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Respiratory System > Respiratory Failure > Flashcards

Respiratory Failure Flashcards

1
Q

What is hypoxaemia?

A

Low pO2 in arterial blood
<10.6kPa

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2
Q

What is hypoxia?

A

O2 deficiency at tissue level

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3
Q

What is normal O2 saturation?

A

94-98%

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4
Q

What is the normal range for PaO2?

A

10.6-13.3kPa

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5
Q

At what O2 saturation is tissue damage most likely?

A

<90%

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6
Q

At what pO2 is tissue damage most likely?

A

<8kPa

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7
Q

What is respiratory failure?

A

Impairment in gas exchange causing hypoxaemia +/- hypercapnia
Type 1 without
Type 2 with

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8
Q

What is type 1 respiratory failure?

A
  • impairment of gas exchange causing hypoxaemia WITHOUT hypercapnia
  • low PaO2 <8kPa or O2 sats <90%
  • pCO2 normal or low
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9
Q

What is type 2 respiratory failure?

A
  • impairment of gas exchange causing hypoxaemia WITH hypercapnia
  • low PaO2 <8kPa AND high PaCO2 >6.5kPa
  • respiratory pump failure
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10
Q

Signs of hypoxaemia

A
  • impaired CNS function > confusion + irritability
  • central cyanosis
  • Tachypnoea
  • tachycardia
  • cardiac arrhythmias + cardiac ischaemia
  • hypoxic vasoconstriction of pulmonary vessels (can cause pulmonary hypertension)
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11
Q

What are the oxygen stats of a patient with central cyanosis?

A

<85%

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12
Q

What are compensatory mechanisms to increase oxygen delivery (+ decrease hypoxia)?

A
  • increased EPO secreted by kidney > raised Hb
  • increased 2,3 DPG > shifts Hb/O2 dissociation curve to right > O2 released more freely
  • increased capillary density
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13
Q

What can chronic hypoxic vasoconstriction of pulmonary vessels result in?

A
  • Pulmonary hypertension
  • Right heart failure
  • Cor pulmonale: hypertrophy of right side of heart
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14
Q

Causes of hypoxaemia

A
  • low inspired FiO2 e.g. high altitude
  • V/Q mismatch
  • diffusion defect (problems of alveolar capillary membrane)
  • intra-lung shunt - acute respiratory distress syndrome
  • hypoventilation
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15
Q

What is the most common cause of hypoxaemia?

A

V/Q mismatch

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16
Q

List some causes of V/Q mismatch

A
  • asthma
  • COPD
  • pnemonia
  • respiratory distress syndrome in newborn
  • pulmonary oedema
  • pulmonary embolism
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17
Q

Treatment of V/Q mismatch

A
  • improves with O2 administration
  • underlying pathology must be corrected for O2 to completely correct hypoxaemia
18
Q

What happens to PaO2 and PaCO2 in V/Q mismatch due to inadequate ventilation?

A
  • PaO2 falls
  • PaCO2 rises

Blood equilibrates to new alveolar PaO2 + PaCO2

19
Q

What is the V/Q ratio in a pulmonary embolism?

A

> 1
Due to poor perfusion

20
Q

What does poor diffusion across the alveolar membrane cause in terms of respiratory failure?

A
  • initally type 1 respiratory failure pCO2 normal or low + pO2 low
  • as disease progresses, restrictive lung disease leads to hypoventilation > hypercapnia: pCO2 high (type 2 respiratory failure)
21
Q

Causes of diffuse lung fibrosis

A
  • idiopathic
  • asbestosis: exposure to asbestos
  • extrinsic allergic alveolitis
  • pneumoconiosis: inhalation of dust particles
22
Q

Reasons for intrapulmonary shunts

A
  • collapsed alveolus
  • fluid filled alveolus

no gas exchange in that area

23
Q

Example of intrapulmonary shunt

A

Acute respiratory distress syndrome

24
Q

What occurs in acute respiratory distress syndrome?

A
  • loss of surfactant > causes alveolar atelectasis
  • exudate in lungs
  • lung becomes stiff (less compliant) > lung volume decreases
  • loss of hypoxic pulmonary vasoconstriction mechanism
  • intrapulmonary shunt due to no ventilation with respect to perfusion
25
Q

Treatment to acute respiratory distress syndrome

A
  • hard to manage on ventilator
  • even 100% O2 may not correct hypoxaemia
  • need to add positive pressure ventilation to open the alveoli
26
Q

What is hypoventilation?

A

The entire lung is poorly ventilated due to inadequate respiratory rate or volume of alveolar ventilation

27
Q

What does hypoventilation cause in terms of respiratory failure?

A
  • ventilation reduced
  • alveolar pO2 falls > arterial pO2 falls > hypoxaemia
  • alveolar pCO2 rises > artieral pCO2 rises > hypercapnia
  • Type 2 respiratory failure
28
Q

Causes of acute hypoventilation

A
  • opiate overdose
  • head injury
  • very severe acute asthma
29
Q

Causes of chronic hypoventilation

A

Severe COPD

30
Q

Is acute or chronic hypoventilation tolerated better?
Why?

A

Chronic
Slow onset + progression so there is time for compensation

31
Q

Effects of acute hypercapnia

A
  • respiratory acidosis
  • impaired CN function > drowsy, confusion, flapping tremor, coma
  • peripheral vasodilation >warm hands + bounding pulse
  • cerebral vasodilation > headache
32
Q

Why can treatment of hypoaxemia worsen hypercapnia?

A
  1. Correction of hypoxia removes pulmonary arteriole hypoxic vasoconstriction
    - this leads to increased perfusion of poorly ventilated alveoli
    - blood diverted away from better ventilated alveoli
    - V/Q mismatch worsens
  2. Haldane mechanism
    - oxygenated haemoglobin has low affiliated for CO2 > CO2 dissociates from Hb into blood
33
Q

How does pneumonia cause V/Q mismatch?

A

Exudate in affected alveoli
Reduced ventilation

34
Q

What is atelectasis?

A

Partial collapse or incomplete inflation of lung

35
Q

Effects of chronic hypercapnia

A
  • respiratory acidosis compensated by retention of HCO3- by kidney
  • vasodilation mild but still present
36
Q

What is scoliosis?

A

Sideways curvature of the spine

37
Q

What is kyphosis?

A

Excessive outward curve of spine
Abnormal rounding of upper back

38
Q

What is kyphoscolosis?

A

Both scoliosis + kyphosis
Sideways curvature + excessive outward curve of spine

39
Q

What conditions can cause hypoventilation?

A
  • gullien barre syndrome
  • kypohoscoliosis
  • myasthenia gravis
  • COPD + asthma due to muscle weakness/fatigue
  • motor neurone disease
40
Q

What is the mechanism explains why a patient with kyphoscoliosis can develop respiratory failure?

A
  • Hypoventilation
  • Due to inability to adequately expand the thoracic cavity during inspiration
  • Cannot adequately decrease intrapulmonary pressure relative to atm
  • inspiration is compromised

Respiratory System (25 decks)

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