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Respiratory (Revision) > 12 - Respiratory Failure > Flashcards

12 - Respiratory Failure Flashcards

1
Q

What are some examples of where tissues are hypoxic without hypoxaemia?

A
  • Anaemia
  • Poor circulation
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2
Q

At what oxygen saturation does tissue damage occur?

A
  • O2 <90%
  • pO2 < 8kPa
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3
Q

How can hypoxaemia occur?

A

For normal O2 need:

  • Normal inspire pO2
  • Normal alveolar ventilation
  • V/Q = 1
  • Normal alveolar capillary membrane
  • Cardiac output through lungs
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4
Q

What are some effects of hypoxaemia in the body?

A

- Impaired CNS function (confusion, agitation)

- Central cyanosis (mucous membranes >50gm/L of unsaturated Hb)

- Cardiac arrhythmias

- Hypoxic vasoconstriction

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5
Q

What is type 1 and type 2 respiratory failure?

A

Type 1: low pO2 (<8kPa) , normal or low pCO2

Type 2: low pO2 and high pCO2 (>6.7kPa)

Respiratory failure is when arterial pO2 falls below 8kPa when breathing air at sea level

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6
Q

What are some effects of hypercapnia on the body?

A
  • Respiratory acidosis
  • Impaired CNS function: drowsiness, confusion, coma, flapping tremors
  • Peripheral vasodilation: warm hands, bounding pulse
  • Cerebral vasodilation so headache
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7
Q

What are some compensatory mechanisms to chronic hypoxia and what are some issues with this compensatory mechanism?

A

- Increased EPO from kidney so increased Hb

- Increased 2,3 DPG to shift Hb saturation curve

- Hypoxia induced vasoconstriction of pulmonary arterioles which can lead to pulmonary hypertension, right heart failure and cor pulmonale

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8
Q

How can low inspired pO2 lead to hypoxia and how is this compensated?

Example and what are long term solutions?

A
  • People acutely at high altitudes can get mountain sickness
  • Hyperventilation so low pO2 and pCO2
  • Chronic high altitudes compensate by polycythemia, increased capillary density, 2,3 DPG
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9
Q

How can hypoventilation lead to hypoxia?

A

- Type 2 respiratory failure (acute high pCO2 needs urgent ventilation as life threatening)

  • Entire lung poorly ventilated
  • Can fix pO2 by administering oxygen
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10
Q

How do you work out alveolar ventilation?

A

Alveolar volume x Respiration rate

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11
Q

What are some causes of hypoventilation?

A
  • Obesity
  • MD
  • Polio
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12
Q

Why does someone with chronic type 2 respiratory failure not need to be ventilated?

A
  • Compensate, will need to be ventilated as disease progresses though
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13
Q

How do you treat hypoxia in someone with chronic type 2 respiratory failure?

A

Controlled oxygen therapy

  • 24-28% oxygen to achieve sats of 88-92%
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14
Q

Why do you need to give controlled oxygen therapy when a patient has hypoxia with hypercapnia (e.g COPD)

A
  • Correcting hypoxia removes pulmonary hypoxic vasoconstriction so perfusion increased to poorly ventilated alveoli and respiratory stimulus removed
  • Because the pO2 will increase so respiration rate will lower leading to hypercapnia and low blood pH
  • Check bicarb and CO2 over 24-48 hours
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15
Q

How can a V/Q mismatch lead to respiratory failure and how is this compensated?

A

- Reduced ventilation: V/Q<1 in pneumonia, asthma, COPD early, RDS

- Reduced perfusion: V/Q>1 in PE causes diverted blood changing the V/Q elsewhere

Type 1 respiratory failure due to chemoreceptors causing a hyperventilation

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16
Q

Why doesn’t hyperventilation in a V/Q mismatch correct hypoxaemia?

A
  • Because the haemoglobin is fully saturated
  • Does correct pCO2

Type 1 Respiratory Failure (can administer oxygen)

17
Q

What are some causes of V/Q mismatch?

A
  • PE
18
Q

How can a diffusion impairment lead to hypoxia?

A
  • Thick barrier, e.g lung fibrosis and pulmonary oedema
  • Low surface area
  • O2 diffuses less readily than CO2 so this is impaired the most

- Type 1 respiratory failure

19
Q

What are some causes of diffuse lung fibrosis?

A
20
Q

What happens if you give someone with a shunt in the respiratory system oxygen?

A
  • Air can’t get in so makes no difference
  • Need positive pressure ventilation to adjust O2
    e. g RDS there is no surfactant so alveolar atelectasis
21
Q

What is the danger of type 1 respiratory failure?

A
  • Can lead to type 2 e.g asthma exacerbation and end stage COPD
22
Q

What causes of hypoxaemia can be corrected by administration of oxygen?

A

Shunts don’t respond to oxygen

23
Q
A
24
Q

How does the body increase bicarbonate levels when trying to compensate a respiratory acidosis?

A
  • Kidneys retain more
  • PCT makes more from amino acids
25
Q

Why do you still get normal pCO2 in RDS even though there is impaired ventilation?

A

Carbon dioxide is more soluble than oxygen

Respiratory (Revision) (23 decks)

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