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Anesthesia and Analgesia > Chapter 2- The respiratory system > Flashcards

Chapter 2- The respiratory system Flashcards

1
Q

What is minute ventilation?

A

Vmin is the volume of air breathed per minute

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2
Q

What determines ventilation?

A

The Tidal volume (VT) and the respiratory frequency
Vmin= VT x frequency

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3
Q

What is another name for the conducting airways?

A

Anatomical dead space

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4
Q

True/False: There is no gas exchange in the conducting airways (dead space)

A

True

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5
Q

What can increase mechanical dead space during anesthesia?

A

An excessively long endotracheal tube or a large face mask

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6
Q

What provides the energy during inhalation?

A

The respiratory muscles

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7
Q

What provides the energy during exhalation?

A

The elastic force stored in the stretched lung and thorax

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8
Q

Inhalation is ____ while exhalation is ____ process

A

An active process; a passive process

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9
Q

What happens with the intraabdominal pressure during diaphragm contraction?

A

The intraabdominal pressure increases

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10
Q

Why can the diaphragm function be altered during recumbency?

A

Because the abdominal viscera is stretching the diaphragm beyond optimal length

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11
Q

What do the external intercostal muscles do?

A

Move the ribs outward and forward

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12
Q

What do the sternohyoid and sternocephalic muscles do during strenuous breathing?

A

They move the sternum rostrally

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13
Q

What do the abdominal and internal intercostal muscles do?

A

Expiratory muscles

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14
Q

How does contraction of the internal intercostal muscles decrease the size of the thorax?

A

Moves the ribs caudally and downward

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15
Q

Define functional residual capacity (FRC)?

A

Is the residual volume of air after expiration

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16
Q

What is the FRC in horses?

A

45mL/kg

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17
Q

What happens during inhalation with the pleural pressure (numbers also)?

A

It decreases from -5 cm H2O to -10 cm H2O

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18
Q

Why are higher pressures needed to ventilate the horse during respiratory disease?

A

Because the disease can change resistance and elasticity and increase the work of breathing

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19
Q

What is pressure-volume hysteresis?

A

Is the difference between the pressure that takes to re-inflate the lungs and the pressure that is needed to maintain a certain pressure during deflation

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20
Q

Why is the hysteresis higher during anesthesia?

A

Because FRC decreases and airways might close, increasing the pressure needed to re-inflate

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21
Q

What is surfactant?

A

Is a combination of lipids and proteins that facilitate surfactant recruitment to the alveolar surface

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22
Q

What does surfactant do?

A

Reduces surface tension on the alveolar lining fluid

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23
Q

Who produces surfactant?

A

Type II alveolar cells

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24
Q

How does a conscious animal reactivate surfactant?

A

By sighing and expanding alveolar surface several times per hour

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25
Q

What can reduce the activation of surfactant?

A
  1. Anesthesia
  2. Chest pain
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26
Q

The nasal cavity, pharynx, and larynx provide ____ of the frictional resistance to breathing

A

50-70%

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27
Q

The trachea, bronchi and bronchioles provide the remaining ____ of the resistance divided in this way

A

30-50% divided in trachea 40%, bronchi 40% and bronchioles 20%

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28
Q

What produces the lung sounds perceived with the sthetoscope?

A

High velocity, turbulent airflow in trachea and bronchi

29
Q

What effect does the parasympathetic (vagal) stimulation have in the airways, specially which structure?

A

It narrows it, specially bronchi

30
Q

True/False: Intrapulmonary smooth muscle has a high concentration of sympathetic innervation

A

False

31
Q

How does relaxation of the smooth muscles happen in the airways?

A

Activation of Alpha-2-adrenoceptors by epinephrine released from the adrenal medulla

32
Q

What is the effect of volatile anesthetics in the airways, why?

A

Bronchodilation by relaxing airway smooth muscle

33
Q

How do inhalant anesthetics, IV anesthetics, and benzodiazepines decrease airway smooth muscle tone?

A

By reducing Ca influx through voltage-dependent Ca channels

34
Q

Why does dynamic compression happen?

A

When pressure surrounding the airway is higher than pressure within the airway

35
Q

Why is contraction of the abductor muscles necessary to avoid collapse in nares, pharynx, and larynx during inhalation?

A

Because pressure within airways is subatmospheric and is surrounded by atmospheric pressure

36
Q

Why are heavily sedated or anesthetized horses more prone to collapse of the nares, pharynx or larynx?

A

Because anesthesia reduces the tone of the abductor muscles

37
Q

When can intrathoracic dynamic collapse happen?

A

When the intrapleural pressure exceeds the intraluminal pressure (obstructive lung disease)

38
Q

True/False: High pressures are needed to reopen closed airways in the lung of an anesthetized horse.

A

True

39
Q

What does a decrease in FRC lead to, why?

A

Hypoxemia, presumably due airway closure that leads to uneven distribution of ventilation and V/Q inequalities

40
Q

True/False: Pulmonary circulation has low vascular resistance

A

True

41
Q

Where is blood flow distributed preferentially in an anesthetized horse, independently from the recumbency?

A

To the caudal-most portion of the caudal lobe of the lung

42
Q

Why horses anesthetized with halothane, enflurane and isoflurane are less effective at redistributing blood flow to better oxygenated regions of the lung?

A

Because a dose-dependent decrease of the Hypoxic pulmonary vasoconstrictor phenomenon

43
Q

Why do PPV and PEEP decrease CO?

A

By decreasing venous return due to increased intrathoracic pressure

44
Q

True/False: Air has 21% oxygen everywhere, the partial pressure changes with altitude

A

True

45
Q

Mixing of gases and exchange of O2 with CO2 occurs by ____

A

Diffusion

46
Q

What can affect the rate of diffusion? (4)

A
  1. The area available for diffusion
  2. Thickness of the air-blood area
  3. Physical properties of the gas
  4. Driving pressure gradient between alveolus and capillary blood
47
Q

Why does blood progressively rises its oxygen partial pressure (Driving pressure gradient)?

A

Alveolar PO2 = avg 100 mmHg
Venous PO2 = ~40 mmHg
Driving pressure gradient 60 mmHg causes rapid diffusion of O2 into the capillary

48
Q

What does Hb do during the oxygen diffusion?

A

It helps maintain the pressure gradient

49
Q

How long does it take for equilibration to happen?

A

0.25 seconds

50
Q

What can increase the driving pressure gradient?

A

Increasing the amount of oxygen that the horse is breathing (During anesthesia can be 100%)

51
Q

CO2 is ____ times more diffusible than O2 because of its higher solubility

A

20 times

52
Q

What is V/Q match, why is it important?

A

Is the matching of ventilation to blood flow, is the most important determinant of gas exchange

53
Q

What happens with V/Q in regions that receive reduced amount of ventilation, but continue to receive blood flow?

A

Those regions will have a low V/Q having a high CO2 content

54
Q

What happens with V/Q in areas of atelectasis (right-to-left shunt)?

A

That V/Q =0

55
Q

What happens with the blood in the areas of atelectasis?

A

Shunted blood does not participate of gas exchange

56
Q

What can happen when blood that did not participate on the gas exchange mixes with oxygenated blood?

A

It will cause hypoxemia

57
Q

What determines the magnitude of hypoxemia during right-to-left shunt?

A

The size of the shunt blood flow

58
Q

What can cause an elevated V/Q match?

A

Decreased pulmonary flow

59
Q

What does the Bohr equation calculate?

A

The amount of wasted ventilation (VD/VT)
VD/VT=(PaCO2-PECO2)/PaCO2

60
Q

V/Q relationships and consequences (TABLE)

A
61
Q

True/False: Gas exchange impairments result from blood flow to regions of the lung that are not ventilated rather than blood flow to regions served by intermittently closed airways

A

True

62
Q

How can Right-to-Left shunts be reduced?

A

By selective mechanical ventilation

63
Q

True/False: Gas exchange problems are more common when dissociative anesthetics are used during field anesthesia

A

False, hypoventilation does not occur

64
Q

What can the presence of pure oxygen (100%) cause in the alveoli?

A

Right-to-left shunting due to absorption atelectasis

65
Q

Why is PACO2 rarely affected by diffusion abnormalities, V/Q mismatch or right-to-left shunts?

A

Because hypoxemia stimulates ventilation

66
Q

Each molecule in the hemoglobin can bind to ____ molecules of oxygen reversibly

A

4 molecules of oxygen

67
Q

When leaving the lungs, Hb is saturated to ____, mixed venous blood is ____ saturated with oxygen when P)2 is 40 mm Hg.

A

95%; 75%

68
Q

A left shift in the Hb-oxygen dissociation curve will make release of oxygen into tissues ____

A

Slower

Anesthesia and Analgesia (4 decks)

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