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FHB - Pulmonary & Renal - Exam 2 > Pulmonary 6 - Lecture 28 > Flashcards

Pulmonary 6 - Lecture 28 Flashcards

1
Q

What is the Bohr Equation?

What is the normal PaO2? PaCO2? PAaDO2?

A

(VD/Vt) = (PaCO2 – PeCO2) / PaCo2

PaO2 = 95 mmHg
PaCO2 = 40 mmHG

Difference of Alveolar & Arterial O2 is usually 5 mmHg

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2
Q

What is normal Ventilation?

A

V = f*Vt = 7.5 L/min

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3
Q

How is Flow of gas:blood as compared to VOLUME of gas:blood?

A

FLOW is about 1:1 (5250 in alveolar ventilation, and 5000 ml/min pulmonary blood flow)

VOLUME is disproportionate
43:1

(3000 ml/min in ALVEOLAR gas

& 70 ml of Pulmonary Capillary Flow)

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4
Q

What is the V/Q ratio at the level of a single alveolus? At the level of the whole lung?

A
  1. Alveolar Ventilation: Capillary FLow

2. Total Alveolar Ventilation: Cardiac Output

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5
Q

What is a normal V/Q ratio?

V/Q > 1 means what?
V/Q <1?

A

0.8

high V/Q means ventilation exceeds perfusion

low V/Q means perfusion exceeds ventilation

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6
Q

Describe the V/Q ratios of the following:
Does gas exchange occur?

  1. shunt Alveoli
  2. Normal (O2 = 100, CO2 = 40)
  3. Dead Space Alveolus
A 
1. SHUNT 
Perfused, but not ventilated
V/Q = 0
- NO GAS EXCHANGE
- PO2 and PCO2 match venous blood (40 & 45)
  1. V/Q = 1
    - gas exchange occurs
  2. Dead Space:
    V/Q = infinity
    Ventilated but not perfused

(Po2 and Pco2 approach level of inspired gas)
= NO GAS EXCHANGE

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7
Q

Describe the perfusion and ventilation in the following parts of the lung:

  1. Apex
  2. Middle
  3. Base
A
  1. Apex:

Ventilated, but little perfusion
V/Q >1

  1. Normal V/Q = 1
  2. Base:
    Perfused more than ventilated
    V/Q <1
  • distance up lung, drop in flow is GREATER than the drop in ventilation
    (even tho the apex receives the lowest percentage of ventilation & perfusion)
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8
Q

Why is the drop in blood flow greater than the drop in ventilation at the APEX?

A

Gravity has a greater impact on high density blood than on low density air

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9
Q

How is the PaO2 and PCO2 at the apex of the lung as compared to the middle regions of the lung? Base?

A

PaO2 is higher
and PCO2 is lower than in the middle regions

BASE:
PaO2 is lower, and PaCO2 is HIGHER than in middle

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10
Q

What spaces are “Over -ventilated”? Which are over-perfused?

A
  1. Apex - dead space units

2. Base - physiological shunt units that are “over-perfused”

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11
Q

Where does the majority of oxygenated blood leaving the lung come from?

A

BASE

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12
Q

What is flow in the apex and the base?WHat is ventilation in the apex and base?

A

APEX: –> V/Q = 3
V = 132
Flow/Q = 0.7

BASE: –> V/Q = 0.6
V = 89
Q= 3

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13
Q

What is the normal AaDO2 at room air?

A

less than 15 mmHg

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14
Q

When does AaDO2 rise?

A

Rises with AGE

Age in years/ 4 + 4

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15
Q

What are causes of hypoxemia? (4)

A
  1. Hypoventilation
  2. Diffusion Limitation
  3. Shunt
  4. Ventilation-Perfusion Mismach (V/Q inequality)
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16
Q

What is the Alveolar Gas Equation?

A

PAo2 = (PiO2 - PaCO2)/R

Pio2 = (Patm - Pwater)*Fio2

17
Q

What is hypoxia?

A

Deprivation of the whole body or specific organs and tissues of oxygen

  • usually oxygen supply & tissue demand NOT EQUAL
18
Q

What is hypoxemia?

A

When oxygen concentration in arterial blood is too low

19
Q

What is tissue anoxia?

A

If there is complete withdrawal of oxygen supply (during clot formation)

20
Q

What pressure of PO2 qualifies as HYPOXEMIA?

A

PO2 < 80 mmHg at sea level

21
Q

In hypoventilation, what does Alveolar PO2 depend on? (2)

A
  1. Rate of Removal from blood (metabolic demand)

2. Rate of replenishment of O2 by Alveolar Ventilation

22
Q

What happens to the following in Hypoventilation:

  1. Alveolar Po2
  2. Alveolar PCO2
  3. AaDO2

Possible Reasons?
How can we increase PaO2?

A
  1. Alveolar PO2 DECREASES
  2. Alveolar PCO2 increases
  3. AaDO2 does NOT change (NORMAL)
    - not enough O2 in, but the transfer of gas is completely normal!

Reasons: drugs that depress central drive to breath ( morphine, heroin, barbiturates)

Increase PaO2 by adding MORE O2!

  • if ventilation decreases 2 fold, CO2 increases 2 fold
23
Q

What are the reasons for Diffusion Limitation?

Is AaDO2 normal?

How can PaO2 be increased?

A
  1. Lung edema, fibrosis, alveolar capillary block (deposition of materials)
    - anything that decreases AREA or increases THICKNESS
  2. AaDO2 is INCREASED (diffusion of Arterial O2 is decreased since thicker membrane)
  3. Add additional O2 will increase PaO2
24
Q

What are the reasons for a SHUNT that causes hypoxemia?

Is AaDO2 normal?

How can PaO2 be increased?

A 
1.Anatomic Shunt - congenital heart disease (tretalogy of fallot)
Physiological shunt (mucous plug that clogs bronchi) (atelectasis)
  1. AaDO2 INCREASES (since the arterial blood Oxygen is not increasing)
  2. Adding additional O2 will NOT INCREASE PaO2 to the expected level
25
Q

What is the only form of Hypoxemia that does not increase PaO2 with increased O2? Does not rise to the expected level under 100% oxygen…

A

SHUNT!

  • blood that bypasses the ventilation will have the same oxygen concentration as venous blood
  • still have perfusion but NO VENTILATION
  • thus increasing O2 to 100% oxygen only shows a small increase in PaO2 due to the characteristics of Oxygen Binding Hb (s-shaped curve)
26
Q

What are the reasons for a Ventilation - Perfusion Inequality that causes hypoxemia? (PO2 <80 mmHg)

Is AaDO2 normal?

How can PaO2 be increased?

A
  1. mismatch of V/Q (low ratio means that perfusion is higher than ventilation)
  2. AaDO2 INCREASED
  3. PaO2 can be increased with additional O2!
27
Q

What is the most frequent reason for hypoxemia in patients with respiratory disorders?

A

Ventilation - Perfusion Inequality

28
Q

In ventilation - Perfusion inequality, will hyperventilation increase PaO2? What about PCO2 levels?

A

NO, hyperventilation will not decrease the V/Q inequality

  • elimination of CO2 is impaired, but CO2 CAN be eliminated by increasing alveolar ventilation!

WHY? linear relationship of pCO2 and PCO2 content in blood

29
Q

What is the Alveolar- Arterial PO2 difference most useful to assess?

A

Alveolar – arterial PO2 difference is useful to assess the cause for hypoxemia

30
Q

What is the only case of Hypoxemia that 100% of O2 will NOT increase the PaO2?

A

SHUNT!!

31
Q

What is the formula to calculate Alveolar VENTILATION?

A

Alveolar ventilation = (VT – VD) x RR; only part of your tidal volume is actually involved in alveolar ventilation

VT = Tidal volume
VD = Physiologic Dead Space
RR = Respiratory Rate

FHB - Pulmonary & Renal - Exam 2 (21 decks)

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