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module 103 - theme 4 > respiratory failure > Flashcards

respiratory failure Flashcards

1
Q

what is hypoxia?

A

reduced level of tissue oxygenation

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2
Q

what is hypoxaemia?

A

decrease in partial pressure of oxygen in the blood

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3
Q

why do hypoxia and hypoxaemia not always coexist?

A

individuals can develop hypoxaemia without hypoxia is there is a compensatory

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4
Q

what is arterial oxygen tension?

A

the partial pressure of oxygen that indicates the dissolved oxygen in plasma (not oxygen bound to Hb)

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5
Q

what measures hypoxia and hypoxaemia?

A

uses an arterial blood gas analyser

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6
Q

what law does pulse oximetry use?

A

Beer-Lambert-Bougeur law

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7
Q

what is type 1 respiratory failure?

A

reduction in PaO2 but no change in PaCO2 - V/Q mismatch

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8
Q

what is type 2 respiratory failure?

A

increase in PaCO2 and reduction in PaO2 - underventilation

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9
Q

what are the 5 mechanisms of hypoxaemia?

A

1) V/Q mismatch
2) right-to-left shunt
3) diffusion impairment
4) hypoventilation
5) low inspired pO2

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10
Q

what is the A-a gradient?

A

the difference between the alveolar O2 level and the arterial O2 level

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11
Q

what does the A-a gradient indicate?

A

the integrity of the alveolocapillary membrane and the effectiveness of gas exchange

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12
Q

if hypoxaemia has a widened A-a gradient what is it caused by?

A

V/Q mismatch, diffusion limitation and shunt

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13
Q

if hypoxaemia has a normal A-a gradient what is it caused by?

A

hypoventilation

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14
Q

what is the most common cause of hypoxemia?

A

V/Q mismatch

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15
Q

what is regional heterogeneity of V/Q?

A

sub atmospheric intrapleural pressure and gravity

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16
Q

how does V/Q mismatch cause hypoxaemia?

A
  • ventilation and perfusion are higher at the bases and lower at the apex
  • V/Q ratio is higher at the apex and low at the base
  • a low V/Q ratio produces hypoxemia by decreasing the PAO2 and subsequent PaO2
  • hypoxemia is caused if the compensatory rise in total ventilation is absent
17
Q

what is the compensatory mechanism of a V/Q mismatch?

A

there is a restriction in perfusion in areas of the lung with reduced ventilation known as hypoxic pulmonary vasoconstriction

18
Q

what are the characteristics of a V/Q mismatch?

A
  • hypoxaemia due to V/Q mismatch can easily be corrected by supplemental oxygen
  • widened A-a gradient
19
Q

what are the common causes of a V/Q mismatch?

A

asthma, COPD, bronchiectasis, cystic fibrosis, ILD and pulmonary hypertension

20
Q

what is a shunt?

A

blood from the right side of the heart enters the left side without taking part in case exchange

21
Q

what feature of a shunt distinguishes it from other mechanisms?

A

there is a poor response to oxygen therapy

22
Q

what fraction does the shunt have to reach for hypoxemia to be more common?

A

50%

23
Q

why is there a lack of hypercapnia in a shunt?

A

due to stimulation of the respiratory centre by chemoreceptors

24
Q

what are the characteristics of a pulmonary shunt?

A
  • A-a gradient is elevated
  • pCO2 is normal
  • poor response to oxygen therapy
25
Q

what are the common causes of a shunt?

A

pneumonia, pulmonary oedema, ARDS, pulmonary arteriovenous communication

26
Q

what is diffusion limitation?

A

transport across the alveolocapillary membrane is impaired due to a decrease in lung surface area for diffusion, inflammation and fibrosis, low alveolar oxygen and reduced capillary transit time

27
Q

why is hypercapnia uncommon with diffusion limitation?

A

CO2 is 20x more soluble in O2 and is less likely to be affected by diffusion limitation

28
Q

what are the characteristics of diffusion limitation?

A
  • hypoxaemia shows a good response to oxygen therapy
  • A-a gradient is elevated
  • PaCO2 is normal
29
Q

what is the hallmark of hypoventilation?

A

high PaCO2

30
Q

when does hypoventilation cause significant hypoxaemia?

A

in the presence of lung disease

31
Q

how do you correct hypoxaemia due to hyperventilation?

A

oxygen therapy however hypoventilation and hypercapnia can persist

32
Q

what are the causes of hypoventilation?

A
  • impaired central drive: drug overdose, brain stem infarction, primary alveolar hypoventilation
  • spinal chord: ALS
  • nerve: Guillan-Barre syndrome
  • neuromuscular junction: Myasthenia graves
  • respiratory muscles: myopathy
33
Q

what are the characteristics of hypoventilation?

A
  • hypoxaemia shows good response to oxygen therapy
  • A-a gradient is normal
  • PaCO2 is high

module 103 - theme 4 (19 decks)

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