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Resp > Lecture 14 - Hypoxaemia and resp failure > Flashcards

Lecture 14 - Hypoxaemia and resp failure Flashcards

1
Q

Hypoxaemia

A

Low pO2 in blood

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2
Q

Hypoxia

A

Low O2 at body tissue level

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3
Q

Hypoxic without hypoxaemia

A

Severe anaemia - reduced carrying capacity of Hb but same dissolved pO2

Poor circulation - MI

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4
Q

O2 saturation and pO2

A

94% - 98%

9.3 - 13.3 kPa

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5
Q

Tissue damage

A

When pO2 less that 8kPa

Less than 90% perfusion

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6
Q

Maintenence of pO2

A 
Normal inspired pO2
Normal alveolar ventilation 
Ventilation/ perfusion
Normal alveolar capillary membrane
Normal circulation
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7
Q

Causes if hypoxaemia

A
  1. Low inspired O2 - high altitude
  2. Hypoventilation
  3. V/Q mismatch
  4. Diffusion defect - problems with alveolar capillary membrane
  5. Acute respiratory distress syndrome
  6. Right to left shunt - cyanosis
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8
Q

Adaptations of people living at high altitudes

A

Polycythaemia - increased Hb
2,3 - bisphosphoglycerate
Increased capillary density in tissues

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9
Q

Effects of hypoxaemia

A 
Confusion
Irritability 
Agitation
Cardiac arrythmias and cardiac ischaemia
Central cyanosis - 50% O2 saturation
Vasoconstriction of pulmonary arteries
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10
Q

Compensatory mechanisms to increase O2 delivery

A
  • Increased EPO production by kidney - raised Hb (polycythaemia)
  • Increased 2,3- BPG
  • Chronic hypoxic vasoconstriction of pulmonary blood vessels
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11
Q

Chronic hypoxic vasoconstriction of pulmonary blood vessels

A

Pulmonary hypertension
Cor pulmonale
RSH hypertrophy and arrythmias

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12
Q

Type 1 respiratory heart failure

A

Low O2

Normal or low CO2

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13
Q

Type 2 respiratory heart failure

A

Low O2

High CO2

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14
Q

Hypoventilation

A

Always type 2 respiratory failure

Hypoxia and hypercapnia

Corrected with O2

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15
Q

Causes of acute hypoventilation

A

Opiate overdose
Head injury
Very severe acute asthma

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16
Q

Causes of chronic hypoventilation

A 
Severe COPD
Acute exacerbations of lower respiratory tract infections
Lung fibrosis 
Severe obesity  
Scoliosis and kyphoscoliosis
17
Q

Scoliosis

A

Sideways curvature of the spine

18
Q

Kyphoscoliosis

A

Excessive outward curve of the spine and sideways curvature of spine

19
Q

Hypercapnia

A 
Causes by hypoventilation
Respiratory acidosis 
- confusion
- drowsiness
- coma

Peripheral vasodilation - warm hands and bounding pulse

Cerebral vasodilation - headache `

20
Q

Chronic hypercapnia consequences

A

Resp acidosis compensated by HCO3-

CNS creates a new CO2 set point

Vasodilation more mild - red face

21
Q

O2 ventilation in Type 2 dangers

A

Treatment of O2 improves pO2 however removes the hypoxic resp drive for by peripheral chemoreceptors

Therefore can hypoventilate making pCO2 worse

Also removes hypoxic vasodilation of pulmonary artery branches so blood is diverted away from better ventilated alveoli

22
Q

Oxygen therapy

A

Target saturation 88% - 92%

If causes rise in pCO2 - ventilatory support

23
Q

Type 1 resp failure V/Q mismatch

A
  1. Ventilation decreases due to e.g. asthma
  2. pO2 drops and pCO2 increases initially
  3. Compensatory hyperventilation and shunting of blood to better diffused alveoli
  4. pO2 rises a small amount in well perfused alveoli as already saturated
  5. pCO2 decrease has a greater effect and corrects hypercapnia in normally perfused segments.
  6. Type 1 resp failure as low O2 and normal or low CO2 `
24
Q

Causes of V/Q mismatch

A 
Asthma
Pneumonia
RDS
Pulmonary embolism
Pulmonary oedema
25
Q

Pulmonary embolism resp failure

A

Will cause type 1 resp failure

26
Q

Poor diffusion across alveolar membrane

A

Affects O2 more and CO2 more soluble

Type 1 resp failure

27
Q

Causes of poor diffusion across alveolar membrane

A

Fibrotic lung disease - thickened alveolar membrane

Pulmonary oedema - fluid in interstitial space increases diffusion pathway

28
Q

Causes of lung fibrosis

A

Asbestos
Idiopathic
Extrinsic allergic alveolitis

29
Q

Acute respiratory distress syndrome ventilation

A

Ventilation = 0
Still perfused

V/Q < 1 (=0)

Type 1 resp failure develops into type 2

Resp (22 decks)

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