Fluids

Question 1

Describe how total body water is distributed

Answer 1

TBW = 50-60% of body weight
- 2/3 of that is intracellular fluid
- 1/3 of that is extracellular fluid. Within that:
– 3/4 is interstitial fluid (between cells)
– 1/4 is plasma (within blood vessels)

Question 2

Water moves freely from one compartment to another. This is called?

Answer 2

Diffusion

Question 3

True or False? Movement of electrolytes (e.g., Na+, K+, Cl-, PO4-) from ICF <-> ECF does not require active transport

Answer 3

False - requires active transport

Question 4

Extracellular fluid (ECF) osmolality is maintained primarily by ______

Answer 4

sodium (and its anion counterparts chloride and bicarb)

Question 5

Intracellular fluid (ICF) osmolality is determined by _________ concentration

Answer 5

potassium (and its accompanying anion proteins and phosphate)

Question 6

Water moves freely across cell and vascular membranes. How so?

Answer 6

Following sodium to keep intra/extracellular osmolality equal

Question 7

Proteins are present within cellular ___ and within _____ _______, but not within the ____________ ___

Answer 7

ICF; blood vessels; interstitial ECF

Question 8

What is the tonicity of D5W?

Answer 8

Hypotonic

Question 9

What is the tonicity of 0.45% NaCl?

Answer 9

Hypotonic

Question 10

What is the tonicity of Lactated Ringer’s?

Answer 10

Isotonic

Question 11

What is the tonicity of 0.9% NaCl?

Answer 11

Isotonic

Question 12

What is the tonicity of 3% NaCl?

Answer 12

Hypertonic

Question 13

Should come back to slide 10 to get an idea of what is in each of these IV solutions

Answer 13

pls

Question 14

How do cells regulate their internal volume?

Answer 14

In response to osmostic stress by activation of membrane carrier proteins and channels

Question 15

Despite protective mechanisms, rapid and/or extreme changes in osmolality can cause cell swelling or shrinkage. What can plasma hyper-osmolality lead to?

Answer 15

1. Brain cell shrinkage –>
2. Somnolence, confusion –>
3. If severe enough can lead to cerebral bleeding, death

Question 16

Despite protective mechanisms, rapid and/or extreme changes in osmolality can cause cell swelling or shrinkage. What can plasma hypo-osmolality lead to?

Answer 16

1. Brain cell swelling –>
2. Headache, N+V, gait instability –>
3. Seizures, coma, death

Question 17

Define plasma osmolality

Answer 17

Concentration of effective solutes in plasma (relative to water)

Question 18

What do osmoreceptors do? (3)

Answer 18

1. The body’s ability to sense and respond to changes in plasma osmolality is mediated by osmoreceptors
2. Specialized cells that recognize changes in plasma osmolality and initiate corrective actions by the release of hormones, etc.
3. These are key to regulating water homeostasis

Question 19

What are 2 scenarios in which Vasopressin/Antidiuretic Hormone (ADH) is released in the body?

Answer 19

1. Released in response to increased plasma osmolality (as sensed by osmoreceptors)
2. Also released in response to non-osmotic stimuli when osmoreceptors in the brain detect decreased circulating blood volume or decreased blood pressure

Question 20

ADH released in response to increased plasma osmolality. What is ADH doing in this case? (3)

Answer 20

1. Stimulates water reabsorption in the distal tubule/collecting duct of the kidney (↓ diuresis) -> excretion of a
   more concentrated urine
2. Also stimulates thirst
3. These corrective measures increase the amount of water in the circulation, restoring plasma osmolality to normal

Question 21

ADH released in response to non-osmotic stimuli when osmoreceptors in the brain detect decreased circulating blood volume or decreased blood pressure. Why is ADH released in this situation and what is it doing? (5)

Answer 21

1. Sensed volume depletion e.g. diarrhea, vomiting
2. Poor kidney perfusion e.g. decompensated heart failure, severe cirrhosis
3. Requiring the maintenance of blood pressure e.g. cardiovascular collapse, extreme blood loss
4. Pain, hypoxia, acidosis
5. In this case, water conservation restores circulating blood volume at the expense of decreased serum osmolality –> dilutional hyponatremia

Question 22

Aldosterone is a ________________ released by the _______ ______

Answer 22

mineralocorticoid; adrenal cortex

Question 23

Describe what aldosterone does (3)

Answer 23

1. Decreased blood volume or decreased blood pressure activates Renin-Angiotensin-Aldosterone System (RAAS) –> stimulates release of aldosterone
2. Increased serum K+ or decreased serum Na+ can also stimulate aldosterone release
3. Stimulates reabsorption of sodium from the distal convoluted tubule of the kidney -> increases serum Na+ (and therefore water because water follows sodium) and decreases serum K+

Question 24

What does natriuretic peptides (ANP and BNP) do/when are they released? (3)

Answer 24

1. Released by the atria/ventricles of the heart in response to ↑ blood pressure and/or ↑ blood volume
2. Inhibit the activity of aldosterone by ↓ sympathetic nervous system activity (↓ RAAS activation)
   - Also ↑ vasodilation
3. Have opposite effects of ADH and aldosterone!

Question 25

Describe the role of the kidney in terms of fluid balance

Answer 25

Kidney regulates water excretion to keep serum osmolality relatively constant (275-290 mOsm/kg) despite variability in water intake

Question 26

Serum osmolality is determined by what 3 things?

Answer 26

1. Sodium concentration - primary 2. Glucose (small) 3. Urea (small)

Question 27

The goal of fluid/electrolyte administration is what?

Answer 27

Maintain homeostasis - Best way to do this is to continue eating and drinking normally if possible

Question 28

If it is not possible to eat/drink normally, fluid losses will need to be replenished. How are we losing these fluids? What is the minimum amount of fluids needed per day?

Answer 28

1. Fluid loss in urine + fluid loss in stool + insensible fluid loss from skin, respiratory tract 2. Minimum amount of fluids needed per day ~1400mL (or 60mL/hr)

Question 29

Maintenance fluid therapy includes: (3)

Answer 29

1. Water 2. Electrolytes (usually 75-175 mEq sodium and 20-60 mEq potassium per day) 3. Dextrose 100-150 g/d to prevent protein catabolism and starvation ketoacidosis

Question 30

Hypovolemic patient --> volume depletion generally results from what?

Answer 30

Decreased total body sodium due to renal or extrarenal sodium loss from the ECF - Renal losses can be due to ↑ diuresis, salt-wasting nephropathies, mineralcorticoid deficiencies - Extra-renal losses can be due to fluid loss from the GI tract (e.g. vomiting, diarrhea), skin losses (e.g. burns), hemorrhage, or increased capillary permeability (“third-spacing” in critical illness due to anaphylaxis, sepsis, etc)

Question 31

We have to lose A LOT of free water to cause volume depletion. Why?

Answer 31

Because most of our water is in the ICF (volume contraction assesses ECF and specifically intravascular which only accounts for ~8.5% of TBW)

Question 32

Mild volume depletion may be ____________ Severe volume depletion may lead to ______ ______ _________, _____ ________, and ___________ _____

Answer 32

asymptomatic; mental status changes, renal failure, hypovolemic shock

Question 33

Symptoms of hypovolemia include: (4)

Answer 33

1. Thirst 2. Fatigue 3. Muscle cramps 4. Orthostatic dizziness

Question 34

What are the signs hypovolemia? (3)

Answer 34

1. Decreased jugular venous pressure (JVP) 2. Postural hypotension and postural tachycardia 3. Decreased sweat

Question 35

Mild hypovolemia can be corrected ______

Answer 35

orally

Question 36

When might IV therapy be needed to treat hypovolemia? (3)

Answer 36

1. Symptomatic fluid loss 2. Hemodynamic instability 3. Intolerance to oral administration (Frequent reassessment of fluid status is required to prevent over-correction)

Question 37

What is the goal of hypovolemia treatment?

Answer 37

Replenish intravascular volume by expanding the ECF compartment (use sodium-based solutions because the sodium will remain in the ECF)

Question 38

How is hypovolemia (IV) treated?

Answer 38

Use isotonic fluids – contain sodium concentration similar to that of the plasma fluid in the ECF -> therefore will remain in the ECF space - Normal saline (0.9%) generally preferred - In massive hemorrhage or GI bleeding, blood transfusion can accomplish both intravascular volume expansion and correction of anemia

Question 39

How can/should fluids be administered when treating hypovolemia (IV)?

Answer 39

Fluids can be administered as a bolus or at a steady infusion rate - With symptomatic volume depletion, usually administer a 1-2 L bolus to expand intravascular space more quickly - Caution with poor cardiac function or peripheral edema - Watch for volume overload

Question 40

Why can we not just administer water IV to correct hypovolemia?

Answer 40

- Well, most water is found inside the cells. - If we need more plasma volume, giving free water is going to go straight into cells and wont stay in the blood vessels, which is where we need to restore the blood volume back to normal. - That's why we use isotonic solution in order to hold water in the blood vessels where it's needed in order to replenish the fluid volume.

Question 41

What may hypervolemia be a result of? (2)

Answer 41

1. Hypervolemia may result from a surplus of total body sodium (disorder of renal sodium retention) 2. Also may result from decreased effective circulating volume (e.g. heart failure, cirrhosis, or profound hypoalbuminemia)

Question 42

Expansion of the interstitial fluid compartment of the ECF (hypervolemia) may result in... (3)

Answer 42

1. Peripheral edema 2. Ascites 3. Pleural effusions

Question 43

Expansion of the intravascular compartment of the ECF (hypervolemia) may result in... (4)

Answer 43

1. Increased JVP 2. Pulmonary rales 3. An S3 heart sound 4. Elevated blood pressure

Question 44

Symptoms of hypervolemia include? (4)

Answer 44

1. Dyspnea 2. Orthopnea 3. Leg swelling 4. Abdominal distention

Question 45

Signs and symptoms of hypervolemia do not usually appear until...

Answer 45

~3-4 L of fluid retention has occurred - Rapid weight gain may be the earliest way to detect that someone is retaining fluid

Question 46

For hypervolemia it is important to address the __________ _____

Answer 46

underlying cause (i.e., HF, liver disease, or kidney disease)

Question 47

Hypervolemia: sodium excess can be managed with? (2)

Answer 47

1. Dietary sodium restriction 2. Diuretics - Thiazides - Loop diuretics - Potassium-sparing diuretics

Question 48

What is the MOA of thiazides?

Answer 48

Block NaCl transporters in the distal convoluted tubule. May work for mild sodium retention; however, thiazide diuretic use often results in compensatory increased sodium and water reabsorption in the proximal tubule

Question 49

What is the MOA of loop diuretics?

Answer 49

Block Na+/K+/2Cl- transporter in the thick ascending loop of Henle. They increase water excretion, and also loss of calcium and magnesium. Preferred for brisk and immediate diuresis

Question 50

What is the MOA of potassium-sparing diuretics?

Answer 50

Decrease Na+ reabsorption in the collecting duct. Relatively small diuretic effect but may be useful adjunctive agents

Question 51

What effect do thiazide diuretics have on the following: 1. Sodium 2. Potassium 3. Magnesium 4. Calcium

Answer 51

1. Decrease 2. Decrease 3. Decrease 4. Increase

Question 52

What effect do loop diuretics have on the following: 1. Sodium 2. Potassium 3. Magnesium 4. Calcium

Answer 52

1. Neutral 2. Decrease 3. Decrease 4. Decrease

Question 53

What effect do potassium-sparing diuretics have on the following: 1. Sodium 2. Potassium 3. Magnesium 4. Calcium

Answer 53

1. Neutral 2. Increase 3. Neutral 4. Neutral