Flashcards in Small Group 1 Electrolyte Balance Deck (11):
1. Calculate or estimate GFR using Cockroft-Gault, MDRD and urine clearance.
CG: CC= [(14- age) x lean weight Kg]/ [serum creatinine mg/dL x 72] most accurate at higher GFRs
most widely used is MDRD used to define stages of CKD-- gives estimated GFR and will be most accurate for patients GFR<40mL/min
CKD-EPI most accurate for both low and high GFRs
creatinine clearance U x V/P x t (overestimates GFR)
2. Explain the use and limitations of methods for assessing GFR.
creatinine clearance overestimates GFR
CG is most accurate at higher GFRs
MDRD is most accurate at low GFRs <40 mL/min
3. Describe the distribution of fluid and electrolytes in body compartments and explain how these change in diseases states.
50% of TBWt in women and 60% TBWt in men is the water content
two thirds TBW, ⅔ is ICF, ⅓ is ECF, of the ECF, ¼ is intravascular (5% TBWt) ¾ is interstitial
if there is no change in the plasma osmolality, there is no change ICF volume
4. Clinically differentiate abnormalities in ECF sodium content from abnormalities in serum sodium concentration (abnormalities in water balance).
orthostatic BP and rapid pulse represent decreased ECF volume/sodium content
when trying to replace intravascular volume, best to use normal saline solution
What is the relationship between serum creatinine and GFR?
inverse parabolic relationship, greater changes in serum creatinine for first decreases in GFR
What is the action of carbonic anhydrase inhibitors like acetazolamide?
blocks the sodium-hydrogen exchange, and can serve as a potent diuretic since 70% of sodium is reabsorbed in the proximal tubules-- it also causes the patient to loose bicarbonate and become academic
Agents can reduce Na and K or H exchange by blocking aldosterone (name these drugs) or apical sodium channel (name these drugs)
aldosterone: spironolactone, eplerinone
apical sodium channel: amiloride, triamterene
How do you calculate what the serum osmolality should be?
2 x serum Na + serum glucose/18 + BUN/2.8
What do you assume about the osmolality of patient that is unconscious and not supplemented with IV fluids?
serum osmolality will be high, fluid losses will be hypotonic
in this case water is loss from both body compartments (proportionally)
note plasma volume is well preserved because total NaCl has not decreased much
good to treat with free water or D5W since sodium is normal
Why would a patient with ADH deficiency be able to maintain normal serum osmolality? What is the medullary gradient changed without ADH?
patient is able to drink and would likely drink lots of hypnotic fluids such as water
without ADH, medullar gradient is washed out by high tubular flow rates