Miscellaneous - Electrolytes

Question 1

Findings of hyperkalemia on EKG?

Answer 1

Peaked T waves with sinus rhythm

K+ above 8 -> absent P waves with marked prolongation of the QRS complex which merges with the T-wave to form the classic sine-wave pattern

May progress to Vfib/aystole

Question 2

Treatment options for hyperkalemia?

Answer 2

1. 10% calcium gluconate - stabilizes the cardiac membranes (10-20 mL, second dose if no response at 5-10 minutes) - lasts 30-60 minutes
2. IV serum bicarbonate - shifts K into the cells - (50 mEq bolus IV over 5-10 minutes) - lasts ~2 hours
3. IV insulin - stimulates cellular potassium uptake (given with glucose) - (10 U insulin + 100 mL 50% glucose) - lasts up to 4 hours
4. Loop and thiazide diuretics - increase K excretion
5. Kayexalate - promotes exchange of potassium for sodium along the GI tract
6. Patiromer and Zirconium - bind K in the GI tract

Question 3

Causes of hyperkalemia in CKD?

Answer 3

• Decreased nephron mass and impaired renal K excretion
• Meds interfere with aldosterone production
• Excessive potassium intake
• Transcellular shifts of potassium
• Pseudohyperkalemia (hemolyzed specimen, high WBC/platelet count)
• Metabolic acidosis
• Hyperglycemia, insulin deficiency, inorganic metabolic acidosis can shift K out of intracellular location

Question 4

Causes of hypocalcemia in CKD?

Answer 4

Failure of final step of 25-Vitamin D activation (1-hydroxylation), which occurs in the kidney

Decreased active Vitamin D -> decreased intestinal Ca2+ absorption -> PTH stimulated to try to correct hypocalcemia

Question 5

Signs and symptoms of hypocalcemia?

Answer 5

Increased excitability of neuromuscular cells leads to perioral paresthesias, twitching, spasms, seziures

Question 6

What is Chvostek sign?

Answer 6

Contraction of the facial muscle when the facial nerve is tapped

Question 7

What is Trousseau’s sign?

Answer 7

Carpal spasm when the brachial artery is occluded by a BP cuff

Question 8

Signs/symptoms of hypernatremia?

Answer 8

Lethargy, weakness, irritability
Progresses to delirium, encephalopathy, seizures
Note that elderly patients often have few signs/symptoms until concentration reaches 160

Question 9

Three major categories of hypernatremia?

Answer 9

1. Pure water loss
2. Hypotonic fluid loss
3. Hypertonic sodium gain

Question 10

Causes of pure water loss?

Answer 10

Decreased water intake
Diabetes insipidus

Loss of equal percentage of volume

Question 11

Causes of hypotonic fluid loss?

Answer 11

Diuretics
Osmotic diuresis
GI losses (vomiting, diarrhea, NG tube output)
Burns
Sweating

Loss of extracellular volume

Question 12

Causes of hypertonic sodium gain?

Answer 12

Iatrogenic sodium bicarbonate infusion

Ingestion of sodium solutions

Question 13

Who are at highest risk of hypernatremia?

Answer 13

Lack of access to water

Physically unable to drink water (dementia, AMS, infants, elderly, untbation)

Question 14

Estimated serum osmolality?

Answer 14

= 2(Na) + glucose/18 + BUN/2.8

Question 15

Rx patients with hypernatremia?

Answer 15

If dehydration with volume depletion, give IV NS to correct the depletion.

Once clinically euvolemic, patient needs hypotonic solution to lower the serum sodium:

• Calculate TBW
• Calculate effect of 1L of selected fluid on current serum Na
• Divide ths into the total amount Na desired to be lowered over 24 hours
• Account for obligatory 24 hour water loss (~1.5 L)
• Convert to mL and divide by 24 for rate/hour

Question 16

How is cerebral edema prevented when correcting hypernatremia?

Answer 16

Lower the serum sodium by only 10-12 mEq/L per day

Question 17

List hypotonic solutions

Answer 17

1. D5W = 0 mEq Na/L
2. 0.2% NS in D5W = 34 mEq Na/L
3. 0.45% NS in water = 77 mEq Na/L

Question 18

Total body water = ?

Answer 18

%water * weight kg

% water in males = 0.6, females = 0.5

Question 19

Change in serum Na?

Answer 19

= (Infusate sodium - serum sodium)/(TBW + 1L)

Question 20

Describe fluid compartments of the body

Answer 20

2/3 intracellular

1/3 extracellular -> 1/4 intravascular, 3/4 interstitial