Fluids Flashcards
Describe how total body water is distributed
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)
Water moves freely from one compartment to another. This is called?
Diffusion
True or False? Movement of electrolytes (e.g., Na+, K+, Cl-, PO4-) from ICF <-> ECF does not require active transport
False - requires active transport
Extracellular fluid (ECF) osmolality is maintained primarily by ______
sodium (and its anion counterparts chloride and bicarb)
Intracellular fluid (ICF) osmolality is determined by _________ concentration
potassium (and its accompanying anion proteins and phosphate)
Water moves freely across cell and vascular membranes. How so?
Following sodium to keep intra/extracellular osmolality equal
Proteins are present within cellular ___ and within _____ _______, but not within the ____________ ___
ICF; blood vessels; interstitial ECF
What is the tonicity of D5W?
Hypotonic
What is the tonicity of 0.45% NaCl?
Hypotonic
What is the tonicity of Lactated Ringer’s?
Isotonic
What is the tonicity of 0.9% NaCl?
Isotonic
What is the tonicity of 3% NaCl?
Hypertonic
Should come back to slide 10 to get an idea of what is in each of these IV solutions
pls
How do cells regulate their internal volume?
In response to osmostic stress by activation of membrane carrier proteins and channels
Despite protective mechanisms, rapid and/or extreme changes in osmolality can cause cell swelling or shrinkage. What can plasma hyper-osmolality lead to?
- Brain cell shrinkage –>
- Somnolence, confusion –>
- If severe enough can lead to cerebral bleeding, death
Despite protective mechanisms, rapid and/or extreme changes in osmolality can cause cell swelling or shrinkage. What can plasma hypo-osmolality lead to?
- Brain cell swelling –>
- Headache, N+V, gait instability –>
- Seizures, coma, death
Define plasma osmolality
Concentration of effective solutes in plasma (relative to water)
What do osmoreceptors do? (3)
- The body’s ability to sense and respond to changes in plasma osmolality is mediated by osmoreceptors
- Specialized cells that recognize changes in plasma osmolality and initiate corrective actions by the release of hormones, etc.
- These are key to regulating water homeostasis
What are 2 scenarios in which Vasopressin/Antidiuretic Hormone (ADH) is released in the body?
- Released in response to increased plasma osmolality (as sensed by osmoreceptors)
- Also released in response to non-osmotic stimuli when osmoreceptors in the brain detect decreased circulating blood volume or decreased blood pressure
ADH released in response to increased plasma osmolality. What is ADH doing in this case? (3)
- Stimulates water reabsorption in the distal tubule/collecting duct of the kidney (↓ diuresis) -> excretion of a
more concentrated urine - Also stimulates thirst
- These corrective measures increase the amount of water in the circulation, restoring plasma osmolality to normal
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)
- Sensed volume depletion e.g. diarrhea, vomiting
- Poor kidney perfusion e.g. decompensated heart failure, severe cirrhosis
- Requiring the maintenance of blood pressure e.g. cardiovascular collapse, extreme blood loss
- Pain, hypoxia, acidosis
- In this case, water conservation restores circulating blood volume at the expense of decreased serum osmolality –> dilutional hyponatremia
Aldosterone is a ________________ released by the _______ ______
mineralocorticoid; adrenal cortex
Describe what aldosterone does (3)
- Decreased blood volume or decreased blood pressure activates Renin-Angiotensin-Aldosterone System (RAAS) –> stimulates release of aldosterone
- Increased serum K+ or decreased serum Na+ can also stimulate aldosterone release
- 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+
What does natriuretic peptides (ANP and BNP) do/when are they released? (3)
- Released by the atria/ventricles of the heart in response to ↑ blood pressure and/or ↑ blood volume
- Inhibit the activity of aldosterone by ↓ sympathetic nervous system activity (↓ RAAS activation)
- Also ↑ vasodilation - Have opposite effects of ADH and aldosterone!
Describe the role of the kidney in terms of fluid balance
Kidney regulates water excretion to keep serum osmolality relatively constant (275-290 mOsm/kg) despite variability in water intake
Serum osmolality is determined by what 3 things?
- Sodium concentration - primary
- Glucose (small)
- Urea (small)
The goal of fluid/electrolyte administration is what?
Maintain homeostasis
- Best way to do this is to continue eating and drinking normally if possible
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?
- Fluid loss in urine + fluid loss in stool + insensible fluid loss from skin, respiratory tract
- Minimum amount of fluids needed per day ~1400mL (or 60mL/hr)
Maintenance fluid therapy includes: (3)
- Water
- Electrolytes (usually 75-175 mEq sodium and 20-60 mEq potassium per day)
- Dextrose 100-150 g/d to prevent protein catabolism and starvation ketoacidosis
Hypovolemic patient –> volume depletion generally results from what?
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)
We have to lose A LOT of free water to cause volume depletion. Why?
Because most of our water is in the ICF (volume contraction assesses ECF and specifically intravascular which only accounts for ~8.5% of TBW)
Mild volume depletion may be ____________
Severe volume depletion may lead to ______ ______ _________, _____ ________, and ___________ _____
asymptomatic;
mental status changes, renal failure, hypovolemic shock
Symptoms of hypovolemia include: (4)
- Thirst
- Fatigue
- Muscle cramps
- Orthostatic dizziness
What are the signs hypovolemia? (3)
- Decreased jugular venous pressure (JVP)
- Postural hypotension and postural tachycardia
- Decreased sweat
Mild hypovolemia can be corrected ______
orally
When might IV therapy be needed to treat hypovolemia? (3)
- Symptomatic fluid loss
- Hemodynamic instability
- Intolerance to oral administration
(Frequent reassessment of fluid status is required to prevent over-correction)
What is the goal of hypovolemia treatment?
Replenish intravascular volume by expanding the ECF compartment (use sodium-based solutions because the sodium will remain in the ECF)
How is hypovolemia (IV) treated?
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
How can/should fluids be administered when treating hypovolemia (IV)?
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
Why can we not just administer water IV to correct hypovolemia?
- 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.
What may hypervolemia be a result of? (2)
- Hypervolemia may result from a surplus of total body sodium (disorder of renal sodium retention)
- Also may result from decreased effective circulating volume (e.g. heart failure, cirrhosis, or profound hypoalbuminemia)
Expansion of the interstitial fluid compartment of the ECF (hypervolemia) may result in… (3)
- Peripheral edema
- Ascites
- Pleural effusions
Expansion of the intravascular compartment of the ECF (hypervolemia) may result in… (4)
- Increased JVP
- Pulmonary rales
- An S3 heart sound
- Elevated blood pressure
Symptoms of hypervolemia include? (4)
- Dyspnea
- Orthopnea
- Leg swelling
- Abdominal distention
Signs and symptoms of hypervolemia do not usually appear until…
~3-4 L of fluid retention has occurred
- Rapid weight gain may be the earliest way to detect that someone is retaining fluid
For hypervolemia it is important to address the __________ _____
underlying cause (i.e., HF, liver disease, or kidney disease)
Hypervolemia: sodium excess can be managed with? (2)
- Dietary sodium restriction
- Diuretics
- Thiazides
- Loop diuretics
- Potassium-sparing diuretics
What is the MOA of thiazides?
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
What is the MOA of loop diuretics?
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
What is the MOA of potassium-sparing diuretics?
Decrease Na+ reabsorption in the collecting duct. Relatively small diuretic effect but may be useful adjunctive agents
What effect do thiazide diuretics have on the following:
1. Sodium
2. Potassium
3. Magnesium
4. Calcium
- Decrease
- Decrease
- Decrease
- Increase
What effect do loop diuretics have on the following:
1. Sodium
2. Potassium
3. Magnesium
4. Calcium
- Neutral
- Decrease
- Decrease
- Decrease
What effect do potassium-sparing diuretics have on the following:
1. Sodium
2. Potassium
3. Magnesium
4. Calcium
- Neutral
- Increase
- Neutral
- Neutral
