Sodium Flashcards
What is the underlying pathogenesis of true hyponatramia?
Generally caused by excess extra-cellular water (not loss of salt)
What triggers cause ADH secretion?
Mainly
1. Increased serum osmolality
2. Decreased Blood volume/ receptor pressure
How does ADH cause increased water reabsoprtion?
Works on V2 receptors causing insertion of Aquaporin 2 channels
What are clinical signs and symptoms of hypovolaemia?
What is the most useful indicator?
Low urine Na+ (under 20) (will come up in exams)
–> if hypovolaemia, kidneys will hold on to soidim and therefore water, not interpretable in diuretics
- Tachycardia
- Postural hypotension
- Dry mucous membranes
- Reduced skin turgor
- Confusion/drowsiness
- Reduced urine output
What are the causes of hypovolaemia hyponatraemia?
**Generally salt-loosing conditions **
Diarrhoea
Vomiting
Diuretics
Salt losing nephropathy
+ Can be due to Addioson’s
This is a 2 step process
1. Salt and Water loss
2. Detection of water loss –> Increased retention of fluid via ADH (increased ADH secretion) –> More retention of water than sodium –> hyponatramia despite hypovolaemia
What are the causes of hypervolaemic hyponatraemia?
- Cardiac failure (with stimmulation of baroreceptors due to Low BP)
- Cirrhosis (patients have excess NO –> hypotension –> increased absorbtion)
- Nephrotic syndrome
–> everything that can cuase fluid overload
What are the cuases of Euvolaemic Hypovolaemia?
All the endocrine causes
Hypothyroidism (due to reduced cardiac contractility)
Adrenal insufficiency (due to lack of hormones - mineralcoirticoids)
SIADH
What are the causes of SIAD?
- CNS pathology (Brain)
- Lung (paraneoplastic Small Cell, TB, pneumonia, abscess)
- Drugs (SSRI, TCA, opiates, PPIs, carbamazepine)
- Tumours (lung + pancreas, prostate, lymphoma)
- Surgery
What is the expected blood osmolality in hyponatraemia?
Usually all are Hypoosmolar (because osmolality is calculated from sodium)
Osmolarity = 2(Na+ + K+) + urea + glucose
What investigation is most useful in diagnosing hypovolaemic hyponatreamia?
Urine Osmolality
If >20 –> due to your nomal causes of hypovolaemia (diarrhoea, vomiting, sweat, burns) –> Body tries to retain salt + water (concentrated)
If >20:
* Adrenocortical deficiecy
* cerebral salt waisting
* renal failure
* diuretics (cannot be interpreted)
How can SIDAH be diagnosed?
Exclusion of other causes
No Hypovolaemia
No Hypothyroidism –> Normal TFT
No Adrenal insufficiency –> Normal short synACTen
- **Reduced plasma osmolality AND (because low sodium)
- Increased urine osmolality (>100) (because high reabsorbtion)**
What is the management of hypovolaemic hyponatraemia?
0.9% Saline
–> Decreases in the trigger for ADH secretion (hypotension)
How do you treat hypervolaemic hyponatraemia?
- Fluidrestrict+/-diuresis
- treat the underlying cause
- Cirrhosis usually will require specialist input
What is the side-effect of rapid correciton of hyponatramia?
What is the aim for the rate of Hyponatraemia?
central pontine myelinolysis
By no more than 8-10 mmol/L per 24 hours
∆∆ CPM = malnourished alcoholics
What is the clinical presentaiton of Central Pontine Myelinolysis?
quadriplegia, dysarthria, dysphgia, seizures, coma, death
How is SIADH treated?
Demeclocycline
* Reduces responsiveness of collecting tubule cells to ADH
* Monitor U&Es (risk of nephrotoxicity)
Tolvaptan
* V2 receptor antagonist
What is pseudo-hyponatraemia?
How can you differentiate between pseudo- and true hyponatraemia?
Even though on lab results patients has hyponatrameia, pt is not truely hyponatreamia
**Indicator: Serum osmolality **
If Low = true hyponatraemia
IF Normal or high: psuedo-hyponatraemia
What are some of the causes of psedo-hyponatraemia?
- Pseudo: lab analysis mistake that mistakes increased plasma protein or lipid as water/plasmy –> underestimation of sodium
Other cuases
1. High osmolality (e.g. mannitol, glucose) –> attracts more water –> higher diluation of sodium
What are the causes of hypernatreamia?
Unreplaced water loss
* Gastrointestinal losses, sweat losses
* Renal losses: osmotic diuresis (diabetes) , reduced ADH release/action (Diabetes insipidus)
Patient cannot control drinking –> dehydration
* e.g. children, elderly
What invetigations should be done in a patient with suspected diabetes insipidus?
- Serum glucose (exclude diabetes mellitus)
- Serum potassium (exclude hypokalaemia)
- Serum calcium (exclude hypercalcaemia)
- Plasma & urine osmolality (plasma = high, urine = low)
**Water deprivation test (diagnostic test) ** –> urine does not get concentrated)
How should Hypernatraemia be treated?
- Fluid replacement with 5% dextrose (initially)
- Treat underlying cause
How should diabetes insipidus be treated?
- Cranial: Desmopressin
Nephrogenic: thiazide diuretics (bizarre but works)
How do you differentiate between cranial and nephrogenic diabetes insipidus?
- Measure urine osmolality after water deprivation test with administration of desmopressin
Cranial = osmolality will increase
Nephrogenic = osmolality will not increase
