Fluids and Electrolytes

Question 1

How is TBW distributed in humans?

Answer 1

2/3 goes inside the cell
1/3 goes outside of the cell:
1/4 to vasculature, 3/4 to interstitial fluid

Question 2

Difference between 5 and 25% albumin?

Answer 2

5% is isotonic and iso-oncotic (water goes to vasculature)

25% is isotonic and hyper-oncotic (goes to vasculature AND pulls water to vasculature from interstitial space)

Question 3

In what disease states is albumin administration inappropriate?

Answer 3

Malnutrition
Cirrhosis (exception: paracentesis, whatever that is)

Question 4

What is the fluid requirement in adults?

Answer 4

1.5 L/day for the first 20 kg
then 20 mL/kg for each additional kg

INITIAL FLUID BOLUS in septic shock: 30 mL/kg

Question 5

How does D5 distribute?

Answer 5

D5 is free water, so it distributes the same as TBW

2/3 to Cell
1/3 to extracellular space
1/4 to vasculature, 3/4 to interstitial space

Question 6

How does 0.9% NS distribute?

Answer 6

NS = normal saline, sodium pump keeps sodium OUT of the cell so it ALL goes extracellular.
3/4 interstitial
1/4 vasculature

Question 7

How does 0.45% NS distribute?

Answer 7

Half free water, so 1/3 goes into the cell!
The NS stays OUT of the cell bc of the sodium pump

so 1/3 to cell
2/3 to extracellular space
1/4 to vasculature, 3/4 to interstitial fluid

Question 8

When is 0.45% NS used?

Answer 8

Often used as maintenance IV fluid in patients with hypernatremia

Question 9

How does 5% albumin distribute?

Answer 9

Basically all of it stays in the vasculature because albumin is too big to cross the membranes

USED TO REPLETE VASCULAR VOLUME

Question 10

How does 25% albumin distribute?

Answer 10

All stays in the vasculature bc albumin is too big to cross membranes, but it also pulls water from the interstitial space bc 25% albumin has a hyperoncotic pressure

Question 11

When is 25% albumin used?

Answer 11

Often used in interstitial and pulmonary edema (bc it pulls water!)

Its use is followed by a loop diuretic

Question 12

Which solutions can cause phlebitis?

Answer 12

Solutions that are more than 900 mOsm/L

Sodium chloride 3%

Question 13

Which solutions can cause hemolysis?

Answer 13

Solutions that are less than 154 mOsm/L

Sterile water
Sodium chloride 0.225%

Question 14

How to calculate osmol gap?

Answer 14

Osm of serum - Osm calc

Calculated osmoles: 2Na + Glu/18 + BUN/2.8

Question 15

What electrolytes are normally found in the ICF?

Answer 15

Potassium (3.5-5 mEq/L)
Magnesium (1.5-2.8 mg/dL)
Phosphorous (2.7-4.5 mg/dL)

Question 16

What electrolytes are normally found in the ECF?

Answer 16

Sodium (135-145 mmol/L)
Chloride (98-107 mmol/L)
Bicarb (24 mmol/L)

Question 17

What is the treatment goal for hypokalemia?

Answer 17

4.0 mEq/L

Question 18

How to treat hypokalemia?

Answer 18

First check Mg and adjust that first
Check ECG if K is less than 3.0 mEq/L

Use oral preferably, 20-80 mEq/day
IV 10-20 mEq/day, 20 requires central line

Question 19

What should you do when a pt has high potassium?

Answer 19

Make sure it’s not a hemolyzed sample before treating

Question 20

How do you treat hyperkalemia if it’s really high?

Answer 20

Stabilize cardiac membranes from effect of potassium (calcium chloride preferred for central line, calcium gluconate OK for peripheral access)

Shift K+ intracellularly with insulin (unless hyperglycemia is present)
or
with sodium bicarbonate (reverses H+/K+ ATP-ase activity)
or
B-2 agonist (increases Na+/K+ ATPase activity)

Question 21

How do you treat hyperkalemia that is less than 6.5 mEq/L?

Answer 21

This is low so just remove K+ using sodium polystyrene (exchanges 1mEq/g in the large intestine)
Loop diuretics increase renal K+ excretion
Dialysis (esp if renal failure)

These take a while!!

Question 22

How do you treat chronic hyperkalemia?

Answer 22

Patiromer
Non-absorbed cationic exchange polymer binds K+ in the GI tract
BINDS A LOT OF DRUGS - GIVE 6 HRS BEFORE OR AFTER ANYTHING ELSE

Question 23

What is the treatment goal for hypomagnesemia?

Answer 23

Goal is over 2.0 mg/dL in hospitalized pts
Give Mg sulfate 1-2 g over 1 hour
Oral can give magnesium oxide 800-1600 mg/day*

*Note: Diarrhea/nausea common, and watch out for drug interactions with tetracyclines, fluoroquinones

Question 24

What is the treatment for hypermagnesemia?

Answer 24

Supportive (Discontinue Mg)

Loop diuretic, IV calcium, hemodialysis (if severe)

Question 25

What are the two types of hyponatremia?

Answer 25

Hypertonic hyponatremia (serum Osm over 280): Non-sodium osmoles are pulling fluid into the vascular space. “Pseudo” hyponatremia, meaning actual sodium levels are normal, they just get diluted

Hypotonic hyponatremia (serum Osm under 280): three types

Hypovolemic (Na and Water loss, ie Diarrhea/vomiting, loop diuretics)
Hypervolemic (Heart failure fluid retention, cirrhosis, renal failure)
Euvolemic (syndrome of inappropriate antidiuretic hormone, or SIADH; THIAZIDE diuretics)

Question 26

What sodium deficiency do loop diuretics cause? thiazide?

Answer 26

Loop: HYPOVOLEMIC

Thiazide: EUVOLEMIC

Question 27

What is SIADH?

Answer 27

Syndrome of Inappropriate Antidiuretic Hormone
Too much ADH/AVP, binds V2 in kidneys to insert aquaporins into the collecting duct.

Causes water to be reabsorbed (this water would normally be peed out)

Question 28

What are some drug causes of SIADH?

Answer 28

Carbamazepine/oxcarbazepine
Tricyclic antidepressants
SSRI's
Vasopressin/desmopressin
Cyclophosphamide
Vincristine

Question 29

Why shouldn’t hyponatremia be corrected as fast as possible?

Answer 29

Max 8mmol/24 hour because overcorrection has been associated with osmotic demyelination syndrome

Question 30

When is Conivaptan/Tolvaptan appropriate?

Answer 30

Treatment for hypervolemic or euvolemic hyponatremia (ie Heart failure, SIADH)

Conivaptan: max 4 days
Tolvaptan: max 30 days

Question 31

How to treat hypernatremia?

Answer 31

Correct the underlying cause (replace free water, d/c contributing drugs)

How to replace free water? Calculate free water deficit
Total body water x [(Serum Na/140)-1]

USE D5!

Max rate of correction: 10 mEq/24 hr

Question 32

What chloride imbalance causes Alkalosis? Acidosis?

Answer 32

HypOchloremia can cause Alkalosis

HypERchloremia can cause Acidosis

Question 33

How to calculate corrected calcium?

Answer 33

Serum Ca + 0.8 * (Normal albumin - Pt albumin)

Less than 8 mg/dL is hypocalcemia

Question 34

How do you treat hypercalcemia?

Answer 34

Ca less than 12 with mild or no symptoms: no aggressive measures, just adequately hydrate and avoid precipitants (thiazide diuretics, calcium intake)

Severe symptoms or Ca over 14:
NS infusion at 200-300 mL/hr
Calcitonin 4 units/kg every 12 hours
Zoledronic acid 4 mg IV or pamidronate 60-mg IV over 2 hrs
Steroids effective in some malignancies

Question 35

What are causes of hypophosphatemia?

Answer 35

Intracellular shift due to insulin/glucose
Drugs (phosphate binders, sucralfate)
Renal replacement therapy
Refeeding syndrome

Question 36

What is refeeding syndrome?

Answer 36

When a body that is malnourished is given glucose, a huge surge in insulin sends electrolytes into the cells, mostly phosphate causing hypophosphatemia.

Treatment is prevention! Slowly initiate feedings or hold and replace lytes first

Question 37

How do you treat hypophosphatemia?

Answer 37

Oral (preferred):
15-30 mmol NaPhos solution
2 packets Neutra-Phos (8mmol Phos, 7mEq K per packet)

IV: 15-30 mmol NaPhos or K-Phos (IV shortage currently going on)

Na vs K phos depends on levels of other lytes
Usually reserve IV for severe hypophosphatemia (less than 1 mg/dL)

Question 38

How do you treat hyperphosphatemia?

Answer 38

Dietary restriction of phosphorous
Phosphate binders (Ca-containing or sevelamer; avoid chronic Al containing)