Disorder of Salt and water balance- CIS Flashcards
Commonly patients who develop hyponatremia typically have an impairment in renal water excretion, most often due to inability to suppress _?
ADH
What is pseudohyponatremia and what are some lab findings with pseudohyponatremia?
Pseudohyponatremia is errors in lab measurement of Na. You’ll commonly also see hyperproteinemia, hyperlipidemia, hypercholesterolemia along with hyponatremia.
What can hyperglycemia and unmeasured osmol do to your Na level?
Leads to hyponatremia.
What are some findings you’d commonly see with true hyponatremia?
- dilute urine, low ADH
2. Concentrated urine, high ADH
What are some diseased conditions where you’d see concentrated urine with high ADH leading to hyponatremia?
- CHF (decreased effective circulating volume)
2. SIADH
What are some conditions where you’d see dilute urine with low ADH leading to hyponatremia?
- pscyhogenic polydipsia,
2. Pregnancy (reset of osmostat)
Why might you see neurological problem with patients with rapid onset of hyponatremia?
Cells can swell due to H20 movement into cells including neural cells in the brain.
How do you calculate osmolar gap?
Osmolar gap is the difference between plasma osmolality and measured osmolality. Osmolar gap = (2x Na) + (glu/18) + (BUN/2.8)
What is normal level of osmolar gap?
Less then 10
What does it mean when a patient has an osmolar gap greater than 10?
It means there’s something else in the plasma that’s adding to the osmolarity that hasn’t been accounted for. For example, pt who ingests antifreeze.
What two things needs to be below normal in order for it to be considered true hyponatremia?
Plasma Na concentration and osmolality.
How can you tell if a pt was compensating for hyponatremia?
Urine should be dilute and high volume. Pt should have circulating ANP at low levels.
What diseased condition can lead to high plasma osmolality and high ADH secretion?
Dehydration, or central DI.
In Dehydration what would be the Uosm and Posm ratio? what about in central DI?
Dehydration >1
Central DI
If both plasma osmolarity is low and plasma ADH level is low, what clinical condition is likely?
Primary polydipsia.
In primary polydipsia what is Usom and Posm ratio?
By looking at patient’s hx and chemistry, how can you tell if a patient’s hyponatremia is due to primary polydipsia?
- Hx of polydipsia
- Previous diagnosis of Schizo
- Na, osmolarity measurements (should be low)
What condition can cause low osmolarity but high ADH?
SIADH
What disease can cause SIADH?
- Small cell carcinoma.
2. adrenal cortex tumors.
How can you differentiate whether a patient’s hypernatremia is nephrogenic or central?
Patients with DI will excrete dilute urine and retain excess salt causing increased osmolarity. You can test to see if the patient is lacking ADH (the brain isnt’ making enough) or if the kidney just isn’t responding to ADH. You would give patients synthetic ADH and see if their urine concentration is increased. If it’s increased then it’s central (the body wans’t making enough), and if it’s not fixed and it’s probably nephrogenic.
What is the water deprivation test?
DI patients with hypernatremia and dilute urine, water deprivation test is used to see if ADH is working properly. Patient is derpived of water consumption and an urine sample is taken 6-8 hours later. If urine is dilute compared to baseline then it’s a nephrogenic problem because the kidney isn’t respondign to ADH.
In a patient with nephrogenic DI, how would osmolarity change with administration of desmopresin?
Urine osmolarity would not change. Urine desmopresin levels would increase, since the patient isn’t able to use it up.
During extrarenal water loss (excessive sweating, fever, diarrhea, vomitting) is urine output decreased or increased? is plasma ADH decreased or increased?
Urine output is decreased. ADH is increased.
A patient who is on lithium supplements as a treatment for a psychiatric disorder, presents with hypernatremia? what’s causing this hypernatremia?
Patient’s ADH isn’t working because Li limits the ability of V2 receptors to generate cAMP and decreasess the biologic activity of ADH. the Body is unable to retain water w/o ADH and thus presents with hypernatremia.
