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Respiratory > Week 5 - Hypoxia and respiratory failure > Flashcards

Week 5 - Hypoxia and respiratory failure Flashcards

1
Q

What level of O2 saturation is considered hypoxia?

A

-below 94%

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2
Q

When does tissue damage begin to occur?

A

-Below 90%

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3
Q

What two ways can you measure Hb saturation?

A
  • Pulse oximetry

- ABG

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4
Q

What are the 4 types of hypoxia?

A
  • Hypoxaemic -> low o2
  • Anaemic -> Low available Hb
  • Circulatory ->reduced delivery
  • Cytotoxic -> Inable to utilise
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5
Q

What is the status of pO2 and pCO2 in type 1 resp failure?

A

-Low pO2 with normal/low pCO2

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6
Q

What is the status of pO2 and pCO2 in type 2 resp failure?

A

-Low pO2 with high pCO2

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7
Q

What are the three mechanisms of resipratory failure?

A
  • Ventilation failure
  • Poor diffusion
  • Mismatch of ventilation and perfusion
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8
Q

What type of respiratory failure is caused by ventilation failure?

A

-Type 2

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9
Q

What disturbance in acid-base balance often accompanies type 2 resp failure?

A

-Respiratory acidosis

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10
Q

What is the most common cause of hypercapnia in ventilatory failure?

A

-Hypoventilation

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11
Q

What is the physiological mechanism behind type 2 resp failure leading to acidosis?

A
  • high pCO2 detected by central chemoreceptors
  • Low O2 detected by peripheral chemoreceptors
  • Stimulates breathing but there is ventilation failure so isnt corrected
  • Poor ventilation prevents full compensation
  • Respiratory acidosis
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12
Q

What are the 3 major catagories of ventilatory failure?

A
  • Poor respiratory effort
  • Chest wall deformities
  • Hard to ventilate lungs
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13
Q

Give examples of things causing poor respiratory effort leading to type 2 resp failure

A
  • Respiratory centre depression -> Narcotics/head injury

- Muscle weakness -> problems anywhere along neurological pathway from resp centre to muscles

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14
Q

Give examples of things causing chest wall problems leading to type 2 resp failure

A
  • Scoliosis/Kyphosis -> reduces chest expansion
  • Trauma
  • Pneumothorax
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15
Q

What is flail chest?

A

-Rib fractures which are broken in 2 places -> loose bit of chest wall independent of rest -> as you breath in and pressure becomes negative, flail segment sucked in and prevents expansion

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16
Q

Give examples of things causing hard to ventilate lungs leading to type 2 resp failure

A
  • Stiff lungs -> very severe fibrosis

- High airway resistance -> asthma, COPD

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17
Q

What type of respiratory failure is caused by diffusion defects and why?

A
  • Type 1

- CO2 not affected as it is so soluble it can still diffuse

18
Q

Why might CO2 be low in type 1 resp failure?

A
  • Hypoxia stimulates peripheral chemoreceptors

- Hyperventilation occurs and more CO2 blown off

19
Q

Give 3 examples of diffusion impairment

A
  • Fibrotic lung disease
  • Emphysema
  • Pulmonary oedema
20
Q

Why does diffuse lung fibrosis make diffusion difficult?

A

-Fibrous tissue in interstitial space between alveolus and capillary BM -> increased diffusion distance

21
Q

What type of pattern does fibrosis show on a spirometer?

A

-Restrictive

22
Q

How does emphysema cause diffusion difficulty?

A
  • Loss of elastin
  • Reduced recoil causes dilation of air spaces
  • Reduced surface area
23
Q

Why does barrel chest occur in COPD?

A

-Hyperinflation as alveoli lost recoil and become dilated, in addition to airway resistance increasing much earlier on expiration so air becomes trapped in chest

24
Q

Why is compliance said to increase in emphysema?

A
  • Loss of elastic
  • Loss of recoil
  • Lungs are easier to inflate
25
Q

What type of resp failure is caused by ventilation-perfusion mismatch?

A

-Type 1

26
Q

What is hypoxic vasocontriction?

A

-Lack of oxygen to capillaries around poorly ventilated alveoli causes vasoconstriction of these vessels in order to divert blood to those areas which are well ventilated

27
Q

Why does hypoxic vasoconstriction not fully compensate for poor ventilation? Why does this cause a low pCO2?

A

-The poorly ventilated areas are still perfused as cannot shut off completely -> the blood coming from these areas is hypoxic and causes hyperventilation via peripheral chemoreceptors -> more pCO2 blown off but cannot increase O2 uptake

28
Q

Name and explain a cause of poor perfusion causing V/Q mismatch

A
  • Pulmonary embolus
  • part of pulmonary circulation obstructed -> blood diverted to other parts of lung
  • No problem with ventilation so ventilation of affected parts wasted
  • Ventilation of healthy parts cannot match its perfusion and so you get a mismatch
29
Q

Give 3 examples of causes of poor ventilation in the lungs

A
  • Pneumonia
  • Acute asthma/COPD
  • RDS of newborn
  • Mucus plug
30
Q

Why is CO2 not affected in V/Q mismatch?

A

-The hypoxia causes peripheral chemoreceptors to increase breathing and thus more CO2 is blown off

31
Q

In general, in which type of resp failure should oxygen be used? Why?

A
  • Type 1
  • In diffusion defects it increases the concentration gradient to drive diffusion of O2
  • In V/Q mismatch it increases O2 uptake in uneffected areas
32
Q

How do you treat type 2 resp failure?

A

-Assisted ventilation

33
Q

Why do you get confusion in hypoxia?

A

-Cerebral hypoxia

34
Q

What is the difference in central and peripheral cyanosis?

A
  • Central -> increased de-oxyHb in blood -> present with peripheral
  • Peripheral -> poor perfusion -> can occur independent of central
35
Q

In chronic hypoxia, why does oxygen delivery increase?

A
  • Elevated Hb levels due to increased EPO stimulated by hypoxia
  • Increased 2,3 BPG in cells favours T state so oxygen given up more easily
36
Q

What is the result of chronic hypoxic vasoconstriction?

A
  • Pulmonary hypertension
  • Cor pulmonale
  • Right heart failure
37
Q

What is the most common type 2 respiratory failure?

A

-COPD (ventilation defect due to high airway resistance)

38
Q

What are two signs of hypercapnia?

A
  • Warm hands

- Flapping tremors

39
Q

Why is respiration driven by hypoxia in COPD patients with CO2 retention?

A

-chronic CO2 retention -> CSF acidity detected by central chemoreceptors -> Choroid plexus stimulated to pump HCO3- into CSF -> CSF returns to normal pH -> central chemoreceptors reset to that pCO2 -> no effect on respiration -> respiration now driven by peripheral chemoreceptors detecting hypoxia

40
Q

What is an acute exacerbation in COPD?

A

-Acute worsening of the resp failure needing treatment

41
Q

Why do you have to be careful giving high flow O2 to COPD patients whom retain CO2? What do you use instead?

A
  • Hypoxia drives respiration -> correction of hypoxia may reduce ventilation
  • Reducing Hypoxic vasoconstriction in poorly ventilated areas will worsen V/Q mismatch
  • Titrated o2 therapy with monitoring

Respiratory (17 decks)

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