91. Abnormal serum sodium Flashcards
Approach to working out what is the cause of low sodium
- is it true hyponautraemia?
- What is their fluid status?
hypovolemic - more sodium out
euvolemic - more water in
hypervolemic - water retention>sodium retention - What is their urine osmolality?
high/not adequately responded - something going wrong at the level of the kidneys eg low alodosterone, high ADH, diuretics
low - kidneys working, problem is somewhere else
where is sodium found
main cation in ECF
how to know if it is true hyponautraemia?
Check serum osmolality
- in true hyponautraemis this will be low
- in pseudohyponautraemia this will be normal (hyperlipidaemia, hyperproteinemia)
- in hyperglycaemia this will be high
calcualte the osmolar gap
- 2Na + 2K + urea + glucose
- this should be <10mmol difference to serum osmolality
- if >10 pseudohyponautraemia
causes of hypovolemic hyponautraemia
too much sodium lost:
- decreased aldosterone = decreased reabsorption of sodium eg ADDISONS
- diuretics = decreased resorption of sodium
- sweating/vomiting/burns
- cerebral salt wasting
causes of euvolemic hyponautraemia
to much water in/retianed:
- SIADH
- water intoxication
- hypothyroidism
causes of hypervolemic hyponautraemia? mechanism?
heart failure
liver failure
nephrotic syndrome
fluid leaks out of intravasucalr space –> hypotension –> reduced perfusion to kidneys –> RAAS activation –> retain more water than sodium
how does hypothyroidism cause hyponautraemia
decreased CO –> decreased volume cirucalting to brain –> hypothalamus increased ADH –> dilutional hypoNa
define mild/moderate and severe hyponautraemia
mild: 130-134 mmol/L
moderate: 120-129 mmol/L
severe: < 120 mmol/L
when should someone with hyponautraemia be referred from priamry care?
Have acute onset (duration for less than 48 hours) or severe (serum sodium concentration of less than 125 mmol/L) hyponatraemia.
Are symptomatic.
Have signs of hypovolaemia.
early symptoms and late symptoms hyponautraemia
early symptoms may include: headache, lethargy, nausea, vomiting, dizziness, confusion, and muscle cramps
late symptoms may include: seizures, coma, and respiratory arrest
Management severe hyponautraemia/severe symptoms
hypertonic saline SLOWLY in HDU
eg NaCl 3%
management of hypovolemic hyponautraemia
IV fluids 0.9% NaCl trial
- if increased then this supports diagnosis of hypovolemic hyponautraemia
management of SIADH
fluid restrict to 500-1000ml per day
find and treat cause
tolvaptan (vasopressin antgaonist) initiated by a specialist endocrinologist and require close monitoring, for example 6 hourly sodium levels.
management of hypervolemic hyponautraemia
fluid restrict to 500-1000ml per day?
treat undelrying cause
complication of correcting sodium too fast
Osmotic demyelination syndrome (Central Pontine Myelinolysis)
It is usually a complication of long term severe hyponatraemia (< 120 mmols/l) being treated too quickly (> 10 mmol/l increase over 24 hours)
To avoid this, Na+ levels are only raised by 4 to 6 mmol/l in a 24-hour period
presentation osmotic demyelination syndorme
symptoms usually occur after 2 days and are usually irreversible: dysarthria, dysphagia, paraparesis or quadriparesis, seizures, confusion, and coma, patients are awake but are unable to move or verbally communicate, also called ‘Locked-in syndrome’
where is ADH produced? where is it secreted from?
Antidiuretic hormone (ADH) is produced in the hypothalamus and secreted by the posterior pituitary gland. It is also known as “vasopressin”.
can also be produced and released from ectopic sites eg small cell lung cancers
name some causes of SIADH
SIADH
Small cell lung tumours
Infection (particularly atypical pneumonia)
Abscess
Drugs (use SIADH cannot void)
Head injury
post-op from major surgery
Drugs:
SSRIs
Inhibitors (ACEi, PPI)
Antidepressants eg TCAs
Diuretics
Haloperidol
Cannot: carbamazepine
Void: vincristine
what do you think when someone has persistent hyponatraemia with no clear cause
suspect malignancy
Particularly in someone with a history of smoking, weight loss or other features of malignancy.
If malignancy is suspected the NICE CKS (March 2015) recommend a CT thorax/abodmen/pelvis and MRI brain to find the malignancy.
hypovolemia vs dehydration
Hypovolemia refers to a decreased volume of fluid in the vascular system with or without whole body fluid depletion. Dehydration is the depletion of whole body fluid. Hypovolemia and dehydration are not mutually exclusive nor are they always linked.
how to ddx between cerebral salt wating and SIADH
both can be caused by head injury
cerebral salt wasting - hypovolemic
SIADH - euvolemic
what kind of steroid is aldosterone, where is it produced?
mineralocorticoid
zona glomerulosa of the adrenal cortex
pathophysiology addison’s disease
Autoimmune destruction of the adrenal glands
no adrenal glands –>
- no aldosterone - low sodium, high potassium, high H+ (metabolic acidosis
- no cortisol so low glucose
symptoms of addisons
lethargy, weakness, anorexia, nausea & vomiting, weight loss, ‘salt-craving’
hyperpigmentation (especially palmar creases)*, vitiligo, loss of pubic hair in women,
