Lab Evaluation of Electrolytes and Fluids Flashcards
What is measured osmolality?
Measured osmolality is looking at the measurement of solute by freezing and/or vapor-point eval
What are the formulas for calculated osmolality?
Serum - 2[Na+] + (gluc/18) + (urea/2.8) = normally 299.4osm
Plasma - 1.86[Na+ + K+] + gluc + urea = normally 290-310 in dogs and 308-335 in cats
urine - equates closely with USG; normally 50-2800 in dogs and 50-3000 in cats
What is the difference btwn measured and calculated osmolality?
Osmolar Gap
What does an increase in the Osmolar Gap mean?
Increased osmolar gap = presence of exogenous solutes or pseudohyponatremia
How is osmolality of extracellular fluid regulated?
by adjusting water balance
How is the volume of extracellular fluid regulated?
by changes in [Na+]
-influenced by changes in vascular pressure
What are the clinical signs associated with water imbalance?
changes in skin turgor, CRT and changes in body weight
What are the biochemical signs associated with water imbalance?
an increase in PCV and plasma protein and/or BUN = dehydration
What does Aldosterone cause? When is it secreted?
an increase in Na+ (and H2O) and Cl- reabsorption and increased K+ excretion through distal tubules
Aldosterone is secreted in response to angiotensin, ACTH and hyperkalemia
What are the 3 types of dehydration?
hypertonic
isotonic
hypotonic
hypertonic dehydration means…
water loss > electrolyte loss
Increased serum Na and Cl
water is moved from ICF to ECF to maintain volume
isotonic dehydration means…
water loss = electrolyte loss
serum Na and Cl don’t change
no water shift btwn ICF and ECF - - there will be a decreased in ECF vol.
hypotonic dehydration means…
water loss
What electrolytes are we concerned with in our Labs?
Na
Cl
K
Most abnormalities in serum [Na+] are due to abnormalities in….
water
What can cause hyponatremia?
excess Na loss: V, D, renal loss, sweating, severe burns
increased extracellular water:
-osmotic shift from ICF to ECF - - hyperglycemia or mannitol admin.
-hypervolemia – decr. Na –> impaired H2O excretion –> fluid retention –> dilute Na
-syndrome of inappropriate ADH secretion (SIADH):
excess ADH despite lack of normal stimuli and normal renal function - - neoplasia and CNS/pulmonary disease
What is 3rd space syndrome?
extracellular Na/K equilibrates in sequestered fluids
- hyponatremia
- hypokalemia
What are CS’s of hypernatremia?
neurologic, lethargy, depression, altered mentation, V, seizures
How does the CNS adapt to hypernatremia in chronic hyperosmolar states?
producing idiogenic osmoles….
What happens when the CNS correct the hypernatremia faster than the idiogenic osmoses can be cleared?
cellular swelling leading to cerebral edema, convulsions and death
What causes hypernatremia?
inadequate water intake - primary hypodypsia due to defective ADH osmoregulation
excess water loss/deficit - diabetes insidious, panting, fever, urinary loss, osmotic diuresis, and GI shift of water
excess Na intake/retention - Increased ADH
What is the function of Cl-?
transport of important electrolytes in water, crosses membranes by active transport, and acts as a conjugate anion in acid-base metabolism
What are the CS’s associtated w/ hypochloremia?
neuro signs probably due to metabolic alkalosis and decreased ionized Ca2+
What causes hypochloremia?
Cl- loss = Na+ loss –> same causes of hyponatremia
Cl-loss > Na+ loss
- decreased Cl- = increased HCO3- = metabolic alkalosis
- loss/sequestration of Cl- (cattle)
- aggressive diuretics like thiazides
