[5] Hyponatraemia Flashcards
What is acute hyponatraemia?
A sudden drop in the blood sodium levels
What is the most common post-operative electrolyte imbalance?
Obviously hyponatraemia else why would it be in this deck lol
What is the normal range for sodium?
135-145mEq/L
What is hyponatramia classified as?
Below 135mEq/L
What functions in the body is sodium essential for?
- Maintaining BP
- Supporting function of muscles and nerves
- Fluid balance regulation
How is sodium important in fluid balance regulation?
It is a large contributor to plasma osmolality (more sodium = higher osmolality)
What effect does a low plasma osmolality have on water movement?
It causes water to move intracellularly
What can low plasma osmolality in the brain cause?
Cerebral oedema and raised intra-cranial pressure
What is the clinical relevance of the effect of low plasma osmolality on the brain?
Profound hyponatraemia can result in cerebral dysfunction
Why are the effects of sodium on tissue osmolality important post-operatively?
Because low serum can result in significant tissue oedema that can impair tissue healing. This can be particularly troublesome in surgical wounds or anastomoses
Why is hyponatraemia common after surgery?
- Fluid retention is seen as part of the stress response to surgery
- Surgical patients recieve significant volumes of intravenous fluid during the perioperative fluid
Why is fluid retention seen as part of the stress response to surgery?
The stress response causes an increase in hypothalamic-pituitary secretion, resulting in increased cortisol and ADH release.
How does the stress response causing fluid retention after surgery cause hyponatraemia?
Because the free water reabsorption that is stimulated is in excess to the sodium reabsorbed
More water than sodium, dilutes it
What kind of IV fluid can cause hyponatraemia?
Dextrose, especially if use is prolonged or excessive
How does dextrose IV fluid cause hyponatraemia?
It has a diluational effect on the body’s serum sodium levels
What are the causes of hyponatraemia?
- Some medications
- Congestive heart failure, and other diseases affecting heart, kidneys, and liver
- SIADH (syndrome of inappropriate anti-diuretic hormone)
- Severe vomiting or diarrhoea
- Excessive hydration
- Dehydration
- Adrenal glad insufficiency, e.g. Addisons disease
- Ecstasy
What medications can cause hyponatraemia?
- Diuretics
- Anti-depressants
- Pain medications
What are the symptoms of hyponatraemia?
Mild hyponatraemia is asymptomatic
- Nausea and vomiting
- Headache
- Confusion
- Loss of energy and fatigue
- Restlessness and irritability
- Muscle weakness, spasms, or cramps
- Seizures
- Coma
How is hyponatraemia investigated?
- Paired serum and spot urine for U&E and osmolality
- Plasma glucose
- If suspicion of adrenal insufficiency or severe hypothyroidism, check serum cortisol and do thyroid function tests.
How is hyponatraemia managed?
- Careful fluid balance
- Cessation of drugs that may contribute to hyponatraemia
- Treat underlying cause if possible
How should careful fluid balance be obtained in hyponatraemia?
- Close monitoring of fluids, catheterising if neccessary
- IV fluids are generally advised over enteral hydration
What IV fluids should be given in hyponatraemia?
0.9% sodium chloride, or Hartmann’s
Why are IV fluids generally advised over enteral hydration in hyponatraemia?
Because they provide greater control to serum electrolyte levels
What should be monitored regularly during hyponatraemia management?
Renal function and electrolyte levels
