Henry's Law in Anesthesia
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Questions and Answers

According to Henry's Law, what is the relationship between the amount of gas that dissolves in a liquid and the partial pressure of the gas at a constant temperature?

  • Inversely proportional
  • Exponentially proportional
  • Not related
  • Directly proportional (correct)

    • What is the purpose of 'overpressurizing' in the context of volatile anesthetics?

  • To increase the concentration of anesthetic delivered, increasing the amount dissolved in the blood and speeding uptake (correct)
  • To decrease the alveolar concentration of the anesthetic
  • To slow down the uptake of the anesthetic into the blood
  • To reduce the partial pressure of the anesthetic in the gas phase

    • If a patient has a PaO2 of 400 mmHg, approximately how much O2 is dissolved in their arterial blood (in ml O2 / 100 ml blood)?

  • 0.6
  • 0.3
  • 1.2 (correct)
  • 1.5

    • If the inspired oxygen concentration (FiO2) is 50%, what is the estimated PaO2 and the approximate amount of O2 dissolved in 100 ml of blood?

    <p>PaO2 = 250 mmHg, dissolved O2 = 0.75 ml (D)</p> Signup and view all the answers

    How much CO2 is dissolved in arterial blood when the PaCO2 is 60 mmHg?

    <p>4.02 ml CO2/100 ml blood (D)</p> Signup and view all the answers

    According to Raoult's Law, what happens to the vapor pressure of a solvent when a solute is added?

    <p>It decreases because solute molecules occupy escape sites at the surface. (A)</p> Signup and view all the answers

    Which of the following best describes the mathematical relationship in Raoult's Law?

    <p>$P = \chi P_o$ (B)</p> Signup and view all the answers

    What is the primary difference between Henry's Law and Raoult's Law?

    <p>Henry's Law describes what happens when you have a gas over a solution, while Raoult's Law describes vapor pressure of a solution based on mole fraction. (D)</p> Signup and view all the answers

    According to Raoult's Law, what colligative property is observed over a solution when a non-volatile solute is mixed with a solvent?

    <p>Vapor pressure lowering (B)</p> Signup and view all the answers

    What is the effect of increased solute concentration on the boiling point of a solution?

    <p>The boiling point increases proportionally to the solute concentration. (B)</p> Signup and view all the answers

    How does the presence of solute particles affect the freezing point of a solution?

    <p>Solute particles interfere with the formation of a crystalline lattice, lowering the freezing point. (B)</p> Signup and view all the answers

    Which factor does NOT directly affect the rate of diffusion of a fluid through a permeable membrane?

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

    What is the relationship between molecular weight and diffusion rate, according to Graham's Law?

    <p>Diffusion rate is inversely proportional to the square root of the molecular weight. (C)</p> Signup and view all the answers

    If two solutions are separated by a semipermeable membrane, and one solution has a higher solute concentration, what process will occur?

    <p>Water will move from the lower concentration to the higher concentration. (B)</p> Signup and view all the answers

    What is the primary determinant of intravascular volume?

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

    How does temperature affect kinetic energy and the movement of molecules in a fluid?

    <p>Temperature is directly proportional to kinetic energy, increasing molecular movement. (C)</p> Signup and view all the answers

    What is oncotic pressure and what primarily creates it in capillaries?

    <p>The osmotic pressure exerted by plasma proteins, primarily created by albumin. (C)</p> Signup and view all the answers

    If a red blood cell is placed in a hypertonic solution, what will happen to the cell?

    <p>Water will move out of the cell, causing it to shrink. (B)</p> Signup and view all the answers

    Flashcards

    Henry's Law

    At constant temperature, gas solubility in a liquid is proportional to its partial pressure.

    Overpressurizing

    Increasing the partial pressure of volatile anesthetic to enhance blood uptake.

    Dissolved O2 in blood

    Amount of O2 dissolved is 0.003 ml/100 ml blood/mmHg partial pressure.

    Calculating dissolved O2

    Multiply partial pressure of O2 by 0.003 to find O2 in blood.

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    Dissolved CO2 in blood

    Amount of CO2 dissolved is 0.067 ml/100 ml blood/mmHg partial pressure.

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    Estimating PaO2

    Multiply inspired concentration by 5 to estimate PaO2 in mmHg.

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    Raoult's Law

    Vapor pressure of a component in a solution = vapor pressure of pure substance x its mole fraction.

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    Difference between Henry's and Raoult's Laws

    Henry's law addresses gas solubility in liquids; Raoult's law deals with vapor pressure in solutions.

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    Boiling Point Elevation

    The boiling point increases with solute concentration in a solution.

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    Freezing Point Depression

    The freezing point decreases when solutes are added to a solvent.

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    Diffusion

    The net movement of molecules from high to low concentration.

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    Graham’s Law

    Rate of gas diffusion is inversely proportional to the square root of its molecular weight.

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    Permeable Membrane

    Allows solvent and solute to pass through.

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    Osmosis

    Movement of water across a semipermeable membrane to balance solute concentrations.

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    Osmotic Pressure

    The pressure required to prevent osmosis in a solution.

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    Oncotic Pressure

    Osmotic pressure due to plasma proteins in capillaries.

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    Tonicity

    The relative concentration of solutes in two solutions.

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    Study Notes

    Henry's Law

    • Henry's Law relates gas solubility in a liquid to its partial pressure.

    • The amount of dissolved gas is directly proportional to the gas's partial pressure above the liquid. (p = kc, where p is pressure, k is Henry's constant, and c is concentration)

    • Used in anesthesia to calculate dissolved O2 and CO2 in blood.

    • Increasing the partial pressure (overpressurizing) of an anesthetic increases alveolar concentration, blood solubility, and uptake speed.

    • Oxygen Solubility: 0.003 ml O2 / 100 ml blood / mmHg partial pressure.

      • To find dissolved O2, multiply partial pressure by 0.003.
      • Example: PaO2 of 300 mmHg results in 0.9 ml O2 dissolved per 100 ml blood.
      • A rise in PaO2 from 100 mmHg to 500 mmHg increases dissolved O2 by 1.2 ml/100 ml blood.

    • Estimating PaO2 (inspired ml O2): Multiply inspired O2 concentration (FiO2) by 5.

    • Carbon Dioxide Solubility: 0.067 ml CO2 / 100 ml blood / mmHg partial pressure.

      • Example: PaCO2 of 50 mmHg results in 3.35 ml CO2 dissolved per 100 ml of blood.

    Raoult's Law

    • Raoult's Law describes vapor pressure of a volatile component in a solution.
    • Vapor pressure (P) of a component in a solution equals the vapor pressure of the pure substance (P°) multiplied by the mole fraction (χ) of that component. (P = χP°)
    • The presence of solute reduces the vapor pressure of the solution compared to the pure solvent.

    Colligative Properties

    • Colligative properties depend on the number of solute particles, not their type.
    • Vapor pressure, boiling point, freezing point, and osmotic pressure are all examples.

    Boiling Point Elevation

    • Boiling point is the temperature where vapor pressure equals ambient pressure.
    • Boiling point increases with increasing solute concentration.
    • The boiling point elevation is directly proportional to the molal concentration of solute.

    Freezing Point Depression

    • Freezing point is when liquid and solid phases are in equilibrium.
    • Solute particles hinder orderly crystal formation, requiring lower temperatures and thus decreased kinetic energy.
    • Addition of solute lowers the freezing point.

    Diffusion

    • Diffusion is the net movement of molecules to equalize concentration gradients.
    • Temperature (proportional to kinetic energy) and molecular weight affect speed.
    • Higher Kinetic Energy, faster diffusion.
    • Smaller molecules diffuse faster.

    Graham's Law

    • Graham's Law describes the relationship between diffusion rate and molecular weight.
    • Diffusion rate is inversely proportional to the square root of the molecular weight (r = 1/√mw).
    • Smaller molecules diffuse faster.

    Permeable/Semipermeable Membranes

    • Diffusion can occur through permeable membranes or open spaces.
    • Diffusion through membranes depends on concentration gradient, membrane area, solubility, membrane thickness, and molecular weight.

    Osmosis

    • Osmosis is the movement of water across a semipermeable membrane to equalize solute concentrations.
    • Tonicity refers to the relative solute concentrations in osmotic systems.
    • Isotonic solutions have equal solute concentrations.
    • Osmosis occurs until concentrations are equal.

    Osmotic Pressure

    • Osmotic pressure (Π) is the force to stop osmosis.

    • Oncotic pressure is the osmotic pressure exerted by plasma proteins & electrolytes.

    • It balances hydrostatic pressure, keeping fluid within capillaries.

    • Normal oncotic pressure is ~28 mmHg.

    Additional Notes

    • The vascular system acts as a semipermeable membrane that sequesters fluids.
    • Albumin (a large protein) is a major determinant of intravascular volume.
    • The major difference between Henry's and Raoult's laws is that Henry's law deals with gases dissolving in a solution, while Raoult's law deals with the vapor pressures of components in a mixed solution.

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    Description

    Explore the principles of Henry's Law and its application in anesthesia. This quiz covers the relationship between gas solubility in blood and partial pressure, including calculations for oxygen and carbon dioxide. Test your understanding of how these concepts affect anesthetic administration.

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