Basic Principles of Medicine 1: Lecture 46
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Questions and Answers

What is one primary goal of measuring plasma volume using the indicator dilution principle?

  • To measure the distribution of electrolytes
  • To determine the extracellular fluid volume (correct)
  • To estimate total body water precisely
  • To assess fluid balance in dehydration

    • Which of the following is NOT included in the estimated compartments of body fluids?

  • Plasma volume
  • Interstitium
  • Adipose tissue (correct)
  • Intracellular space

    • How does an increase in extracellular fluid osmolality affect water movement between compartments?

  • Water diffuses across membranes equally
  • Water remains unchanged between compartments
  • Water influxes into the intracellular compartment
  • Water moves from the intracellular to extracellular compartment (correct)

    • Which of the following fluids has the lowest percentage of total body water in adults?

    <p>Plasma volume (B)</p> Signup and view all the answers

    What is the primary function of the indicator used to measure extracellular fluid volume?

    <p>It helps measure partition of total body water (B)</p> Signup and view all the answers

    What is the normal range for daily water intake in adults?

    <p>2 to 4 liters (C)</p> Signup and view all the answers

    Which volume is typically estimated to be the largest component of body water?

    <p>Intracellular fluid volume (D)</p> Signup and view all the answers

    What is the role of understanding water movement between fluid compartments in clinical practice?

    <p>To guide fluid replacement therapies (B)</p> Signup and view all the answers

    What is the function of antidiuretic hormone (ADH) in the regulation of water?

    <p>Controls the excretion of water by the kidneys (B)</p> Signup and view all the answers

    Which of the following represents the correct proportion of body water for males?

    <p>60% TBW (C)</p> Signup and view all the answers

    What percentage of total body water (TBW) does intracellular fluid (ICF) constitute?

    <p>55% (A)</p> Signup and view all the answers

    In a 70 kg man, what is the estimated volume of extracellular fluid (ECF)?

    <p>18.9 L (B)</p> Signup and view all the answers

    Which fluid compartment contributes the least to total body water?

    <p>Bone, cartilage, and connective tissue (B)</p> Signup and view all the answers

    What is the primary source of water loss from the body?

    <p>Kidneys (A)</p> Signup and view all the answers

    What is the fluid volume measurement method that involves indicators to estimate compartment volumes?

    <p>Indicator-dilution method (A)</p> Signup and view all the answers

    How does total body water (TBW) change with age?

    <p>It decreases (B)</p> Signup and view all the answers

    What indicator is used mainly for estimating Total Body Water (TBW)?

    <p>Tritiated water (D)</p> Signup and view all the answers

    How is the Intracellular Fluid (ICF) calculated?

    <p>TBW - ECF (A)</p> Signup and view all the answers

    What is the formula used to calculate compartment volume after equilibration?

    <p>V = Q/C (B)</p> Signup and view all the answers

    In the example involving 100 mL of D₂O, what is the calculated TBW?

    <p>36 L (A)</p> Signup and view all the answers

    Which indicator is primarily used to assess plasma volume?

    <p>Evans blue (B)</p> Signup and view all the answers

    What must occur for ICF volume changes to happen according to the Darrow-Yannet diagram?

    <p>Equilibration of osmolality (C)</p> Signup and view all the answers

    How must the amount of indicator be adjusted for accurate compartment volume calculation?

    <p>By accounting for excretion (B)</p> Signup and view all the answers

    What does the Darrow-Yannet diagram visualize?

    <p>Volume and osmolality changes in fluid compartments (D)</p> Signup and view all the answers

    What type of volume expansion is characterized by the addition of isotonic saline to the ECF?

    <p>Isosmotic volume expansion (C)</p> Signup and view all the answers

    Which of the following accurately describes hyperosmotic volume contraction?

    <p>It is caused by loss of hypotonic fluids. (C)</p> Signup and view all the answers

    In which scenario would hyposmotic volume expansion occur?

    <p>Ingestion of large amounts of water (A)</p> Signup and view all the answers

    What is the outcome of isosmotic volume contraction?

    <p>Stable osmolality but decreased ECF volume (A)</p> Signup and view all the answers

    What effect does a hyperosmotic volume expansion have on the distribution of water between the ICF and ECF?

    <p>Water moves from the ICF to the ECF. (B)</p> Signup and view all the answers

    What effect does a deficiency in aldosterone have on extracellular fluid volume?

    <p>Decreases ECF volume and sodium concentration (C)</p> Signup and view all the answers

    Which formula represents plasma osmolality?

    <p>2 x Na (mEq/L) + glucose (mg/dL) /18 + BUN (mg/dL)/2.8 (D)</p> Signup and view all the answers

    What characterizes hyposmotic volume contraction?

    <p>Decreased sodium concentration leads to volume changes between ECF and ICF. (A)</p> Signup and view all the answers

    Flashcards

    Body Water Compartments

    The different fluid-filled spaces within the body, including intracellular and extracellular fluids.

    Total Body Water (TBW)

    The total amount of water in the entire body.

    Extracellular Fluid (ECF)

    Body fluid outside the cells.

    Intracellular Fluid (ICF)

    Body fluid inside the cells.

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    Plasma Volume

    The amount of fluid within the blood plasma.

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    Blood Volume

    The total amount of blood in the body.

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    Indicator Dilution Principle

    A method to measure fluid volumes using a tracer substance.

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    Water Intake/Loss

    The routes and amounts of water entering and leaving the body.

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    Interstitial Fluid (ISF)

    Fluid surrounding cells, a component of the extracellular fluid.

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    % of TBW in Men

    60% of a man's total weight.

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    % of TBW in Women

    55% of a woman's total weight.

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    Water Gain Mechanisms (in L)

    Liquid consumption (1-2L), water in food (0.8-1L), and metabolic water (0.3-0.4L).

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    Water Loss Mechanisms (in L)

    Kidney excretion (1-2L), skin evaporation (0.6L), lung respiration (0.3L), and feces (0.2L).

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    Plasma Volume Calculation

    Calculate plasma volume by dividing amount injected (and not excretd) by plasma indicator concentration.

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    Compartment Volume Formula

    Compartment volume equals the difference between the injected amount and the excreted amount divided by the plasma concentration.

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    ICF Calculation

    Intracellular fluid is calculated by subtracting ECF from TBW.

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    ISF Calculation

    Interstitial fluid volume is calculated by subtracting the plasma volume from the ECF volume.

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    Darrow-Yannet Diagram

    A diagram showing how changes in ECF volume and osmolality affect the ICF and ECF.

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    Osmolality Equilibration

    ICF and ECF osmolality stay equal because of osmotic equilibrium.

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    Isosmotic volume expansion

    Expanding extracellular fluid (ECF) volume by adding a solution with the same osmolality as body fluids, like isotonic saline.

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    Hyperosmotic volume expansion

    Increasing ECF volume by adding a solution with higher osmolality than body fluids, like hypertonic saline. Water moves from intracellular fluid (ICF) to ECF.

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    Hyposmotic volume expansion

    Increasing ECF volume by adding a solution with lower osmolality than body fluids, like hypotonic solutions. Water moves into cells.

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    Isosmotic volume contraction

    Reducing ECF volume by losing an isotonic fluid (same osmolality as body fluids).

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    Hyperosmotic volume contraction

    Reducing ECF volume by losing a hypotonic fluid (lower osmolality than body fluids). Water moves from ICF to ECF.

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    Hyposmotic volume contraction

    Reducing ECF volume with a decrease in sodium concentration. Water moves from ECF to ICF.

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    Plasma Osmolality Formula

    2 x Na (mEq/L) + glucose (mg/dL) /18 + BUN (mg/dL)/2.8

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    Isotonic Saline

    0.9% NaCl solution, has the same osmolality as body fluids

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    Study Notes

    Basic Principles of Medicine 1, Module: Cardiovascular, Pulmonary, Renal, Lecture No: 46, Distribution of Body Fluids

    • Learning Objectives:
      • List major routes and normal ranges for water intake and loss.
      • Given body weight, estimate total body water, extracellular fluid volume, intracellular fluid volume, interstitial fluid volume, plasma volume, and blood volume.
      • Demonstrate the ability to use the indicator dilution principle to measure plasma volume, blood volume, extracellular fluid volume, total body water, and identify compounds used to measure each volume.
      • Explain the water movement between intracellular and extracellular fluid compartments caused by increases or decreases in extracellular fluid osmolality.

    Water Gain and Water Loss

    • Water Gain:

      • Liquid consumption (1-2 L)
      • Water in food (0.8-1 L)
      • Metabolic water (0.3-0.4 L)

    • Water Loss:

      • Kidneys (1-2 L)
      • Skin (0.6 L)
      • Lungs (0.3 L)
      • Fecal loss (0.2 L)

    Body Fluid Distribution

    • Total Body Water (TBW):
      • Females: 55% of body weight
      • Males: 60% of body weight
      • Decreases with age and in obese individuals
    • Intracellular Fluid (ICF): 55% of TBW
    • Extracellular Fluid (ECF): 45% of TBW
    • Interstitial Fluid (ISF): ~20% of ECF
    • Plasma volume (PV): ~8% of ECF
    • Blood volume (BV): calculable using PV and hematocrit

    Fluid Spaces of the ECF

    • Interstitial Fluid (ISF): 20%
    • Plasma: 8%
    • Bone, cartilage, connective tissue, fluid: 17%
    • ICF and ISF are rapidly interchangeable (interchangeable)
      • ECF = (plasma +ISF)
      • Plasma is 1/3 of ECF (1/3 of ECF = 8% which is less than ~20% of ISF)
      • Therefore, ICF = 2/3 TBW and ~rapid ECF = 1/3 TBW

    Example Calculations (Example 1 & 2)

    • Using body weight and hematocrit, calculations determine TBW, ICF, ECF, ISF, plasma volume, and blood volume
    • Using a given formula, example calculations illustrate how to determine TBW from administered isotopes and plasma concentration

    Fluid Compartment Volume Measurement

    • Techniques: Indicator-dilution method used to estimate volumes of various compartments
    • Compartments: TBW, ECF, Plasma
    • Indicator Examples: Isotopic water (heavy water, D₂O), tritiated water (HTO), radioactive sodium, sulfate, mannitol, inulin, radioactive albumin, Evans blue.
    • Indirect Calculation: ICF and Interstitial Fluid (ISF) estimated. ICF = TBW - ECF. ISF = ECF
    • Formula: V = Q/C ; where V = compartment volume, Q = amount injected - amount excreted, C = concentration of the indicator in plasma after equilibration

    Compartment Volume Formula

    • Formula for calculating compartment volume using injected indicator amounts and plasma concentration after equilibration.

    Summary- Volume and Osmolality Changes

    • Diagrams illustrating different types of volume expansion and contraction, along with corresponding changes in osmolality.

    Intravenous Fluids

    • Isotonic: 0.9% NaCl, Ringers solution
    • Hypotonic: 0.45% NaCl, 5% dextrose
    • Hypertonic: 5% dextrose in 0.9% NaCl, 3% NaCl

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    St. George's University Lecture Notes: Basic Principles of Medicine 1 - PDF

    Description

    Explore the distribution of body fluids through an overview of water gain and loss. This quiz will help you understand the major routes of water intake, estimates of body water volumes, and the implications of fluid movement between compartments. Test your knowledge on the key principles involved in the cardiovascular, pulmonary, and renal systems.

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