Control of ECF and Osmolality Flashcards
Hyponatremia
Pna<135 typically due to water retention
3 types of hyponatremia
psuedonatremia, isotonic or hypertonic hyponatremia, and Hypotonic hyponatremia
What is psuedonatremia?
Artifactual reading due to a measurement problem, generally due to hyperlipidemia or hyperproteinemia
What is Isotonc or hypertonic hyponatremia?
the presence of unmeasured effective osmoles (mannitol) is causing the shift of H2O from ICF to ECF (hyperglycemia, contrast)
What is Hypotonic hyponatremia?
Effective osmolality of the plasma is LOW, TRUE hyponatremia
Hypotonic hyponatremia has 3 classes
Hypovolemic (volume depletion, low BP), Euvolemic, and Hypervolemic (ECF volume expansion, edema)
Hyponatremia is secondary to
defect in renal water clearance (since low Posm, low ADH, high H2O excretion)
Reasons for defect in renal water clearance?
Excessive water drinking (psychiatric issue) usually due to medications
Psuedohyponatremia
Na levels appear high when measured in total plasma, but normal when measured in plasma water
Isotonic or Hypertonic Hyponatremia causes
presence of effective osmole
Syndrome of Inappropriate ADH (SIADH)
euvolemia; plasma ADH is inappropriately HIGH; presistant ADH and persistant reabsorption of H2O
Tricyclic antidepressants and morphine can cause SIADH
stimulate ADH and can cause hyponatremia
Presentation of patient with SIADH
hyponatremia, (-) free water clearance, despite need to excrete
Treatment for SIADH hyponatremia
H2O restriction, blockade of ADH at the collecting duct
Nephrogenic Syndrome of Inappropriate Antidiuresis
SIADH like symptoms described by a GAIN OF FUNCTION of the ADH receptors (V2)
Exertion and Hyponatremia
prolonged exercise (>4hr) loss of electrolytes through sweat and excessive intake of HYPOTONIC fluids, ALSO during exercise ADH is inappropriately secreted
Hypernatremia
pna >145, often the result of unreplaced water loss
Body’s defense against hypernatremia
ADH and thirst
Diabetes insepidus
excretion of large volumes of HYPOTONIC urine due to a defect in ADH (inability to resorb water properly)
Central diabetes insepidus
decreased production of ADH from pituitary (stroke, tumor, drug-induced, genetic)
Nephrogenic Diabetes insepidus
kidneys inability to respond to ADH (drug-induced [LITHIUM] or defect in V2 receptor)
In a normal patient, water deprivation will result in
ADH secretion, water retention, and concentrated urine
In a patient with Central DI, water deprivation will result it
no ADH, water still lost, Uosm will remain < Posm
Central DI, patient when given endogenous ADH
ADH, will cause water retention, and urine concentration