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CardioPulmonary Class > Diffusion and Gas Transport Lecture 5 > Flashcards

Diffusion and Gas Transport Lecture 5 Flashcards

1
Q

Identify factors that determine exchange rates of gases across membranes.

A
  1. Pressure difference - the gas between the two sides of the membrane
  2. Thickness - respiratory membrane
  3. Surface area - the membrane
  4. Diffusion coefficient - the gas in the substance of the membrane
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2
Q

Define Fick’s Law

A

Describes how particles under random thermal motion tend to spread form a region of higher concentration to a region of lower concentration. This law describes the time course of the transfer of a solute between two compartments that are seperated by a thin membrane.

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3
Q

Identify two factors which determine the concentration of a gas in a solution using Henry’s Law

A
  1. Partial pressure of gas
  2. Solubility coefficient
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4
Q

Compare solubility coefficients for oxygen, carbon dioxide, carbon monoxide, and nitrogen

A

O2 - 0.024

CO2 - 0.018

CO - 0.018

N - 0.012

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5
Q

Using Henry’s Law, calculate the amount of oxygen dissolved in blood for PO2 of 50, 100, and 600 mmHg

A

Concentration of dissolved gas = Partial pressure of gas x Solubility coefficient

Cgas= K x Pgas

K of oxygen dissolved in blood = 0.003

  • If PO2 is 100 mmHg – 0.003 x 100 = 0.3 mL O2/100 mL blood
  • If PO2 is 50 mmHg – 0.003 x 50 = 0.15 mL O2/ 100 mL blood
  • If PO2 is 600 mmHg – 0.003 x 600 = 1.8 mL O2/ 100 mL blood
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6
Q

Identify the mechanism responsible for most carriage of oxygen in the plasma

A
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7
Q

Describe the effects of increasing FiO2 from 100 to 600 mmHg on oxygen carrying capacity

A

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8
Q

Identify the average capillary exposure/transit time

A

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9
Q

Identify the normal time period required for diffusion to occur

A

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10
Q

Describe the effect of lower alveolar PO2 on diffusion and arterial PO2

A

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11
Q

Compare arterial and tissue PO2 and the effect on diffusion

A

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12
Q

Discuss the mechanism of diffusion of carbon dioxide across the alveolar septa

A
  • Carbon dioxide crosses the alveolar septa via simple diffusion based on a concentration gradient
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13
Q

Discuss the mechanism of diffusion of oxygen across the alveolar septa

A

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14
Q

Define Graham’s Law

A

When gases are dissolved in liquids, the relative rate of diffusion of a given gas (diffusion capacity) is

  • Proportional to solubility in the liquid
  • Inversely proportional to the suare root of its molecular weight
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15
Q

Compare the diffusion capacity of oxygen relative to carbon dioxide, nitrous oxide, carbon monoxide, and nitrogen

A

?

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16
Q

Describe the two major elements of diffusion capacity and their components

A
  1. Membrane capacity (DM)
    • Affected by factors involving movement of gas between alveoli and blood
  2. Reaction time with hemoglobin (O - VC)
    • Affected by factors involving movement into capillary and uptake by RBC
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17
Q

List four conditions that decrease diffusing capacity

A
  1. Thickening of the barrier
    • Interstitial or alveolar edema
    • Interstitial or alveolar fibrosis
      • Sarcoidosis
      • Scleroderma
  2. Decreased surface area
    • Emphysema
    • Tumors
    • Low cardiac output
    • Low pulmonary capillary blood volume
  3. Decreased uptake by erythrocytes
    • Anemia
    • Low pulmonary capillary blood volume
  4. Ventilation - perfusion mismatch
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18
Q

Calculate the amount of oxygen dissolved in the plasma given a PO2

A

*

19
Q

Identify the maximum amount of oxygen which may combine with a gram of hemoglobin

A
  • Maximum amount is 1.34 ml/gram of hemoglobin
20
Q

Identify the determinant of the equilibrium point of reaction that determines the amount of oxygen that binds to hemoglobin in the red blood cell.

A

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21
Q

Calculate oxygen content of the blood given hemoglobin concentration and oxygen saturation

A

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22
Q

Define P50 for hemoglobin saturation

A
  • Point on the curve where 50% saturation occurs
  • This point may move left or right, and represents changes in loading and unloading conditions
  • Affected by temperature, pH, PCO2, DPG levels and type of hemoglobin
23
Q

Calculate the oxygen carrying capacity for varying hemoglobin concentrations and PO2

A

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24
Q

Describe the structure of hemoglobin in relationship to its oxygen carrying capacity

A

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25
Q

Calculate delivery of oxygen given PaO2 and mixed venous PO2 (comparable to tissue PO2)

A

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26
Q

Describe rationale for monitoring SVO2

A

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27
Q

List five determinants of SVO2

A
  1. Hemoglobin concentration
  2. Hemoglobin saturation
  3. Cardiac output
  4. Oxygen consumption
  5. Oxygen utilization
28
Q

List six clinical conditions that may decrease SVO2

A
  1. Cardiac output
  2. Oxygen saturation/ ventilation/ shunt, V/Q
  3. Tissue metabolism
  4. Anesmia/ Hypovolemia
  5. Fever, shivering
  6. Seizures
  7. Pain/ Exercise
  8. Hyperthyroidism
29
Q

List five factors taht may alter P50 and how the oxygen-hemoglobin saturation curve is affected

A

1.

30
Q

Define the Bohr Effect as it relates to shifts in the oxyhemoglobin dissociation curve and oxygen loading/unloading

A

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31
Q

List four clinical conditions shifting the oxyhemoglobin dissociation curve to the left

A
  1. Decrease in H+ concentrations
  2. Decrease in PCO2
  3. Decrase in temperature
  4. Decrease in 2,3 BPG
    • Bank blood has decreased 2,3 BPG
    • High atitude and hypoxia cause increases in 2,3 BPG
  5. Fetal Hb (HbF)
  6. Carboxyhemoglobin
  7. Methemoglobin
32
Q

List four clinical conditions shifting the oxyhemoglobin dissociation curve to the right

A

RIGHTS

  1. Rightward shift
  2. Increased PCO2
  3. Increased 2,3 BPG
  4. Hydrogen Ions
  5. Temperature high
  6. Sickle cell
33
Q

Describe the effect of carbon monoxide poisoning on oxygen carrying capacity and the oxygen dissociation curve

A

*

34
Q

Discuss mechanisms for dealing with carbon monoxide poisoning

A
  • Carbon monoxide interferes with O2 transport by combining with Hb to form carboxyhemoglobin (COHb)
  • Hb concentration and PO2 are normal but O2 content is grossly reduced
  • Oxyhemoglobin dissociation curve shiftts to left
    • 210 x affinity for hgb as oxygen
  • Normal O2 saturation does not exclude possibility of carbon monoxide toxicity
  • Increased FiO2 promotes elimination of carbon monoxide (decreases half-life form 4 hours to < 1 hour)
35
Q

Discuss the pathophysiology of methemoglobinemia and clinical considerations.

A

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36
Q

Describe P50 considerations of abberant hemoglobin’s

A

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37
Q

List six anesthetic considerations for patients with sickle cell

A
  1. Avoid hypoxia and acidemia (FiO2 > 0.5)
  2. Avoid hypovolemia
  3. Avoid hypothermia
  4. Transfuse the preoperative PCV 30%
  5. No tourniquets
  6. Symptoms: Microvascular occlusions, cheast or abdominal pain, fever, tachycardia, hematuria.
38
Q

Describe how carbon dioxide is transported in the arterial and venous blood

A

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39
Q

Calculate the amount of CO2 dissolved in the blood given a PCO2

A

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40
Q

Compare the CO2 carrying capacity of reduced hemoglobin compared to oxyhemoglobin

A

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41
Q

Define the Haldane effect in relationship to the ability of hemoglobin to carry CO2

A

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42
Q

Define “Chloride shift” as it relates to RBC electrical neutrality and carbonic acid

A
  • More bicarb ions leave RBC than H+ ions
  • Hamburger shifts occurs and allows excess bicarbonate ions to diffuse out of cell in exchange for chloride ions (preserves electrical neutrality)
43
Q

Compare the carboxyhemoglobin dissociation curve to the oxyhemoglobin dissociation curve

A

*

CardioPulmonary Class (6 decks)

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