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Anaesthetic FRCA Primary > Basic Sciences - Respiratory Physiology > Flashcards

Basic Sciences - Respiratory Physiology Flashcards

1
Q

SI unit for airway pressure

A

cm H2O

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2
Q

SI unit for partial pressure of gas

A

kPa

(kilo Pascal)

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3
Q

Definition of cm H2O / mmHg

A

Equivalent pressure exerted by a column of fluid of a given height, being acted on by gravity

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4
Q

kPa equivalent to 1 Atmosphere at sea level

A

101

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5
Q

cm H2O equivalent to 1 Atmosphere at sea level

A

1030

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6
Q

m H2O equivalent to 1 Atmosphere at sea level

A

10

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7
Q

mmHg equivalent to 1 Atmosphere at sea level

A

760

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8
Q

Approximate oxygen requirement increase during exercise

A

Up to 10x increased

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9
Q

Alveolar surface area for gas exchange in adults

A

80-90 metres squared

Approx half singles tennis court

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10
Q

Approx tidal volume in adults

A

6-8 ml/kg

Approx 500ml

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11
Q

Anatomical dead space approximate volume

A

150 ml

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12
Q

Alveolar ventilation approximate volume

A

350 ml

(Tidal volume - Anatomical dead space)

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13
Q

Minute ventilation calculation

A

Minute ventilation = Tidal volume x RR

Eg. 500 x 14 = 7000 ml/min

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14
Q

Alveolar minute ventilation calculation

A

Alveolar minute ventilation = Alveolar ventilation x RR

Eg. 350 x 14 = 4900 ml/min

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15
Q

Spirometry trace and volume terms

A

Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Vital capacity
Total lung capacity
Residual volume
Functional residual volume

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16
Q

Approximate inspiratory reserve volume for young fit male

A

3 L

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17
Q

Approximate expiratory reserve volume for young fit male

A

1.5 L

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18
Q

Approximate residual volume for young fit male

A

1 L

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19
Q

Approximate total lung capacity volume for young fit male

A

6 L

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20
Q

Approximate vital capacity volume for young fit male

A

5 L

21
Q

Approximate functional residual capacity volume for young fit male

A

2.5 L

22
Q

Functional residual capacity definition

A

Quantity of gas in the lungs at end of normal expiration

23
Q

Why functional residual capacity is important in anaesthetics

A

Provides oxygen reservoir during apnoea

FRC influences distribution of ventilation within lung by determining starting position of each lung area on the compliance curve

24
Q

Factors which reduce functional residual capacity

A

Reduced muscle tone:
- General anaesthesia

Increased intrathoracic pressure:
- Supine from standing
- Obesity
- Pregnancy

25
Q

Negative pressure generated during inspiration in alveoli

A

Around 2 to 3 cm H2O below atmospheric pressure

26
Q

What generates positive pressure during expiration in alveoli

A

Elastic recoil of lungs and chest wall

27
Q

Dominant muscle contributor during quiet breathing

A

Diaphragm > intercostal muscles

28
Q

How does Intermittent Positive Pressure Ventilation generate respiration

A

Increases pressure at mouth to create pressure gradient

29
Q

Approximate pressures usually required during IPPV to deliver same tidal volume as normal breathing

A

Higher pressures needed

Around 10 to 15 cm H2O

30
Q

Undesirable effect of IPPV on circulation

A
  • Increase in mean intrathoracic pressure
  • Reduces venous return to heart
  • Fall in cardiac output

Similar effect to Valsalva Manoeuvre

31
Q

Location of respiratory centres

A

Medulla and Pons

32
Q

Description of respiratory centres

A

Groups of neurons which act together to control respiration

33
Q

Factors which impact respiratory centres

A

Central chemoreceptors (increase in CO2)
Peripheral chemoreceptors (decrease in O2)
Cortex (volume control)
Stretch receptors (muscle activity)

34
Q

Most important factor in controlling respiration and reference range

A

Arterial PaCO2

Usually kept between 5.1 and 5.5

35
Q

CO2 response curve

A

As arterial PaCO2 rises, Minute ventilation increases

Lower end of curve flattens as automatic firing of respiratory centre maintains minimum minute ventilation

36
Q

Effect of opioids and GA on CO2 response curve

A

Depress CNS and make chemoreceptors less sensitive to PaCO2

Curve shifts to right and becomes less steep

37
Q

Two factors which need to be overcome for gas to reach the alveoli

A

Resistance (obstructive airway disease)

Compliance (restrictive lung disease)

38
Q

Compliance curve

A

Initial part of curve - high pressures needed to inflate alveoli from collapsed state

Once inflated lungs become compliant until chest wall reaches limit of expansion

39
Q

Forces involved in expiration

A

Passive process usually

Energy used to overcome compliance in inspiration is stored as potential energy in the elastic tissues

This energy used to generate pressure gradient for expiration

40
Q

Distribution of ventilation in the lungs in normal patient breathing spontaneously at rest

A

Apices more expanded than bases
Therefore greater compliance at bases and mid zone of lungs
Bases and mid zones receive greater ventilation

41
Q

Distribution of perfusion in the lungs in normal patient breathing spontaneously at rest

A

Due to gravity, perfusion pressure reduces by 1 cmH2O for every cm in height above heart level, and increases by 1 cmH2O for every cm below heart level

42
Q

Ventilation / Perfusion matching in lungs (V/Q)

A

Both ventilation and perfusion are greater towards bases of lungs

Therefore ventilation and perfusion are well matched

43
Q

Definition of shunt

A

Area of lung becomes occluded (airway closure or secretions)

No ventilation to this area of lung

44
Q

Effect of a lung shunt

A

Unoxygenated blood mixes with blood from ventilated blood to give arterial hypoxaemia

Increasing inspired O2 will not correct hypoxaemia as area not ventilated

Need to clear obstruction

45
Q

Definition of alveolar dead space

A

Perfusion ceases due to occlusion (thrombus or air or drop in cardiac output)

No perfusion to ventilated area

46
Q

Effect of alveolar dead space

A

Drop in end tidal CO2

Gas not involved in respiratory exchange dilutes CO2 concentration from rest of lung gas

47
Q

Treatment of incomplete alveolar obstruction

A

Increase FiO2 as some ventilation occurs so aim to increase O2 in alveoli for gas exchange

48
Q

How does general anaesthesia produce a degree of V/Q mismatch

A
  • Fall in FRC
  • Lung moves down compliance curve
  • Lung bases have less ventilation
  • Perfusion distribution unchanged as gravity influenced

Results in V/Q mismatch

Anaesthetic FRCA Primary (48 decks)

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