Water and Electrolyte Disorders

Question 1

What are the body fluid compartments?

Answer 1

ICF and ECF

Question 2

ECF is subdivided into what components?

Answer 2

Interstitial, vascular

Question 3

What is the major ECF cation?

Answer 3

Na

Question 4

What is the major ICF cation?

Answer 4

K

Question 5

What is the major ECF anion?

Answer 5

Cl

Question 6

What is the major ICF cation?

Answer 6

Phosphate

Question 7

Define plasma osmolality.

Answer 7

The number of solutes in plasma

Question 8

POsm = ?

Answer 8

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

Question 9

What is a normal POsm?

Answer 9

275-295 mOsm/kg

Question 10

What is the major determinant of plasma osmolality?

Answer 10

Na

Question 11

How does effective osmolality (EOsm) differ from plasma osmolality?

Answer 11

POsm - BUN/2.8 (urea diffuses between ICF and ECF and thus does not affect the osmotic gradient)

Question 12

Detail the movement of water between ECF and ICF compartments of differing osmolalities.

Answer 12

Water from from low solute concentration to high solute concentration

Question 13

What effect does hyponatremia have on the movement of water?

Answer 13

Water moves from ECF to ICF

Question 14

What effect does hypernatremia/hyperglycemia have on the movement of water?

Answer 14

Water moves from ICF to ECF

Question 15

Decreased TBNa presents with what clinical exam findings?

Answer 15

Signs of volume depletion- Decreased skin turgor, dry mucous membranes, decreased BP, increased pulse

Question 16

The movement of fluid across a capillary into the interstitial space is driven by Starling forces. What changes result in the movement of fluid out of capillaries into the interstitial space?

Answer 16

Decrease in plasma oncotic pressure and/or increased hydrostatic pressure

Question 17

Define isotonic fluid loss.

Answer 17

Net isotonic loss of Na + H2O

Question 18

Give an example of isotonic fluid loss.

Answer 18

Secretory diarrhea (adults)

Question 19

What clinical signs indicate isotonic fluid loss.

Answer 19

Signs of volume depletion

Question 20

What are the expected values for POsm and serum sodium with isotonic fluid loss?

Answer 20

Normal- hypovolemic normonatremia

Question 21

Detail the osmotic gradient between the ICF and ECF with isotonic loss of fluid.

Answer 21

No gradient or fluid shifts between compartments. ECF volume is contracted, but ICF volume remains the same.

Question 22

Define isotonic gain of fluid.

Answer 22

Net isotonic gain of Na + H2O

Question 23

What are the expected values for POsm and serum sodium with isotonic fluid gain?

Answer 23

Normal- hypervolemic normonatremia

Question 24

Detail the osmotic gradient between the ICF and ECF with isotonic gain of fluid.

Answer 24

No gradient or fluid shifts between compartments. ECF volume is expanded, but ICF volume remains the same.

Question 25

What is the composition of normal saline?

Answer 25

9g NaCl/L = 0.9%

Question 26

How can you treat isotonic gain of fluid?

Answer 26

Restrict sodium and water. Loop diuretics

Question 27

What physical exam finding may be present in a patient with an isotonic gain of fluid?

Answer 27

Pitting edema

Question 28

What is always present with hypotonic fluid disorders?

Answer 28

Hyponatremia

Question 29

Detail the osmotic gradient between the ECF and the ICF with hypotonic fluid disorders.

Answer 29

Fluid moves from ECF into ICF

Question 30

What processes can lead to a hypotonic fluid disorder.

Answer 30

Loss of hypertonic solution, gain of pure water, or gain of hypotonic solution

Question 31

Define hypertonic loss of fluid.

Answer 31

Loss of Na in excess of water

Question 32

What are the expected values for POsm and serum sodium with hypertonic fluid loss?

Answer 32

Decreased- hypovolemic hyponatremia

Question 33

Detail the osmotic gradient between the ICF and ECF with hypertonic loss of fluid.

Answer 33

Fluid flows from ECF into ICF. ECF is volume is contracted. ICF volume is expanded.

Question 34

List examples of conditions that can lead to hypertonic fluid loss.

Answer 34

Loop diuretics/thiazides (excessive), Addison disease, 21-hydroxylase deficiency

Question 35

What is the treatment for hypertonic fluid loss?

Answer 35

Normal saline

Question 36

Why are sodium containing fluids given slowly, especially in alcoholics?

Answer 36

Avoid central pontine myelinolysis

Question 37

What are the expected values for POsm and serum sodium with a gain in pure water?

Answer 37

Decreased- euvolemic hyponatremia

Question 38

Detail the osmotic gradient between the ICF and the ECF with gain in pure water.

Answer 38

Fluid moves from ECF into ICF. ECF and ICF are volume expanded.

Question 39

When checking skin turgor in a patient with gain in pure water, what finding would you expect?

Answer 39

Normal, because TBNa is normal

Question 40

What conditions lead to a gain in pure water?

Answer 40

SIADH, compulsive water drinking

Question 41

What is the treatment for gain in pure water?

Answer 41

Restrict water

Question 42

A serum sodium less than 120 indicates what disease process?

Answer 42

SIADH

Question 43

What are the expected values for POsm and serum sodium with a gain of hypotonic solution?

Answer 43

Decreased- hypervolemic hyponatremia

Question 44

Detail the change in volume of the ICF and the ECF with gain of hypotonic solution.

Answer 44

Expansion of both compartments.

Question 45

How is pitting edema related to gain of hypotonic solution.

Answer 45

With RHF (increased venous hydrostatic pressure) or cirrhosis/nephrotic syndrome (decreased oncotic pressure), CO is decreased. This is because fluid is trapped in the interstitial space. Decreased CO results in activation of the renin-angiotensin-aldosterone system. This causes the kidney to reabsorb a slightly hypotonic solution. When this occurs the fluid ends up in the interstitial space, which exacerbates pitting edema.

Question 46

What conditions lead to hypervolemic hyponatremia?

Answer 46

RHF, cirrhosis, nephrotic syndrome

Question 47

How do you treat gain in hypotonic solution (hypervolemic hyponatremia)?

Answer 47

Restrict water and salt. Diuretics