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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
How doe obesity cause type 2 respiratory failure?
* Carry huge amount of weight on chest - cannot physically breathe * Abdomen full of fat - diaphragm cannot descend
26
Why are patients with type 2 respiratory failure sensitive to high concentrations of oxygen?
Develop hypercarbia, become acidotic very quickly
27
What makes patients retain CO2?
V/Q mismatching
28
Explain how how levels of oxygen leads to V/Q mismatching in patients with type 2 respiratory failure?
* Areas of poor ventilation have reactive vasoconstriction * Excess oxygen reverses vasoconstriction * Perfusion becomes good but ventilation is poor, resulting in CO2 retention
29
What is the haldene effect?
Removing O2 from Hb increases the ability of Hb to pick-up CO2 and CO2 generated H+
30
How does the Haldane Effect apply to chronically hypoxaemic patients?
CO2 occupies the empty binding sites on Hb (due to oxygen dissociation due to low PO2)
31
What happens if a high FiO2 is given to a chronically hypoxaemic patient?
Pushes CO2 off Hb into the system, resulting in increased PCO2
32
What is the relationship between hypoxia and the Haldane Effect?
The more hypoxic the patient, the larger the haldene effect will be and the greater the PCO2 levels in response to given oxygen
33
How does hypoxic drive occur?
* Normal respiration driven by CO2 chemoreceptors * Chronic hypercarbia leads to desenstisation of these receptors * Oxygen chemoreceptors then become important
34
Why is hypoxic drive important in delivery of oxygen?
Too much oxygen results in loss of hypoxic drive - reduction in respiratory effort leading to increased PCO2
35
How can chronically hypoxaemic patients without CO2 retention still become acidotic?
Due to Haldane Effect - increased PCO2
36
What are symptoms of hypoxaemia?
* Altered mental state * Cyanosis * Dyspnoea * Tachypneoa * Arrhythmia
37
What happens when PO2 < 5.3 kPa?
Hyperventilation increases dramatically
38
What happens when PO2 < 4.3 kPa?
Loss of consciousness
39
What happens when PO2 < 2.7 kPa?
Death
40
What is the best SaO2 for an individual with sepsis?
85%-95%
41
What is DO2?
Gobal oxygen delivery - the total amount of oxygen delivered to the tissues per minute
42
What is the equation for DO2?
DO2 = CO x [(1.3 x Hb x SaO2) + 0.003 x PaO2)]
43
What is DO2 dependent on?
Hb saturation - less about PaO2
44
What are different types/causes of hypoxia?
* Circulatory hypoxia * Anaemic hypoxia * Toxic hypoxia * Hypoxaemic hypoxia
45
What are causes of toxic hypoxia?
* Cyanide * Arsenic (prevent O2 release from Hb) * CO - binds irreversibly to Hb, oxygen not released to tissues
46
What causes hypoxaemic hypoxia?
* Low inspired oxygen concentration * Alveolar hypoventilation * Impaired diffusion * Shunt * Dead space * Ventilation perfusion mismatch
47
What causes low inspired oxygen concentration?
* Low FiO2 of anaesthetic gases | * Low barometric pressure at high altitudes
48
What are causes of hypoventilation?
* Opiates * Glottic swelling * Obesity
49
What are some causes of alveolar hypoventilation?
* Upper airway obstruction * Epiglottitis * Laryngospasm * Inhaled foreign body * Muscular weakness * Central respiratory suppression * Ondine’s Curse * Obesity hypoventilation * Opiate toxicity * Kyphoscoliosis
50
What are the causes of impaired diffusion?
* Interstitial thickening * Pulmonary fibrosis * Lymphangitis * Sarcoidosis * Vascular Dysfunction * Pulmonary vasculitis * Endothelial malignancy
51
What is shunting?
Perfusion without ventilation
52
What is dead space?
Ventilation without perfusion
53
What is a common cause of dead space?
Pulmonary embolus
54
What are some causes of shunting?
* Pulmonary oedema * Asthma * COPD * Sarcoidosis * Pulmonary eosinophilia * Bronchiectasis * Lung cancer * Asbestosis
55
What are the causes of dead space?
* Pulmonary embolism * Pulmonary vasculitis * Pulmonary hypertension
56
What is the V/Q ratio at the lung apex?
Good ventilation, poor perfusion
57
What is the V/Q ratio at the lung base?
Poor ventilation, good perfusion
58
What is oxygen used to treat?
Hypoxaemia
59
What is oxygen not used to treat?
Breathlessness
60
In what circumstances should patients be given all the oxygen?
* MI (previously, not currently) * Severe sepsis * Severe trauma * Anaphylaxis
61
When should SaO2 be maintained at 88-92%?
Patients who are at risk of chronic type 2 respiratory failure
62
What should SaO2 be maintained at in normal individuals/individuals with any other illness?
94-98%
63
What are the features of a variable performance mask?
* Cheap and simple * 5 - 15 l/min * Uncontrolled FiO2 * Unable to cope with high flow requirements
64
What are the features of a venturi mask?
* Fixed performance | * Flows of up to 250 l/min
65
What do the different colours of Venturi mean?
``` Blue - 24% White - 28% Orange - 31% Yellow - 35% Red - 40% Green - 60% ``` (big wet orange yells really grumpily)
66
What are the features of a non-rebreathing mask?
* Up to 85% FiO2 | * Uncontrolled FiO2

Fund Final (24 decks)

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