Sodium and Fluid balance Flashcards
What is Osmolality and what is the Normal Osmolality of blood?
Osmolality is the number of solute particles in 1kg of Solvent
-> Normal Range is 275-295mOsmol/kg
Where is AHD released from and what are its 2 actions?
ADH - Anti-Diuretic Hormone, is released by the posterior pituitary
V1 (Vasopressin)
-> Acts on vascular smooth muscle and mediates vasoconstriction
V2
- > Acts on the collecting duct cells on the Kidney
- > Promotes water retention by inserting Aquaporin-2 channels
What Stimulates ADH release?
i) Baroreceptors
- > found in the carotids, atria and aorta
- > identify when there is a low blood volume/pressure
- > Stimulate ADH release
ii) Osmoreceptos
- > found in the hypothalamus
- > identify when the osmalality rises
- > Stimulate ADH release and thirst
What is hyponatraemia? How can it be identified and what is true hyponatraemia?
Hyponatraemia is when sodium is below 135mEq/L
It is the commonest electrolyte imbalance in hospitalised patients.
This can be identified by doing a set of U&Es
True Hyponatraemia is when Serum Osmalality is also LOW.
i.e. below 275mOsmol/kg
What are Signs of Low Volume Status?
-> Tachycardia
-> Postural Hypotension
-> Dry mucous membranes
-> Reduced Skin Turgor
-> Reduced Urine Output
-> Drowsy/Confused*
This may be a sign of severe hyponatraemia, ESCALATE.
-> Low urine Na+(<20)
What is the most reliable indicator of a hypovolaemic state?
Urine Na+ < 20 is MOST reliable of a hypovolaemic state*
- > i.e. the patient is holding onto their salt in an attempt to retain their fluid
- Not a useful marker if the patient is on diuretics
What are signs of high volume status?
- > Raised JVP 6-8cm.
- > Bibasal Crackles
- > Peripheral Oedema
What are causes of Hypovolaemic Hyponatraemia?
- Renal – raised urinary sodium;
- > Diuretic Use
- > Salt Losing Nephropathy - Extra-Renal – low urinary sodium;
- > D&V
What are investigations for Hypovolaemic Hyponatraemia?
Investigations
- > Volume Status
- > Urine Sodium, if > 20 – Renal Cause
What is the management for Hypovolaemic Hyponatraemia?
Management
-> Slow volume replacement with 0.9% Saline
What are causes of Euvolaemic Hyponatraemia?
Causes
- > Adrenal Insufficiency
- > Hypothyroidism
- > SIADH;
What are investigations for Euvolaemic Hyponatraemia?
Investigations
- > TFT’s
- > SST (Short Synacthen Test)
- > Plasma and Urine Osmalality *
SIADH
PLASMA = LOW, URINE(>100) = HIGH.
What is the management for Euvolaemic Hyponatraemia?
Management
- > Fluid Restrict
- > Treat the underlying cause
What is the first step in the clinical assessment of a patient with hyponatraemia/
Clinical Assessment of volume status
How dies D&V cause excess water in hypovolaemic hyponatraemia?
- Lose BOTH water and sodium from D&V
- Baroreceptors detect loss of volume and stimulate ADH
- ADH leads to increased water reabsoprtion, not sodium.
- Still less water than before (hypovolaemic) and less salt in proportion (hyponatraemic).
What are causes of SIADH?
i) CNSi.e. Tumours, bleeds, trauma
ii) Lung pathology i.e. Small Cell Lung Cancer, PE, Pneumothorax, Pneumonnia
iii) Drugs i.e. SSRI, TCA, Opiates, PPI’s, Carbamazepine
iv) Tumours
v) Surgery
Brains, lungs and drugs
What are the steps to reach a conclusion of SIADH?
- No hypovolaemia
- No hypothyroidism
- No adrenal insufficiency
- Reduced plasma osmolality
- Increased urine osmolality (>100)
What are causes of Hypervolaemic Hyponatraemia?
Causes
- > Cardiac Failure
- > Cirrhosis
- > Renal Failure
What are the investigations for Hypervolaemic Hyponatraemia?
Investigations
?Hypervolaemic Clinical Signs
What is the treatment for Hypervolaemic Hyponatraemia?
Treatment
- > Fluid Restriction
- > Treat the cause
What are signs of Severe Hyponatraemia and how do you manage this?
Reduced GCS, Seizures,
Seek Expert Help
-> Hypertonic 3% Saline
How does hypothyroidism cause hyponatraemia?
- Decreased TFT’s lead to decreased contractility of the heart.
- Decreased blood pressure as a result detected by baroreceptors
- Lead to ADH release and water reabsorption but not sodium
What is the most important point to remember while correcting hyponatraemia?
- Serum Na must not be corrected >8-10 mmol/L in the first 24hrs
- Risk of osmotic demyelination/Central Pontine Myelinolysis (quadriplegia, dysarthria, dysphagia, seizures, coma, death)
What are the drugs used to treat SIADH?
If water restriction is insufficient:
- Demeclocycline (Reduce response to ADH)
- Tolvaptan (V2 Receptor Antagonist)
Fluid Restriction + Salt Tablets + Furesomide
