Hypernatremia Flashcards
What is hypernatremia?
Serum sodium concentration of >145 mmol/L (normal serum sodium concentration is in the range of 135-145 mmol/L).
What is serious hypernatremia?
Plasma sodium concentration of >158 mmol/L (158 mEq/L); may present with serious signs and symptoms, such as hyperthermia, delirium, seizures, and coma, prompting more urgent treatment of the condition.
What are 3 different pathological causes of hypernatremia?
- Excess water loss
- Excess hypertonic fluid
- Decreased thirst
What are the signs of hypernatremia?
- CNS manifestations→ lethargy, weakness and irritability
- Orthostatic hypotension
- Decreased JVP
- Signs of hypovolaemia→ tachycardia and dry mucous membranes
What are the symptoms of hypernatremia?
- Diarrhoea and vomiting
- Impaired thrist
- Weight loss
- Oliguria
Why does hypernatremia cause CNS manifestations?
If hypernatraemia is acute, the higher osmolality in the extracellular space causes water to move out of brain cells causing the brain to shrink. This shrinkage can lead to neurological consequences, including lethargy, weakness, and irritability.
Severe manifestations can include intracranial haemorrhage, seizures, stupor, coma, and death.
What investigations should be ordered for hypernatremia?
- Serum electrolyte panel with glucose, urea and creatinine
- Urine osmolality
- Serum osmolality
Why investigate serum electrolyte panel with glucose, urea and creatinine?
Should be ordered in all patients with suspected hypernatraemia.
Serum sodium >145 mmol/L and other parameters variable.
Why investigate urine osmolality?
Should be ordered in all patients with hypernatraemia as it may help determine the underlying aetiology.
Aetiology:
- <150 mmol/kg diabetes insipidus
- 200-500 mmol/kg renal concentrating defect
- >500 mmol/kg pure volume depletion
Why investigate serum osmolality?
Hypernatraemia is always associated with serum hyperosmolality (>295 mmol/kg).
Briefly describe the treatment for hypernatremia
Treatment should be directed at addressing the underlying cause (e.g., stop offending medication, treat fever, relieve urinary obstruction, give insulin, discontinue sodium sources), as well as replacing any free water deficit and ongoing fluid losses, while monitoring serum sodium concentration to ensure levels are returning to the correct range at the desired rate.
Describe the 4 steps in treating hypernatremia
- Calculating the free water deficit
- Determining a suitable serum sodium correction rate
- Estimating ongoing free water losses (if applicable)
- Designing a suitable fluid repletion program that takes into account the estimated free water deficit, the desired serum sodium correction rate and any ongoing free water losses
What is the first-line treatment for hypernatremia regardless of type (e.g. free water losses, inadequate free water intake or accidental/ iatrogenic excess intake os sodium)?
Oral or IV fluid replacement.
What is the fluid of choice in treating hypernatremia?
Water administration via the oral (or nasogastrical route) is preferred, if possible. If not, intravenous administration is required.
Dextrose 5% in water is recommended.
Which IV fluids shoud be avoided in patients with hypernatremia?
Intravenous fluids containing sodium (which includes saline and lactated Ringer’s solution) should be avoided in these patients unless they are severely hypotensive or in shock.
