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Respiratory failure Flashcards

1
Q

What is respiratory failure?

A

Impairment of gas exchange causing hypoxaemia with or without hypercapnia - can be acute or chronic

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2
Q

Type 1 respiratory failure

A

Hypoxaemia (low paO2)
Low or normal CO2

Gas exchange impaired at alveolar capillary membrane

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3
Q

Type 2 respiratory failure

A

Hypoxaemia (low paO2)
Hypercapnia (high CO2)

Reduced ventilatory effort or inability to overcome increased resistance to ventilation (pump failure)

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4
Q

What is the cut off for hypoxaemia for respiratory failure?

A

paO2 less than 8 kPa
or O2 saturations less than 90%

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5
Q

What can happen with prolonged type 1 respiratory failure?

A

Can progress to type 2

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6
Q

Hypoxaemia vs hypoxia

A

Hypoxaemia - low pO2 in arterial blood (all about partial pressure)

Hypoxia - O2 deficiency at tissue level, demands not met

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7
Q

Normal O2 sats and paO2

A

anything above 94% is normal (only resp failure at 90%)

10.6-13.3kPa normal (not resp failure until less than 8)

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8
Q

What level of O2 sats and pO2 is tissue damage likely to occur?

A

O2 sats less than 90%
pO2 less than 8kPa

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9
Q

What level of O2 sats and pO2 is tissue damage likely to occur?

A

O2 sats less than 90%
pO2 less than 8kPa

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10
Q

Can tissues be hypoxic without hypoxaemia?

A

Yes - eg in anaemia paO2 can be normal (no hypoxaemia) but tissues can be hypoxic due to lack of Hb

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11
Q

What sats are likely if pt is presenting with central cyanosis?

A

Sats must be below 85% to get central cyanosis

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12
Q

How to check central cyanosis?

A

Check lips, tongue, oral mucosa

Darker skin - may be easier to see cyanosis in mucous membranes

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13
Q

What will be present alongside central cyanosis?

A

Peripheral cyanosis

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14
Q

Signs of hypoxaemia

A

Impaired CNS - confusion, irritability, agitation, drowsy

Cardiac arrhythmias

Hypoxic vasoconstriction of pulmonary vessels

Central cyanosis

Tachypnoea

Tachycardia

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15
Q

What occurs in chronic hypoxaemia?

A

Compensatory mechanisms increase O2 delivery and decrease hypoxia (tissues get O2)

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16
Q

Compensatory mechanisms induced in chronic hypoxaemia

A

Increased erythropoietin from kidney = raised Hb

Increased 2,3 DPG - shifts Hb/O2 curve to right (Hb has lower affinity for O2)

Increased capillary density

Hypoxic vasoconstriction of pulmonary vessels

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17
Q

What does chronic hypoxic vasoconstriction of pulmonary vessels cause?

A

Pulmonary hypertension
Right heart failure
Cor pulmonale - enlargement of R side of heart

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18
Q

6 causes of hypoxaemia

A

Low inspired pO2 eg high altitude

Ventilation perfusion (V/Q) mismatch

Diffusion defect - alveolar membrane

Intra-lung shunt eg ARDS

Hypoventilation

Extra-pulmonary shunt eg congenital heart defects

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19
Q

Low inspired O2 as a cause for hypoxaemia explained

A

Partial pressure of O2 decreases as you get further from sea level (higher altitudes)

pAO2 falls (alveolar pO2)

= low paO2 (arterial O2)

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20
Q

pO2 equation that helps explain low inspired O2 resulting in hypoxaemia

A

pO2 = FiO2 (fraction inspired O2) x total atmospheric pressure

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21
Q

Treatment for low inspired O2 cause of hypoxaemia

A

O2 !!! - will fully improve as there is no other problem

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22
Q

Scenarios when V/Q mismatch can occur

A

Asthma (airway narrowing)

COPD (airway narrow/collapse alveoli)

Pneumonia (exudate affecting alveoli)

RDS (alveoli not expanded from high surface tension from lack of sufficient surfactant)

Pulmonary oedema (fluid in alveoli)

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23
Q

Treatment for V/Q mismatch causing hypoxaemia

A

O2 but need to correct underlying pathology

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24
Q

What does it mean if V/Q is less than 1

A

V has decreased, perfusion has not changed

Blood equilibrates to new alveolar pO2 - decreases
pCO2 increases due to poor removal of CO2

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25
Q

What happens when low paO2 and high pCO2 is sensed?

A

Hyperventilation is induced by chemoreceptors (sense hypercapnia in central and hypoxaemia in peripheral)

If severe lung disease, hyperventilation may not be able to compensate

26
Q

What occurs to alveolus in pulmonary embolism?

A

The lack of perfusion makes air in that alveolus pointless - increased dead space as cannot diffuse

27
Q

V/Q ratio in pulmonary embolism

A

In affected alveolus that is not getting supplied - V/Q is greater than 1 (perfusion is problem)

In alveolus that is now getting more blood due to diversion V/Q is less than 1 as ventilation cannot match increased perfusion (if hyperventilation cannot match)

28
Q

What do diffusion defects lead to in ABG’s?

A

pO2 is low
pCO2 is usually normal or low

29
Q

Why is CO2 normal or low in diffusion defect but O2 is affected?

A

CO2 is much more soluble than O2 so is affected much later by diffusion problems#

(Type 1 initially and then type 2)

30
Q

Causes of diffusion impairement

A

Fibrotic lung disease - thickened alveolar membrane

Pulmonary oedema - fluid in interstitial space increases diffusion distance

31
Q

Causes of lung fibrosis affecting diffusion

A

Idiopathic pulmonary fibrosis

Asbestos

Extrinsic allergy alveolitis

Pneumoconiosis (inhaling particles that damage lung)

32
Q

Treatment of diffusion impairment of lung

A

Oxygen administration will improve

33
Q

What is intra-pulmonary shunt?

A

When blood passes the alveolus and does not get oxygenated - leaves in the same state as it was when it arrived

34
Q

Causes of intra-pulmonary shunt

A

Alveoli damage eg in acute respiratory distress syndrome

35
Q

Explain ARDS as a cause for intra-pulmonary shunt

A

Widespread acute alveolar injury
All mechanisms cause damage to alveolar capillary unit

36
Q

Lungs in ARDS

A

Heavy
Red
Showing congestion and oedema - alveoli contain fluid and lined by hyaline membranes

37
Q

Vascular effects of ARDS

A

Increased vascular permeability, oedema, fibrin exudate

38
Q

What causes ARDs?

A

Loss of surfactant = alveolar atelectasis
Lungs become stiff and less compliant
Volume of lung decreases

39
Q

Treatment for when ARDs causes intrapulmonary shunt

A

Hard to manage on ventilator - 100% O2 sometimes does not correct hypoxaemia

May need positive pressure ventilation to open alveoli

40
Q

What respiratory failure does hypoventilation cause?

A

Type 2

41
Q

What does it mean when hypoventilation causes hypoxaemia

A

Entire lung poorly ventilated due to inadequate resp rate or inadequate volume of alveolar ventilation

42
Q

Mechanism of hypoventilation causing hypoxaemia and the type 2 respiratory failure

A

Alveolar ventilation (minute volume) reduced –>
Alveolar pO2 reduces
Arterial pO2 falls = hypoxaemia

Alveolar pCO2 rises –> arterial CO2 rises = hypercapnia

43
Q

What respiratory failure does hypoventilation cause?

A

Type 2 - hypoventilation ALWAYS causes hypercapnia

44
Q

Treatment of hypoventilation

A

Hypoxaemia will improve with O2 added
BUT hypercapnia not solved by this as ventilation is problem

45
Q

Acute hypoventilation vs chronic how is urgency different

A

Acute - needs urgent treatment +/- artificial ventilation

Chronic - slow onset and progression, time for compensation, better tolerated

46
Q

Common causes of acute hypoventilation

A

Opiate overdose
Head injury
Severe acute asthma

47
Q

Common causes of chronic hypoventilation

A

Severe COPD
(acute exacerbations can occur in LRT infection)

48
Q

How can asthma cause hypoventilation?

A

Mucous plugging can occur - hypoventilation as the lungs can’t expand

Severe constriction with attack

49
Q

Central disorders which can cause type 2 respiratory failure (via hypoventilation)

A

Central sleep apnoea
Obesity hypoventilation syndrome
Narcotic overdose
Sedatives
Medullary disorders
Hypothyroidism
CNS trauma/Brainstem herniation

50
Q

Disorders of the neuromuscular junction

A

Myasthenia gravus
Organophosphate toxicity
Botulism

51
Q

Diseases/conditions causing respiratory muscle weakness/fatigue causing respiratory failure

A

COPD
Asthma
Malnutrition
Diaphragmatic dysfunction
Muscular dystrophy
RDS
Severe restrictive lung disease

52
Q

Chest wall disorders which can cause respiratory failure

A

Scoliosis - sideways curvature

Kyphosis - outwards curvature (hunch back)

Kyphoscoliosis - both

53
Q

How do chest wall disorders cause resp failure?

A

Disordered movement of chest wall
Chest wall compliance reduced and unable to expand as well
Lung compliance is reduced due to small parts of lung partially collapsing or partially inflating

54
Q

Acute effects of hypercapnia

A

Respiratory acidosis

Impaired CNS - drowsy, confused, coma, tremors

Peripheral vasodilation - warm hands, bounding pulse

Cerebral vasodilation - headache

55
Q

Chronis hypercapnia effects

A

Respiratory acidosis compensated by retention of HCO3 by kidney

CNS effects acclimatised to - CSF pH is normalised by choriod plexus and central chemoreceptors set to new normal

Vasodilation mild but may still be present - pink

56
Q

Why does treatment of type 2 respiratory failure with O2 worsen hypercapnia?

A

Correction of hypoxia removes pulmonary arteriole hypoxic vasoconstriction
(poorly ventilated alveoli are now perfused, blood is diverted away from better ventilated alveoli because body is like WOW some oxygen)

Haldene effect - oxygenated haemoglobin has low affinity for CO2 in oxygenated state to CO2 disassociates into blood

57
Q

How to give O2 in type 2 resp failure

A

Give controlled therapy with target sats of 88-92%

If oxygen causes rise in pCO2 - need ventilation (assisted or mechanical)

58
Q

How does type 1 progress to type 2 resp failure?

A

As more areas of the lung become involved and fatigued

  • asthma exacerbation, end stage COPD
59
Q

Is there only 1 cause for someones resp failure?

A

NO can have multiple mechanisms causing failure

60
Q

What is hypoventilation always related to?

A

Hypercapnia!!!

Respiratory (21 decks)

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