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(Edited) Respiratory System > S7) Respiratory Failure > Flashcards

S7) Respiratory Failure Flashcards

1
Q

What is respiratory failure?

A

Respiratory failure is a condition which results from inadequate gas exchange by the respiratory system so that arterial oxygen, carbon dioxide or both cannot be kept at normal levels

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2
Q

What is Type 1 Respiratory Failure?

A

- Type 1 Respiratory Failure is defined as a low pO2 (< 8 kPa) or O2 saturation (<90%) in breathing room air at sea level

  • pCO2 might be normal or low
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3
Q

What is Type 2 Respiratory Failure?

A

Type 2 Respiratory Failure is defined as a low pO2 (< 8 kPa) and high pCO2

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4
Q

Identify 5 conditions which might cause hypoxia

A
  • Low inspired pO2
  • Hypoventilation
  • Ventilation/perfusion mismatch
  • Diffusion defect in the alveolar capillary membrane
  • Right to left shunt eg. cyanotic heart disease
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5
Q

What is hypoventilation?

A

Hypoventilation is when the entire lung is poorly ventilated and alveolar ventilation (minute volume) is reduced

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6
Q

State 2 effects of hypoventilation

A
  • Hypoxaemia as alveolar pO2 falls → arterial pO2 falls
  • Hypercapnia as alveolar pCO2 rises → arterial pCO2 increases
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7
Q

Acute hypoventilation requires urgent treatment and possible artificial ventilation.

Identify 3 conditions where this can occur

A
  • Opiate overdose
  • Head injury
  • Very severe acute asthma
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8
Q

Describe 3 features of chronic hypoventilation

A
  • Chronic hypoxia and chronic hypercapnia
  • Slow onset and progression
  • Time for compensation so better tolerated
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9
Q

Identify a condition where chronic hypoventilation is observed

A

Severe COPD – most common cause of chronic type 2 respiratory failure

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10
Q

Identify a condition involving the respiratory centre in the brainstem that results in hypoventilation

A

Head injury

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11
Q

Identify a condition involving the spinal cord that results in hypoventilation

A

Trauma to the cervical spinal cord (phrenic and intercostal nerves)

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12
Q

Identify a condition involving the phrenic and intercostal nerves that results in hypoventilation

A

Guillain-Barré syndrome

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13
Q

What is Guillain-Barré syndrome?

A

Guillain–Barré syndrome is a rare and serious condition causing rapid-onset muscle weakness due to the immune system damaging the peripheral nervous system

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14
Q

Identify a condition involving the neuromuscular junction that results in hypoventilation

A

Myasthenia gravis

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15
Q

Identify 2 conditions involving the muscles of respiration that result in hypoventilation

A
  • Myopathy
  • Motor neurone disease
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16
Q

Identify 2 conditions involving the chest wall that result in hypoventilation

A
  • Severe obesity
  • Kyphoscoliosis
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17
Q

What is kyphoscoliosis?

A

Kyphoscoliosis is a deformity of the spine characterised by abnormal curvature of the vertebral column in the lateral and anterior planes

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18
Q

Identify 2 conditions involving the pleural cavity that result in hypoventilation

A
  • Pneumothorax
  • Pleural effusion (large)
19
Q

Identify 2 conditions involving poor lung compliance that result in hypoventilation

A
  • Respiratory distress of the newborn
  • Lung fibrosis
20
Q

Identify 2 conditions involving high airway resistance that result in hypoventilation

A
  • Very severe acute asthma
  • COPD (late stages)
21
Q

Identify a condition involving upper respiratory failure that results in hypoventilation

A

Laryngeal oedema

22
Q

Identify 5 conditions where chronic Type II Respiratory Failure is observed

A
  • Myopathy
  • Severe obesity
  • Lung fibrosis
  • Kyphoscoliosis
  • COPD
23
Q

State 4 effects of hypoxaemia

A
  • Impaired CNS function (confusion & irritability)
  • Cyanosis
  • Cardiac arrhythmias
  • Hypoxic vasoconstriction of pulmonary vessels
24
Q

What is cyanosis?

A

Cyanosis is the bluish discolouration of the skin and mucous membranes due to presence of >50gm/litre of unsaturated Hb

25
Q

Where is central cyanosis seen and what does it indicate?

A
  • Seen in oral mucosa, tongue and lips
  • Indicates hypoxaemia
26
Q

Where is peripheral cyanosis seen and what does it indicate?

A
  • Seen in fingers, toes
  • Indicates poor local circulation
27
Q

State the relationship between central and peripheral cyanosis

A

If central cyanosis is present, peripheral cyanosis will also be present

28
Q

State the compensatory mechanisms seen in chronic hypoxaemia to increase oxygen delivery

A
  • Increased EPO secreted by kidney → raised Hb (polycythaemia)
  • Increased 2,3, BPG
29
Q

State 3 results of the chronic hypoxic vasoconstriction of pulmonary vessels seen in chronic hypoxaemia

A
  • Pulmonary hypertension
  • Cor pulmonale (right heart failure)
30
Q

State 4 effects of hypercapnia

A
  • Respiratory acidosis
  • Impaired CNS function (drowsiness, confusion, coma, tremors)
  • Peripheral vasodilatation (warm hands, bounding pulse)
  • Cerebral vasodilation (headache)
31
Q

What is the compensatory mechanism seen in chronic hypercapnia?

A

Respiratory acidosis compensated by retention of HCO3- by kidney

32
Q

In 5 steps, outline the impact of chronic CO2 retention on the central chemoreceptors

A

⇒ CO2 diffuses into CSF and pH drops

⇒ Central chemoreceptors are stimulated

⇒ Choroid plexus cells secrete HCO3- into CSF to correct low pH

⇒ CSF pH normalises despite high blood pCO2

⇒ Central chemoreceptors now unresponsive to this pCO2

33
Q

Explain why the treatment of hypoxia may worsen hypercapnia

A
  • O2 removes stimulus for the hypoxic respiratory drive and alveolar ventilation falls, worsening hypercapnia
  • Removes pulmonary hypoxic vasoconstriction, increasing perfusion of poorly ventilated alveoli & diverting blood away from better ventilated alveoli
34
Q

How can one treat hypercapnia?

A
  • Controlled oxygen therapy with a target saturation of 88-92%
  • Ventilatory support if oxygen therapy causes rise in pCO2
35
Q

V/Q matching happens at alveolar level.

When does optimal gas exchange occur?

A

V/Q ratio = 1

36
Q

What happens when V/Q ratio < 1? (hypoventilation)

A
  • Alveolar pO2 falls
  • Alveolar pCO2 rises
37
Q

What happens when V/Q ratio > 1? (hyperventilation)

A
  • Alveolar pO2 rises
  • Alveolar pCO2 falls
38
Q

V/Q mismatches occur in disorders where some alveoli are being poorly ventilated.

Identify and describe 5 conditions

A
  • Asthma (variable airway narrowing)
  • Pneumonia (exudate in affected alveoli)
  • RDS in newborn (some alveoli not expanded)
  • Pulmonary oedema (fluid in alveoli)
  • Pulmonary embolism
39
Q

In 4 steps, explain how the body responds to a V/Q ratio < 1

A

⇒ Hypoxic vasoconstriction occurs to diverts some blood to better ventilated areas

⇒ Mixed blood in left atrium (low arterial pO2 and high arterial pCO2)

⇒ Central and peripheral chemoreceptors are stimulated

⇒ Hyperventilation occurs

40
Q

In 4 steps, explain how a pulmonary embolism can lead to hypoxaemia

A

⇒ Embolus redistributes of pulmonary blood flow

⇒ Blood is diverted to unaffected areas of pulmonary circulation

⇒ V/Q ratio < 1 if hyperventilation cannot match the increased perfusion

⇒ Hypoxaemia

41
Q

Fibrotic lung disease is when the thickened alveolar membrane slows gas exchange.

Identify 4 conditions causing lung fibrosis

A
  • Idiopathic Fibrosing alveolitis
  • Asbestosis
  • Extrinsic allergic alveolitis
  • Pneumoconiosis
42
Q

How do diffusion defects cause Type I respiratory failure?

A
  • Poor diffusion across alveolar capillary membrane
  • Leads to low O2 and normal/low pCO2
43
Q

Why is a low pO2 observed in diffusion defects but pCO2 is normal(/low)?

A

CO2 is more soluble so its diffusion less affected than O2 diffusion

(Edited) Respiratory System (19 decks)

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