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TAS Emergencies and Critical Care ✅ > Respiratory Support ✅ > Flashcards

Respiratory Support ✅ Flashcards

1
Q

What is respiratory failure defined as?

A

A syndrome of inadequate gas exchange

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2
Q

What is the result of the inadequate gas exchange in respiratory failure?

A

Arterial oxygen, carbon dioxide, or both cannot be maintained within their normal ranges

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3
Q

What is the normal oxygen PaO2?

A

> 11kPa

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4
Q

What is the normal carbon dioxide PaCO2?

A

<6.0kPa

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5
Q

What is the normal arterial-alveolar oxygen tension difference PA-aO2?

A

10-25mmHg (in room air)

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6
Q

What is a drop in arterial oxygenation termed?

A

Hypoxaemia

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7
Q

What is a rise in arterial carbon dioxide levels termed?

A

Hypercapnia

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8
Q

What determines the classification of respiratory failure into type I and II?

A

Absence or presence of hypercapnia respectively

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9
Q

What is type 1 respiratory failure defined as?

A

Hypoxia without hypercapnia (PaCO2 may be normal or low)

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10
Q

What is type 1 respiratory failure typically caused by?

A

V/Q mismatch

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11
Q

What is meant by V/Q mismatch?

A

The volume of air flowing in and out of the lungs is not matched with the flow of blood to the lungs

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12
Q

What categories of conditions can cause type 1 respiratory failure?

A
  • Parenchymal diseases
  • Interstitial lung diseases
  • Shunts
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13
Q

Give 3 interstitial lung diseases that can cause type 1 respiratory failure?

A
  • ARDS
  • Pneumonia
  • Emphysema
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14
Q

What kind of shunt can cause type 1 respiratory failure?

A

Right to left shunt

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15
Q

What is type 2 respiratory failure defined as?

A

Hypoxia with hypercapnia

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16
Q

What is the mechanism of type 2 respiratory failure?

A

Inadequate ventilation

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17
Q

What are the categories of causes of type 2 respiratory failure?

A
  • Increased airway resistance
  • Neurological hypoventilation
  • Neuromuscular problems
  • Decreased functional residual capacity
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18
Q

Give 3 causes of increased airway resistance

A
  • Croup
  • Bronchiolitis
  • Asthma
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19
Q

Give 2 causes of neurological hypoventilation

A
  • Drug effects

- Brain stem lesions

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20
Q

Give 2 neuromuscular problems causing type 2 respiratory failure

A
  • Guillain-Barre syndrome

- Congenital myopathy

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21
Q

Give 4 causes of reduced functional residual capacity

A
  • Kyphoscoliosis
  • Chest deformity
  • Pneumothorax
  • Flail chest
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22
Q

What can respiratory failure lead to if untreated?

A

End organ damage and death from hypoxia

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23
Q

What is the purpose of respiratory support in respiratory failure?

A

To prevent progression to organ damage and death, and maintain life while the underlying condition is treated

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24
Q

What does respiratory support range from?

A

Oxygen by face mask, to non-invasive support, endotracheal intubation and mechanical ventilation, and extracorporeal membrane oxygenation (ECMO)

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25
Q

Which children should receive oxygen support?

A

Children with SpO2 <92% in air

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26
Q

What happens at a SpO2 below 92%?

A

The oxygen haemoglobin dissociation curve becomes steep, and delivery of oxygen to the tissues becomes compromised

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27
Q

What can high concentration inspired oxygen cause?

A

Direct cellular toxicity and reabsorption atelectasis

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28
Q

What is the result of both high and low oxygen concentrations being damaging?

A

The amount of inspired oxygen should be titrated according to pulse oximetry

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29
Q

What does a fixed performance, high flow mask provide?

A

Fractional inspired oxygen concentration (FiO2) within range of 0.26-0.6

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30
Q

When might the FiO2 not be known?

A

With the more common variable performance masks, or with nasal cannulae

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31
Q

What FiO2 is usually provided with variable performance masks/nasal cannulae?

A

<0.4

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32
Q

What is the maximum FiO2 via face mask?

A

0.6

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33
Q

When can the FiO2 via face mask be increased above 0.6?

A

If reservoir bag is used

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34
Q

What FiO2 will be delivered using high flow oxygen (15L/min) delivered by face mask with reservoir bag?

A

Up to 0.9

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35
Q

What are the main indications for intubation and ventilation in respiratory failure?

A
  • Severe respiratory distress
  • Tiring due to excessive work of breathing
  • Progressive hypoxaemia
  • Reduced conscious level
  • Progressive neuromuscular weakness, e.g. Guillain-Barre syndrome
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36
Q

What are the methods of delivering non-invasive ventilation?

A
  • Tight fitting face mask
  • Nasal masks
  • Prongs
  • Hood
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37
Q

What is the main advantage of NIV?

A

Endotracheal intubation can be avoided, along with the complications of mechanical ventilation

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38
Q

Give an example of a complication of mechanical ventilation

A

Ventilator-associated pneumonia

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39
Q

What are the two main modalities of NIV?

A

CPAP and BiPAP

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40
Q

What does CPAP stand for?

A

Continuous positive airway pressure (CPAP)

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41
Q

What pressure is used for CPAP?

A

+5 to +10cm H20

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42
Q

What are the beneficial effects of CPAP?

A
  • Reduced alveolar collapse
  • Improved oxygenation via alveolar recruitment
  • Reduced work of breathing
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43
Q

What are the disadvantages of CPAP?

A
  • Skin necrosis at interface between face mask and skin
  • Stomach distention
  • Risk of aspiration
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44
Q

What does BiPAP stand for?

A

Biphasic positive airways pressure

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45
Q

What is BiPAP?

A

A mode of ventilation where two levels of pressure are set - inspiratory pressure (IPAP) and expiratory pressure (EPAP)

46
Q

What do most modern BiPAP ventilators allow?

A

The patient to breathe spontaneously

47
Q

How do BiPAP ventilators allow the patient to breathe spontaneously?

A

By detecting inspiration and expiration via pressure or flow changes in the ventilator circuit

48
Q

What is usually set in case of apnoea in BiPAP circuits?

A

A fixed back-up respiratory rate

49
Q

What are the main modes of invasive ventilation in children?

A
  • Intermittent mandatory ventilation (IMV)

- High frequency oscillatory ventilation (HFOV)

50
Q

What can IMV be divided into?

A

Pressure control (PC) and volume control (VC) ventilation

51
Q

What is set in PC ventilation?

A
  • Peak inspiratory pressure (PIP)
  • Positive end expiratory pressure (PEEP)
  • Inspiratory time (Tinsp)
  • Ventilator rate
  • Inspired oxygen
52
Q

What does expiration depend on when inspired breaths are delivered actively by the ventilator in PC ventilation?

A

The elastic recoil of the chest

53
Q

What determines the delivered tidal volume (TV) in PC ventilation?

A
  • PIP
  • Tinsp
  • Lung compliance
54
Q

What is meant by ‘synchronised mode’ in PC ventilation?

A

The ventilator delivers the PIP when the patient takes a breath

55
Q

What is synchronised mode in PC ventilation also known as?

A

Synchronised intermittent mandatory ventilation (SIMV-PC)

56
Q

When is SIMV-PC useful?

A

When ventilating non-paralysed patients and for weaning

57
Q

What happens in VC ventilation?

A

The patient is ventilated at a preset tidal volume (TV) and rate.
PEEP and inspired oxygen concentration is also set

58
Q

What is the result of the tidal volume being fixed in VC ventilation?

A

The pressure required to deliver the tidal volume varies depending on lung compliance

59
Q

What might result from non-compliant lungs with VC ventilation?

A

High peak airway pressure and associated barotrauma (ventilator associated lung injury, VALI)

60
Q

What is the result of VC ventilation being associated with a risk of VALI?

A

Volume modes of ventilation have traditionally not been favoured in paediatric intensive care

61
Q

Are spontaneous modes available in volume control ventilation?

A

Yes - called SIMV-VC

62
Q

What mode of non-invasive ventilation is PEEP analogous to?

A

CPAP

63
Q

How much PEEP is applied to mechanically ventilated patients in ICU?

A

Usually at least 4cm, even if the lungs are normal

64
Q

What is the purpose of PEEP in mechanically ventilated patients with normal lungs?

A

Prevent alveolar collapse during expiration and consequent atelectasis

65
Q

What levels of PEEP may be required in severe lung pathology?

A

Up to 15cm H2O

66
Q

What can very high levels of PEEP lead to?

A
  • Cardiovascular compromise
  • CO2 retention
  • Barotrauma
67
Q

How can very high levels of PEEP lead to cardiovascular compromise?

A

By impeding venous return to the heart

68
Q

When are synchronised modes of ventilation used?

A

During weaning

69
Q

Why are synchronised modes of ventilation used during weaning?

A

To allow the patient to begin to breathe spontaneously and take over the work of breathing

70
Q

What are synchronised modes also known as?

A

Support modes

71
Q

What kind of mechanical ventilation can be provided in support modes?

A

Pressure or volume support

72
Q

What happens in PS support modes?

A

Each spontaneous breath is augmented with a preset positive pressure

73
Q

What happens when pressure or volume support is combined with SIMV?

A

Support is provided when the patient takes a spontaneous breath above the set SIMV rate

74
Q

What is VALI?

A

A lung injury caused by high pressure (barotrauma) or high volume (volutrauma) ventilation

75
Q

How can VALI be limited?

A

Ensuring TV is 6-8ml/kg, and PIP is <35cm H2O

76
Q

What approach to carbon dioxide can allow ventilation to be minimised?

A

Permissive hypercapnia

77
Q

What happens in permissive hypercapnia?

A

An arterial pH of >7.25 is aimed for, rather than a specific CO2 target

78
Q

Why should oxygen be carefully titrated?

A

Because high levels of inspired oxygen be be toxic

79
Q

What SpO2 is aimed for in mechanical ventilation?

A

No higher than 92%, unless there are special circumstances

80
Q

What does judicious use of PEEP optimise?

A

Alveolar recruitment, which results in a lower FiO2

81
Q

What does high frequency oscillatory ventilation (HFOV) deliver?

A

Low tidal volumes, typically around 2ml/kg, at a rate of >150 breaths per minute

82
Q

How is the tidal volume delivered in HFOV?

A

By a pressure sine wave oscillating around a mean airway pressure

83
Q

What does the tidal volume act as in HFOV?

A

A constant distending pressure

84
Q

What is the effect of the constant distending pressure in HFOV?

A

It improves alveolar recruitment and ventilation/perfusion matching

85
Q

What are the mechanisms of gas exchange in HFOV?

A

Not clear, but probably include convection and molecular diffusion

86
Q

What is the role of HFOV?

A

Form of rescue ventilation, which is often used when conventional ventilation fails

87
Q

At what values of MAP/FiO2 might FOV be beneficial?

A

When mean airway pressure is >16, and FiO2 Is >0.6

88
Q

Does HFOV reduce barotrauma?

A

There are theoretical reasons it might, but not been proven compared to conventional ventilation

89
Q

What is respiratory failure caused by?

A

Failure to ventilate or failure to oxygenate

90
Q

What characterises respiratory failure caused by failure to ventilate?

A

Increased arterial CO2

91
Q

What characterises respiratory failure caused by failure to oxygenate?

A

Decreased arterial oxygen tension

92
Q

What might failure to oxygenate result from?

A
  • Decreased alveolar oxygen tension
  • Reduced oxygen diffusion capacity
  • Ventilation perfusion mismatch
93
Q

What is the treatment for respiratory failure caused by failure to ventilate?

A

Increase patients alveolar ventilation

94
Q

What is the treatment for respiratory failure caused by failure to oxygenate?

A

Restoration and maintenance of lung volumes, using recruitment manoeuvres and increased airway pressures

95
Q

What does arterial oxygenation depend on in conventional forms of ventilation?

A

FiO2 and airway pressure (PIP and PEEP)

96
Q

What does arterial oxygenation depend on in HFOV?

A

FiO2 and mean airway pressure

97
Q

What is carbon dioxide clearance dependent on in traditional ventilation?

A

Alveolar ventilation

98
Q

What is alveolar ventilation dependent on?

A

Minute volume

99
Q

How is minute volume calculated?

A

Tidal volume x respiratory rate

100
Q

What is carbon dioxide clearance dependent on in HFOV?

A

Minute volume

101
Q

What can increase minute volume in HFOV?

A

Increase the amplitude of the sine wave, and reducing the set frequency of the oscillatory waveform

102
Q

What is inhaled NO?

A

A potent pulmonary vasodilator

103
Q

What affect does inhaled NO have in the lungs?

A

It causes pulmonary arteriolar smooth muscle dilatation via a cGMP-dependent mechanism

104
Q

Where has inhaled NO been proven to have benefit?

A

In the neonatal period in meconium aspiration syndrome

105
Q

Who might benefit from inhaled NO (but no clinical trials to prove benefit)?

A
  • Older children with severe refractory hypoxaemic respiratory failure
  • May protect patients whose oxygenation might otherwise depend on potentially damaging ventilatory strategy
106
Q

What is ECMO?

A

A modified form of cardiopulmonary bypass which can be used to provide respiratory or cardiovascular support

107
Q

What happens in ECMO?

A

Deoxygenated blood is drained from the venous system, is heparinised and oxygenated outside the body via a membrane oxygenator, and pumped back into the body via a roller or centrifugal pump

108
Q

Where is the blood returned to the body in ECMO?

A

Into the arteries in veno-arterial ECMO, or into the veins in veno-venous ECMO

109
Q

What is the difference between veno-arterial (VA) and veno-venous (VV) echo?

A

VV provides respiratory support, VA provides cardiovascular and respiratory support

110
Q

What are the main indications for ECMO?

A
  • Severe hypoxaemic respiratory failure
  • Cardiogenic shock
  • Cardiac arrest
  • Failure to wean from cardiopulmonary bypass after cardiac surgery
  • As a bridge to either cardiac transplantation or placement of ventricular assist device
111
Q

What are the relative contraindications to ECMO?

A
  • Significant co-morbidities
  • Age and size of patient and in neonates
  • Presence of intraventricular haemorrhage
112
Q

Why shouldn’t ECMO be used in children with respiratory failure ventilated <7 days?

A

To avoid offering ECMO to children with irreversible lung injury who are unlikely to recover

TAS Emergencies and Critical Care ✅ (8 decks)

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