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Resp > Lecture 7 - Resp Failure > Flashcards

Lecture 7 - Resp Failure Flashcards

1
Q

What is Type 1 Respiratory failure?

A

Impairment of gas exchange where’s theres Hypoxaemia with or without hypercapnia

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2
Q

What are the key values of PaO2 and pCO2 for Type 1 respiratory failure?

A

Low paO2 < 8kPa or O2 sat <90%

PCO2 normal or low

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3
Q

Why can pCO2 be normal or low in Type1 respiratory failure?

A

Due to the hypoxaemia the patient may be hyperventilating which would cause the low levels of CO2 (hypocapnia)

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4
Q

What is Type 2 respiratory failure?

A

Where patient is both hypoxaemic and hypercapnic

So its basically a reduced ventilatory effort/pump failure

Not removing enough CO2 and not getting enough O2

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5
Q

What is Hypoxaemia?

A

Low pO2 in arterial blood

Hypoxaemia can go on to cause hypoxia

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6
Q

What is Hypoxia?

A

When theres O2 deficiency at the tissues

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7
Q

In what situation can tissues be hypoxia without hypoxaemia?

A

Anaemia
Poor circulation to tissues

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8
Q

What is the normal range for O2 sat?

A

94% - 98% on air

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9
Q

What O2 sat and pO2 is tissue damage likely at?

For pO2 what point is this on the oxygen disocciation curve?

A

O2 < 90%

PO2 < 8kPa. This is the steep part on the curve where a small change in pO2 causes a massive change in O2 sats

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10
Q

How does central cyanosis appear?

What oxygen saturation does it normally appear at?

A

Affects:
-oral mucosa
-tongue
-lips

Can appear below 90% or 85%

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11
Q

What are some signs/effects of hypoxaemia?

A

-Impaired CNS function (confusion, drowsy, irritability, agitation)
-cardiac ischaemia and cardica arrhythmias (cardiac tissue death leads to arrhythmias)
-hypoxic vasoconstriction of pulmonary vessels (COMPENSATORY MECHANISM)
-central cyanosis
-tachypnoea and tachycardia (COMPENSATORY MECHANISM)

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12
Q

What is a potential consequence of hypoxia vasoconstriction of pulmonary vessels if the Hypoxaemia is chronic?

A

Pulmonary hypertension

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13
Q

With chronic hypoxaemia, what are the 3 compensatory mechanisms employed by the body to increase O2 delivery reducing hypoxia?

A

Inc EPO production by kidney to inc Hb by making more Red cells (Polycythaemia)

Inc 2,3-Diphosphoglycerate production by red cells, shifts saturation curve to the right making the Hb give up O2 more readily to tissues

Inc capilary density

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14
Q

What are some consequences of chronic hypoxic vasoconstriction of pulmonary vessels?

A

Pulmonary hypertension
Right Heart failure
Cor pulmonale (abnormal enlargement of right side of heart due to disease of lungs or pulmonary vessels

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15
Q

What can cause Hypoxaemia?

A

Low inspired O2 in air (high altitude)

Ventilation:Perfusion mismatch

Diffusion defect (problems of alveolar capillary membrane)

Intra-lung shunts (where blood skips out on gas exchange, can happen in Acute/Adult Respiratory Distress Syndrome

Hypoventillation

Extrapulmoonary (Foramen ovale, ductus venosus

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16
Q

How does high altitude cause Hypoxaemia?

How can it be treated?

A

Low partial pressure of oxygen means the partial pressure of oxygen in arterial blood is low (hypoxaemia)

Just give oxygen

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17
Q

What can cause a V/Q mismatch due to poor ventilation?

A

Asthma (airway narrowing)
COPD (airway narrowing)
Pneumonia (exudate in affected alveoli)
RDS (some alveoli not expanded due to high surface tension cuz of lack of surfactant)
Pulmonary oedema (fluid in alveoli)

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18
Q

What happens to paO2 and paCO2 if someone has poor ventilation?

A

PaO2 falls
PaCO2 rises

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19
Q

What are the 2 main conditions causing a VQ lower than 1?

A

Indicates V is reduced

So asthma and COPD

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20
Q

What receptors detect Hypoxaemia causing hyperventilation?

A

Peripheral chemoreceptors

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21
Q

What receptors detect hypercapnia stimulating hyperventilation?

A

Central chemoreceptors

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22
Q

How does a pulmonary embolus affect V/Q?

A

Leads to the V/Q ratio increasing so its >1

All the alveoli are still getting ventilated but not perfused since the pulmonary embolus blocks some blood flow

But also causes V/Q to decrease in other areas since the body redirects blood from the affected areas leading to extra perfusion of the well ventilated areas (often hyperventilate to try and compensate)

23
Q

What is alveolar dead space?

A

Areas of alveoli that contain gas that dont take part in gas exchange

24
Q

In diffusion defects of the lungs, how are pO2 and pCO2 affected and why?

A

pO2 low
pCO2 normal or low

pO2 low since its way less soluble than CO2 so the increased diffusion difference massively affects its ability to enter body

pCO2 normal or low since it’s highly soluble so its levels aren’t really affected, can be low due to hyperventilation to try and compensate for the low pO2

25
Q

What type of respiratory failure do diffusion diseases initially cause?

A

Type 1 respiratory failure

26
Q

How can pulmonary fibrosis progress from Type 1 respiratory failure to Type 2 Respiratory failure?

A

The lungs become smaller and smaller since they struggle to expand (less compliant) the more fibrotic tissue that is deposited

This leads to hypoventilation which will cause the hypercapnia

27
Q

What are 2 diseases which can impair diffusion which can lead to respiratory failure?

A

Pulmonary fibrosis/fibrotic lung disease

Pulmonary oedema

28
Q

How does fibrotic lung disease cause respiratory failure?

A

The alveolar membrane is thickened by fibrotic tissue which slows/reduces ability to diffuse O2 into blood

29
Q

How does Pulmonary oedema impair diffusion leading to respiratory failure?

A

Fluid builds up in interstitial space which increases the diffusion distance
This reduces PO2

30
Q

What can cause diffuse lung fibrosis?

A

Idiopathic
Asbestosis
Pneumoconiosis
Extrinsic allergic alveolitis

Oxygen will improve

31
Q

What is atelectasis?

A

When the alveoli collapse

32
Q

What is an intrapulmonary shunt?

A

Where alveoli are perfused but are not ventilated

Cause V/Q to be 0

33
Q

What are some causes of Intrapulmonary shunts leading to hypoxaemia?

A

Things that cause no ventilation:
-alveoli filled with pus
-oedema fluid in alveoli
-blood in alveoli
-tumours of alveoli
-Acute Respiratory Distress Syndrome

34
Q

What is Acute Respiratory Distress Syndrome (ARDS)?
What coping mechanism does the body use?

A

When theres a loss of surfactant which leads to alveolar atelectasis
(MASSIVE INTRAPULMONARY SHUNTING)
Lungs become stiff and less compliant

Hypoxic pulmonary vasoconstriction occurs to direct blood away from collapsed alveoli

35
Q

How can you manage a patient with ARDS?

A

Ventilator
May need to add positive pressure ventilation to reopen alveoli

36
Q

What is hypoventialltion/how does hypoventillation cause Hypoxaemia?

A

When the entire lung is poorly ventilated due to bad respiratory rate or alveolar ventilation

37
Q

What type of respiratory failure is cause by hypoventilation?
Why?

A

Type 2 respiratory failure

pO2 is low (hyperoxaemia)
pCO2 is high (hypercapnia)

38
Q

What are some causes of Acute hypoventilation?

A

Opiate overdose (respiratory depression)
Head injury (respiratory centre in medulla affected)
Very severe acute asthma

39
Q

Why does acute hypoventillation need urgent treatment but chronic hypoventillation often doesn’t?

A

Chronic hypoventillation is slow in onset and progression so there is time for the body to compensate so its better tolerated

40
Q

What is the most common cause of chronic hypoventialltion?

A

Severe COPD (most common cause of chronic type 2 resp failure)

41
Q

What part of the brain is the respiratory centre located in?

A

Medulla oblongata

42
Q

What are some central disorders which cause hypoventilation?

A

Opioid Overdose
Sedatives
Medullary disorders
Central sleep apnoea
Obesity hypoventilation syndrome

43
Q

What motor disorders can cause hypoventialltion?

A

Tetanus (toxins from tetani bacteria)
ALS
Motor Neurone Disease
Spinal cord injury at C3 level (phrenic nerve)

44
Q

What are some disorders of neuromuscular junctions that cause hypoventillation?

A

Myasthenia Gravis

Organophosphate poisoning

Botulism

45
Q

What disease can lead to muscle weakness or fatigue causing hypoventilation?

A

COPD
Asthma
Malnutrition
Diaphragmatic dysfunction
Muscular dystrophy
Respiratory Distress Syndrome
Severe restrictive lung disease

46
Q

What are some chest wall disorders that can lead to hypoventilation?

A

Scoliosis
Kyphosis
Kyphoscooliosis

47
Q

What is scoliosis?

A

Sideways curvature of the spine

48
Q

What is kyphosis?

A

The excessive outward/forward curving of the spine resulting in abnormal rounding of the upper back preventing the proper expansion of the lungs

49
Q

What is kyphoscoliosis?

A

Both scoliosis and kyphosis (sideways curve and forward curve)

Reduces chest wall compliance and lung compliance

50
Q

What are the acute affects of hypercapnia?

A

Respiratory acidosis

CNS function impaired (drowsiness, confusion, coma, flapping tremors)

Peripheral vasodilation - warm hands, bounding pulse

Cerebral vasodilation (headache)

51
Q

What are the effects chronic hypercapnia?

A

Kidneys retain more HCO3- to compensate respiratory acidosis
Choroid plexus helps neutralise CSF by pumping in more HCO3-
Mild vasodilation

52
Q

Why can treatment of type 2 respiratory failure with oxygen (to treat the hypoxaemia) worsen hypercapnia?

A

Once the hypoxia is corrected, the pulmonary hypoxic vasoconstriction stops
This leads to blood flowing to poorly ventilated away from well ventilated alveoli again which worsens the V/Q mismatch so CO2 levels continue to build

Haldane mechanism (oxyhaemoglobin has low affinty for CO2 so it dissociated CO2 into blood

53
Q

How can Type 1 resp failure progress to type 2?

A

Disease progresses and more areas of lung are involved

Fatigue

Resp (23 decks)

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