Fluid Therapy

Question 1

Describe the main fluid compartments in the body and how much each makes up of the total body water

Answer 1

Body is made up of 65% water
-2/3 of that is intracellular
-1/3 of that is extracellular
-of the extracellular portion, 75% is interstitial and 25% is intravascular

Question 2

What is the equation for total body water?

Answer 2

BW X 0.65

Question 3

Describe the sodium and potassium content of intracellular vs extracellular fluid

Answer 3

Intracellular: low sodium, high potassium
Extracellular: high sodium, low potassium

Easy to remember if you think about chemistry values- sampling the extracellular compartment which has high sodium and low potassium values

Question 4

How can it be concluded that total body sodium determines hydration?

Answer 4

-water follows sodium
-sodium concentration determines IV volume

Question 5

Why is there naturally more sodium in the extracellular space than the intracellular space?

Answer 5

Due to the electrochemical gradient set up by the sodium-ATPase pumps
-sets up potential energy to perform cellular functions

Question 6

What is the definition of osmole? What about osmolality?

Answer 6

Osmole- number of moles in a solution that contributes to its hold on water
Osmolality- number of osmoles dissolved in a mass of solvent

Question 7

What are 2 ways you can get the osmolality of a substance in medicine?

Answer 7

Measure it or calculate it
-calculation is far more common

Question 8

What toxin can cause a large gap between measured and calculated osmolality?

Answer 8

Ethylene glycol
-there is always a little bit of a gap though in normal patients

Question 9

What can you infer from serum sodium concentrations?

Answer 9

Total body water
- does not tell you total body sodium content

*if serum sodium is decreased, can be due to excess water, if increased, can be due to decreased water
-serum sodium concentration when measured is dependent on the amount of water in the extravascular space

Question 10

What is the main cause of hyponatremia in clinical practice?

Answer 10

Anorexia
- losing salts and water to the environment but only taking in more water- dilutes sodium in the bloodstream

Question 11

What is the main cause of hypernatremia in clinical practice?

Answer 11

Dehydration
- loss of water leads to falsely elevated serum concentrations of sodium

Question 12

What is the most common type of fluid lost?

Answer 12

• isotonic (through vomiting, diarrhea, sweating, daily losses)
• if this is the case, sodium concentrations will be unchanged

Question 13

What can cause hypotonic losses or hypertonic losses and how will this affect the sodium?

Answer 13

Hypotonic: can occur with excessive polyuria (CKD patients)
- will cause hypernatremia

Hypertonic: losses are rare
- could lead to hyponatremia

Question 14

Describe the general types of fluid loss

Answer 14

Loss of fluid from interstitial space=dehydration
- usually occurs slowly over several days to weeks, can be replaced slowly

Loss of fluid from intravascular space=hypovolemia
-usually occurs more rapidly than with dehydration
-requires rapid restoration of blood volume

These are different, but they are both fluid lost from the extravascular space. Both require replacement fluid with high sodium

Question 15

What are the indications for giving fluids?

Answer 15

-Dehydration
-hypovolemia
-anorexia (if you are worried they will become dehydrated if you don’t put them on fluids)
-severe losses (severe diarrhea, polyuria)
-general anesthesia
-as a vehicle for medications

Question 16

What is the difference between crystalloids and colloids?

Answer 16

Crystalloids: salt water
- freely moves within the extracellular space and redistributes to the interstitial space rapidly

Colloids: contains molecules that dont readily leave the extravascular space, theoretically stays in IV space longer

Question 17

If you need to replace a lot of fluid fast, what is the preferred fluid to give?

Answer 17

Isotonic crystalloid
- replaces volume fast, but doesnt last long in the blood

Question 18

What results in the greatest increase in blood volume per volume delivered?

Answer 18

Hypertonic saline

Question 19

Which fluid will last the longest in the bloodstream before redistribution?

Answer 19

Colloids

Question 20

What are the cons associated with giving crystalloids or colloids?

Answer 20

Cystalloids: large volume needed, transient effect, can potentiate edema if too much is given

Colloids: potential interstitial leak leading to edema formation
-changes in coagulation
-kidney injury can result
-more expensive

Question 21

T/F: It is ok to use a synthetic colloid over a crystalloid

Answer 21

False- is not recommended
-no research shows this to have benefit, and there is a heightened risk of renal injury or coagulation problems

Question 22

What fluids used in medicine are isotonic?

Answer 22

Similar tonicity as normal blood (ECF)
-lactated ringers solution
-normal saline (0.9% NaCl)
-normosol R
-plasmalyte A

Question 23

What fluids used in medicine are hypotonic?

Answer 23

-0.45% sodium chloride
- normosol M and 5% dextrose

These cannot be bolused and have to be given slowly (will cause cells to swell and die)
- have to be given through a central catheter

Question 24

What fluids used in medicine are hypertonic?

Answer 24

-23.4% sodium chloride

Pulls free water from the interstitial and intracellular spaces to increase IV volume
-has a greater effect per mililiter of volume given
-allows for increased tissue oxygen delivery and decreased cellular edema (good in cases of cerebral edema)

AVOID IN DEHYDRATED OR HYPERNATREMIC PATIENTS

Question 25

What is the difference between balanced and unbalanced fluids?

Answer 25

Balanced: major electrolytes are in similar proportion to extracellular fluid (lower in chloride)
-includes Lactated ringers, normosol R, plasmalyte

Unbalances: electrolytes are not in proportion with ECF, though are often isotonic
-includes normal saline, 5% dextrose in water

*Chloride is lower than sodium in blood

Question 26

What are the main differences between replacement fluid and maintenance fluid?

Answer 26

Replacement fluid: mimics extracellular fluid (high in sodium)

Maintenance fluid: mimics daily requirements for electrolytes (low in sodium and chloride, high in potassium)

Question 27

T/F: LRS is a maintenance fluid

Answer 27

NO