Flashcards in Fluid-Electrolyte Balance and Disturbances Deck (13):
_________ controls threshold.
A _______ in plasma calcium concentration leads to an increase in nerve and muscle excitability because the threshold shifts towards the resting potential.
______ % of Calcium are in bones/teeth, the _____ % that is called ionized calcium is what controls all of the threshold potentials.
Can s\s of hypocalcemia be elicited when the patient hyperventilates?
Yes. hyperventilation causes a resp alkalosis. Ionized calcium decreases, thus eliciting s\s of hypocalcemia.
Name in order of the fastest to slowest for treatment of hyperkalemia. (7)
1) give Ca++ (fastest, but does not correct the K+); only takes 1-2 min
2) administer HCO3-; takes 3-5 min; HCO3- decreases H+ concentration in plasma (metabolic alkalosis)--> H+ shifts out of cells to buffer alkalosis, and in exchange K+ shifts into cells
3) hyperventilate; 10-15 min; H+ concentration in plasma decreases (resp alkalosis)--> H+ shifts out to buffer the alkalosis in exchange for K+
4) give insulin-glucose--> insulin stimulates Na-K+ pump, driving K+ into cells; insulin also opens glucose channels; glucose is given with insulin to prevent hypoglycemia; ~30 min to work
5) administer a B2-agonist (stimulates Na-K pump); ~30 min to work
6) Give Kayexalate; min--> hours--> days
7) Dialyze patient--> min--> hours--> days
*loop diuretics take approx... 25-45 min to work
For each _____mmHg decrease in PaCO2, serum K+ decreases ______ mEq/L.
Normal RMP for nerve cells is _____mV.
Normal RMP for muscle cells is _____mV.
Normal threshold for muscle cells is _____mV.
Cardioplegia solution used during CABG surgery has a high concentration of _____, and the cardiac cells depolarize to a level between threshold and 0mV.
K+; action potential is elicited and contraction occurs--> after that there is no electrical activity and Na+ gates are shut in inactivated state until normal K+ is restored
Why are PVCs seen with hypokalemia?
hypokalemia leads to a decrease in excitability d\t hyperpolarization of the SA and AV node--> but there are ventricular Purkinje fibers that more readily depolarize to threshold and PVCs occur
How does hyperventilation lead to the lowering of ionized calcium?
Both H+ and Ca+ bind to plasma proteins-> hyperventilation lowers H+ concentration causing protein to release H+ (law of mass action), thus freeing up Prot- which can then bind ionized calcium and correspondingly lower plasma concentration of ionized calcium