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Oxygen and respiratory failure Flashcards

1
Q

In what 2 ways is oxygen transported in the blood?

A
  • Bound to haemoglobin (98.5%)

* Dissolved in plasma (1.5%)

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2
Q

What is type 1 respiratory failure?

A

Short of oxygen (hypoxia) without increased CO2 (hypercapnia)

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3
Q

What is type 2 respiratory failure?

A

Short of oxygen (hypoxia) and increased CO2 (hypercapnia)

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4
Q

What diseases cause type 1 and type 2 respiratory failure?

A

No diseases cause type 1 and type 2 respiratory failure - it is all about physiology

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5
Q

What is the response to primary hypoxaemia in normal individuals?

A
  • Increase tidal volume (depth)
  • Increase respiratory rate
    (normal PO2, PCO2 lowered)
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6
Q

What is the response to primary hypoxaemia in individuals with poor lung function e.g. COPD?

A

Low PO2, normal PCO2

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7
Q

What happens if individuals with normal lung function and primary hypoxaemia get tired?

A

End up with type 1 respiratory failure (low PO2, normal PCO2)

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8
Q

What happens if individuals with normal lung function and primary hypoxaemia become extremely tired?

A

Results in hypoventilation - acute type 2 respiratory failure (low PO2, high PCO2 - respiratory acidosis)

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9
Q

What is the treatment for both type 1 and type 2 respiratory failure?

A

Oxygen

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10
Q

What is SaO2?

A

Oxygen saturation of arterial blood

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11
Q

What is SpO2?

A

Oxygen saturation as detected by the pulse oximeter (percutaneous oxygen saturation)

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12
Q

How is SpO2 measured?

A

With a pulse oximeter

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13
Q

Why is arterial blood bright red and venous blood dark red?

A
  • Oxygenated haemoglobin is bright red

* Deoxygenated haemoglobin is dark red

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14
Q

How does a pulse oximeter measure the percentage of oxygenated haemoglobin?

A

Measuring the ratio of infrared and red light

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15
Q

What is PaO2?

A

The amount of oxygen dissolved in blood plasma

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16
Q

Does the amount of oxygen bound to haemoglobin increase in proportion to partial pressure?

A

No, it increases as partial pressure of oxygen increases but not in proportion

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17
Q

What is the standard oxygen dissociation curve?

A

Plots PO2 against %HbO2 at a temperature of 37oC and pH 7.4

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18
Q

What is FiO2?

A

Fraction of Inspired Oxygen; it is the fraction of oxygen a patient is inhaling produced by an oxygen device such as a nasal cannula or mask

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19
Q

Why is it important to give controlled levels of oxygen rather than all the oxygen?

A

If giving huge amounts of oxygen, SATs will remain high despite a low PO2

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20
Q

Why should no one in hospital (unless under anaesthesia) have an oxygen saturation of over 98%?

A

Renders SATs completely useless

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21
Q

In which individual scout high levels of oxygen be poisonous?

A

Those at risk of type 2 respiratory failure

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22
Q

Why should SATs remain at 88% - 92% for individuals with COPD?

A

Type 2 respiratory failure - increased PO2 results in very high PCO2, causing acidosis

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23
Q

Why is acidosis dangerous?

A

Stops enzymes functioning

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24
Q

What are examples of people at risk of type 2 respiratory failure?

A
  • COPD
  • Kyphoscoliosis
  • Neuromuscular weakness (causes hypoventilation)
  • Obesity
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25
Q

How doe obesity cause type 2 respiratory failure?

A
  • Carry huge amount of weight on chest - cannot physically breathe
  • Abdomen full of fat - diaphragm cannot descend
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26
Q

Why are patients with type 2 respiratory failure sensitive to high concentrations of oxygen?

A

Develop hypercarbia, become acidotic very quickly

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27
Q

What makes patients retain CO2?

A

V/Q mismatching

28
Q

Explain how how levels of oxygen leads to V/Q mismatching in patients with type 2 respiratory failure?

A
  • Areas of poor ventilation have reactive vasoconstriction
  • Excess oxygen reverses vasoconstriction
  • Perfusion becomes good but ventilation is poor, resulting in CO2 retention
29
Q

What is the haldene effect?

A

Removing O2 from Hb increases
the ability of Hb to pick-up CO2 and
CO2 generated H+

30
Q

How does the Haldane Effect apply to chronically hypoxaemic patients?

A

CO2 occupies the empty binding sites on Hb (due to oxygen dissociation due to low PO2)

31
Q

What happens if a high FiO2 is given to a chronically hypoxaemic patient?

A

Pushes CO2 off Hb into the system, resulting in increased PCO2

32
Q

What is the relationship between hypoxia and the Haldane Effect?

A

The more hypoxic the patient, the larger the haldene effect will be and the greater the PCO2 levels in response to given oxygen

33
Q

How does hypoxic drive occur?

A
  • Normal respiration driven by CO2 chemoreceptors
  • Chronic hypercarbia leads to desenstisation of these receptors
  • Oxygen chemoreceptors then become important
34
Q

Why is hypoxic drive important in delivery of oxygen?

A

Too much oxygen results in loss of hypoxic drive - reduction in respiratory effort leading to increased PCO2

35
Q

How can chronically hypoxaemic patients without CO2 retention still become acidotic?

A

Due to Haldane Effect - increased PCO2

36
Q

What are symptoms of hypoxaemia?

A
  • Altered mental state
  • Cyanosis
  • Dyspnoea
  • Tachypneoa
  • Arrhythmia
37
Q

What happens when PO2 < 5.3 kPa?

A

Hyperventilation increases dramatically

38
Q

What happens when PO2 < 4.3 kPa?

A

Loss of consciousness

39
Q

What happens when PO2 < 2.7 kPa?

40
Q

What is the best SaO2 for an individual with sepsis?

41
Q

What is DO2?

A

Gobal oxygen delivery - the total amount of oxygen delivered to the tissues per minute

42
Q

What is the equation for DO2?

A

DO2 = CO x [(1.3 x Hb x SaO2) + 0.003 x PaO2)]

43
Q

What is DO2 dependent on?

A

Hb saturation - less about PaO2

44
Q

What are different types/causes of hypoxia?

A
  • Circulatory hypoxia
  • Anaemic hypoxia
  • Toxic hypoxia
  • Hypoxaemic hypoxia
45
Q

What are causes of toxic hypoxia?

A
  • Cyanide
  • Arsenic (prevent O2 release from Hb)
  • CO - binds irreversibly to Hb, oxygen not released to tissues
46
Q

What causes hypoxaemic hypoxia?

A
  • Low inspired oxygen concentration
  • Alveolar hypoventilation
  • Impaired diffusion
  • Shunt
  • Dead space
  • Ventilation perfusion mismatch
47
Q

What causes low inspired oxygen concentration?

A
  • Low FiO2 of anaesthetic gases

* Low barometric pressure at high altitudes

48
Q

What are causes of hypoventilation?

A
  • Opiates
  • Glottic swelling
  • Obesity
49
Q

What are some causes of alveolar hypoventilation?

A
  • Upper airway obstruction
  • Epiglottitis
  • Laryngospasm
  • Inhaled foreign body
  • Muscular weakness
  • Central respiratory suppression
  • Ondine’s Curse
  • Obesity hypoventilation
  • Opiate toxicity
  • Kyphoscoliosis
50
Q

What are the causes of impaired diffusion?

A
  • Interstitial thickening
  • Pulmonary fibrosis
  • Lymphangitis
  • Sarcoidosis
  • Vascular Dysfunction
  • Pulmonary vasculitis
  • Endothelial malignancy
51
Q

What is shunting?

A

Perfusion without ventilation

52
Q

What is dead space?

A

Ventilation without perfusion

53
Q

What is a common cause of dead space?

A

Pulmonary embolus

54
Q

What are some causes of shunting?

A
  • Pulmonary oedema
  • Asthma
  • COPD
  • Sarcoidosis
  • Pulmonary eosinophilia
  • Bronchiectasis
  • Lung cancer
  • Asbestosis
55
Q

What are the causes of dead space?

A
  • Pulmonary embolism
  • Pulmonary vasculitis
  • Pulmonary hypertension
56
Q

What is the V/Q ratio at the lung apex?

A

Good ventilation, poor perfusion

57
Q

What is the V/Q ratio at the lung base?

A

Poor ventilation, good perfusion

58
Q

What is oxygen used to treat?

A

Hypoxaemia

59
Q

What is oxygen not used to treat?

A

Breathlessness

60
Q

In what circumstances should patients be given all the oxygen?

A
  • MI (previously, not currently)
  • Severe sepsis
  • Severe trauma
  • Anaphylaxis
61
Q

When should SaO2 be maintained at 88-92%?

A

Patients who are at risk of chronic type 2 respiratory failure

62
Q

What should SaO2 be maintained at in normal individuals/individuals with any other illness?

63
Q

What are the features of a variable performance mask?

A
  • Cheap and simple
  • 5 - 15 l/min
  • Uncontrolled FiO2
  • Unable to cope with high flow requirements
64
Q

What are the features of a venturi mask?

A
  • Fixed performance

* Flows of up to 250 l/min

65
Q

What do the different colours of Venturi mean?

A 
Blue - 24%
White - 28%
Orange - 31%
Yellow - 35%
Red - 40%
Green - 60%

(big wet orange yells really grumpily)

66
Q

What are the features of a non-rebreathing mask?

A
  • Up to 85% FiO2

* Uncontrolled FiO2

Fund Final (24 decks)

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