptors detect the increase in osmolarity = more ADH secreted) – if it increases then you need to hang onto water
Blood volume/pressure (mediated by baroreceptors in carotids, atria, aorta) – BP drop detected by baroreceptors = more ADH release = more water resorption
What is the effect of increased ADH secretion on serum sodium?
hypoNa
What is the first step in the clinical assessment of a patient with hyponatraemia?
Clinical assessment of volume status - hypo/er/euvolaemic
* Pulse
* Mucous membranes
* BP – lying and standing
* Tissue turgor – pinch skin
* Urine output
* Confusion
What are the clinical signs of hypovolaemia?
Tachycardia
Postural hypotension
Dry mucous membranes
Reduced skin turgor
Confusion/drowsiness
Reduced urine output
Low urine Na+ less than 20 - most useful marker. Kidney best detector of hypovolaemia – hold onto water so less Na in urine and less urine. Note cant interpret if taking diuretics
What are the clinical signs hypervolaemia?
Raised JVP
Bibasal crackles (on chest examination)
Peripheral oedema
causes of hypoNa
hypovol - loss of na and water -> baroreceptor -> more ADH -> Increased water retention -> more water compared to salt
causes of hypoNa in hypervol
Cardiac failure: reduced heatrt contractility – low BP detected by baroreceptor =- more ADH = more water = low Na
Cirrhosis: excess NO = low BP (vasodilator) = baroreceptor = more ADH more water
Renal failure: not excreting excess water
What are the causes of hyponatraemia in a euvolaemic patient?
Hypothyroidism – less cardiac contractility, low bp
Adrenal insufficiency – less aldosterone, less cortisol
Syndrome of inappropriate ADH (SIADH) – released by tumour/drug – not a dx
causes of SIADH
CNS pathology – tumour stroke
Lung pathology
Drugs (SSRI, TCA, opiates, PPIs, carbamazepine)
Tumours
Surgery
ix in euvolaemic hypoNa
? Hypothyroidism: Thyroid function tests
? Adrenal insufficiency: Short Synacthen test or 9am cortisol
? SIADH: Plasma & urine osmolality (low plasma & high urine osmolality)
why euvolaemic in SIADH
water redistributed, and don’t have Na resorption. Retain more water – lead to stretch of atria = natriatic peptide released = lose Na in urine
dx of SIADH
No Hypovolaemia
No Hypothyroidism
No Adrenal insufficiency
Reduced plasma osmolality AND
Increased urine osmolality (>100) no reference range
How would you manage a hypovolaemic patient with hyponatraemia?
Volume replacement with 0.9% saline (NaCl)
Removes stim for excess ADH – replacing the blood volume
If they have SIADH and give saline – they retain excess water and you make it worse
How would you manage a hypervolaemic patient with hyponatraemia?
Fluid restriction
Treat the underlying cause
How would you manage a euvolaemic patient with hyponatraemia?
Fluid restriction
Treat the underlying cause
how do you treat severe hyponatraemia
med emergency
Reduced GCS
Seizures
Seek expert help (Treat with Hypertonic 3% (2.7%) saline) – only if reduced GCS or fitting because serum Na shouldn’t be corrected quickly
What is the most important point to remember while correcting hyponatraemia?
Na must NOT be corrected > 8-10 mmol/L in the first 24 hours
Risk of osmotic demyelination (central pontine myelionlysis)
quadriplegia, dysarthria, dysphagia, seizures, coma, death
Disrupts blood brain barrier, inflammatory cytokines
drugs to treat SIADH if water restriction is insufficient
Demeclocycline
* Reduces responsiveness of collecting tubule cells to ADH
* Monitor U&Es (risk of nephrotoxicity)
Tolvaptan
* V2 receptor antagonist
