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10 Cards in this Set
- Front
- Back
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What medications commonly cause hyponatraemia
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thiazide diuretics - typically within first 2 weeks of initiation
SSRIs - stimulate ADH release NSAIDs - potentiate the effect of ADH |
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What is the normal range of plasma osmolality? Does a low osmolality imply that the plasma is more dilute or concentrated?
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275-295 msom/kg H2O
low osmolality implies the plasma is more dilute |
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What are the two most important values to consider when differentiating the causes of hyponatraemia? How will the results of these investigations guide your thinking
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plasma OSMOLALITY - if it is normal it implies pseudohyponatraemia or hyperglycaemia
if it is low, the urine osmolalitly must be checked. if the urine osmolality is low (<100) it suggests primary ploydipsia as the cause. If the urine osmolality is inappropriately high (>200) the causes must be distinguished based on the fluid status of the patient. |
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What are the common causes of pseudohypernatremia?
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hyperglobulinemia and hypertriglyceridemia
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What is the mechanism of hyponatraemia in hyperglycemia
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hyperglycaemia draws water from the cells into the ECF diluting the sodium concentration
increased tonicity also stimulate thirst and ADH secretion which contribute to H2O retention |
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following neurosurgical procedures what two causes of hyponatraemia need to be considered?
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SIADH
Cerebral salt wasting |
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How is SIADH distinguished from cerebral salt wasting
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both have hyponatraemia with a low plasma osmolality and an increased urine osmolality.
SIADH is associated with euvolemia or slight volume expansion - ADH mediated H2O retention - wheres as cerebral salt wasting is associated with hypovolemia - kidney wasting salt SIADH is more common than CSW. CSW associated with SAH |
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What is it important to make the distinction between SIADH and CSW
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treatments differ
SIADH - fluid restrict CSW - IVT with normal saline |
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what is the risk of correcting hyponatraemia to quickly
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cell shrinkage may occur and can precipitate osmotic demyelination
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What are the causes of hypernatraemia
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hypovolaemiac - dehydration (GI losses), diuretics (frusemide), osmotic diuresis (hyperglycaemia, mannitol, relief of acute obstruction)
Euvolaemic - diabetes insipidus Hypervolaemic - iatrogenic - saline, hyperaldosteronism |
