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Respiratory Medicine > Acute/Chronic Respiratory Failure > Flashcards

Acute/Chronic Respiratory Failure Flashcards

1
Q

What is type I respiratory failure?

A

pO2<8kPa with a normal or low pCO2

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2
Q

What are the causes of type I respiratory failure?

A
  1. Low inspired o2 - EG high altitudes
  2. V/Q mismatch
  3. Diffusion barrier impairment - Thicker in fibrosis, longer in pulmonary oedema, lower SA in emphysema
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3
Q

What is V in V/Q mismatch?

How do you work out V?

A 
Amount of air reaching alveoli in a given amount of time
RR x (tidal volume - anatomical dead space)
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4
Q

What is Q in V/Q mismatch?

A

Flow of blood through the pulmonary capillaries surrounding the alveoli

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5
Q

What does V/Q<1 mean?

What happens as a consequence?

A

There is inadequate ventilation of some alveoli (shunt)

Pulmonary capillary pO2 will be low, so vasoconstriction of pulmonary arterioles occur.

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6
Q

What conditions cause V/Q<1?

A

Early asthma and COPD
RDS in newborns
Anatomical shunts (V/Q=0) - Blood supply goes from artery to veins without passing capillaries
ARDS

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7
Q

What does V/Q>1 mean?

A

Poor perfusion to a lung segment (anatomical dead space)

Alveolar pCO2 will be low, so bronchoconstriction occurs

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8
Q

What conditions cause V/Q>1?

A 
Pulmonary embolism (V/Q=infinity)
Cardiovascular shock
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9
Q

Why is CO2 normal in type I respiratory failure?

A
  1. CO2 is more soluble than O2 in blood

2. CO2 does not need a carrier molecule

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10
Q

What is type II respiratory failure?

A

pO2<8kPa and a high PCO2>6.5kPa

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11
Q

What are the causes of type II respiratory failure?

A

Hypoventilation

Acute

  • Respiratory centre depression in head injury/drug overdose
  • Airway obstruction - very severe acute asthma

Chronic

  • Respiratory muscle weakness
  • Mechanical problems eg scoliosis
  • Hard to ventilate lungs eg COPD
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12
Q

What happens in acute type II respiratory failure?

A

Severe hypoxia and hypercapnia which is life threatening

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13
Q

What happens in chronic type II respiratory failure?

A

Compensatory mechanisms develop which allow better toleration of hypercapnia and hypoxia

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14
Q

What investigations would you do if a patient presents with respiratory failure?

A

Bloods - aBG, FBC, U+E, LFT, CRP
Radiology - CXR
Microbiology - Blood and sputum cultures if febrile
Spirometry

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15
Q

What is the immediate management of type I respiratory failure?

A
  • Treat underlying cause
  • Give oxygen (24-60%) by facemask
  • Assisted ventilation if PO2<8kPa despite 60% O2
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16
Q

What is the immediate management of type II respiratory failure?

A
  • Treat underlying cause
  • Controlled O2 therapy - starting at 24%
  • Recheck aBG after 15 minutes, if pCO2 is steady or lower increase O2 to 28%. If pCO2 risen >1.5kPa, consider assisted ventilation if patient still hypoxic
17
Q

Why do you give chronic type II respiratory failure patients controlled oxygen?

A
  • Hypoxia drives respiratory effort

- If hypoxia is reduced, respiratory drive from peripheral chemoreceptors will reduce also which worsens hypercapnia

18
Q

What are some symptoms of acute hypoxia?

A
  • Dyspnoea
  • Restlessness
  • Agitation
  • Confusion
  • Central cyanosis
19
Q

What are some effects of chronic hypoxia?

A
  • Hypoxic vasoconstriction of pulmonary vessels - leads to pulmonary hypertension, then cor pulmonale, then right sided heart failure
  • Polycythaemia - increased viscosity of blood
20
Q

What are some symptoms of acute hypercapnia?

A
  • Headache
  • Peripheral vasodilation
  • Bounding pulse
  • Tachycardia
  • Bounding pulse
  • Tremor/flap
  • Papilloedema
  • Confusion
  • Drowsiness
  • Coma
21
Q

What are some compensatory mechanisms of chronic hypoxia?

A
  1. Increased EPO secreted by kidney to raise Hb
  2. Increased 2,3-DPG to shift Hb dissociation curve to the right
  3. Increased capillary density in tissues
22
Q

What are some compensatory mechanisms of chronic hypercapnia?

A
  1. Renal compensation of respiratory acidosis (loss of HCO3-)
  2. Central chemoreceptors - choroid plexus imports HCO3- into CSF so reset to a new higher CO2 level. More CO2 is needed to create respiratory drive.
  3. Respiratory drive now driven by hypoxia
23
Q

Where are the peripheral chemoreceptors?

What stimulates them?

A
  • In carotid body (cnIX)
  • In aortic body (cnX)
    Response to changes in pCO2, pO2 and pH
24
Q

Where are the central chemoreceptors?

What stimulates them?

A
  • In the ventral surface of the medulla of the brain

Respond to pCO2 only

Respiratory Medicine (14 decks)

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