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Respiratory > Session 5- Respiratory Failure > Flashcards

Session 5- Respiratory Failure Flashcards

1
Q

what is respiratory failure

A

impairment of gas exchange causing hypoxaemia with or without hypercapnia- may be acute or chrinic condition

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2
Q

type 1 resp failure

A
  • low PaO2 < 8kPa or O2 saturation <90% breathing room air at sea level
  • pCO2 normal or low
  • gas exchange is impaired at the level of alveolar-capillary membrane
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3
Q

type 2 resp failure

A
  • Low pO2 AND high PaCO2 > 6.5kPa breathing room air at sea level
  • Reduced ventilatory effort or inability to overcome increased resistance to ventilation entore lung
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4
Q

hypoxaemia

A

low pO2 in arterial blood

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5
Q

hypoxia

A

o2 deficiency at tissue level

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6
Q

normal o2 saturation

A

94-98%

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7
Q

what does central cyanosis indicate

A

hypoxaemia- occurs when the level of deoxygenated haemoglobin in teh arteries is below 5g/dL with o2 sats below 85%

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8
Q

where is central cyanosis seen

A

oral mucosa
tongue
lips

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9
Q

what is the main cause of hypoxaemia

A

ventilation:perfusion mismatch

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10
Q

what compensatatory mechanisms increase oxygen delivery and therefore decrease hypoxia

A
  • increase EPO by kidney to raise Hb
  • increase 2,3 DPG - shifts curve to the right so o2 is released more freely
  • increased capillary density
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11
Q

what are the consequeces of chronic hypoxic vasoconstriction of pulmonary vessels

A

pulmonary hypertension
right heart failure
cor pulmonale

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12
Q

what happens when V:Q RATIO IS <1

A
  • PaO2 is low
  • PaCo2 rises unless there is compensatory hyperventilation then it will be low or normal
  • Hyperventilation induced by peripheral chemoreceptor firing secondary to hypoxaemia
  • if lung disease severe hypervetilation may nor be able to compensate for V:Q <1
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13
Q

What happens when V:Q > 1

A
  • PaO2 rises and PaCo2 falls
  • resdistribution of pulmonary blood flow
  • blood is redirected to unaffected areas
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14
Q

how is Co2 affected by an increase in diffusion distance

A

CO2 is more soluble there fore Co2 diffusion is lessaffected then diffusion of O2

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15
Q

what type of resp failure do diffusion impairing diseases lead to

A

type 1

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16
Q

what is shunt in respiratory system

A

blood that enters the lung but doesnt take part in gas exchange

17
Q

what is ARDS

A

acute resp disress syndrome

18
Q

pathophysiology of ARDS

A

massive widespread inflammation which damages teh alveoli and results in oedema increased vascular permeability, loss of surfactant and fibrin exudation

results in loss of the hypoxic pulmonary vasoconstriction mechanism and compliance decreases as lungs become stiff and lung volume decreases which creates an intrapulmonary shunt as blood cant get perfused

19
Q

what does hypoventilation cause

A

alveolar pO2 falls-> arterial pO2 falls - hypoxaemia

alveolar pCO2 rises-> arterial pCO2 increases -> hypercapnia

type 2 respiratory failure

20
Q

what can cause acute hypoventilation

A

opiate overdose
head injury
very severe acute asthma

21
Q

what can cause chronic hypoventilation

A

severe COPD

22
Q

how does kyphoscolisosis affect ventilation

A

causes disordered movement of the chest wall- respiratory system compliance reduced in kyphoscoliosis primarily due to the reduction in chest wall compliance and to a lesser degree a reduction in ling compliamce due to miscroatelectasis

23
Q

effects of acute hypercapnia

A

respiratory acidosis

impaired CNS function - confusion, drowsiness, coma, flapping tremors

peripheral vasodilatation - warm hands, bounding pulse

cerebral vasodilatation- headache

24
Q

effects of chronic hypercapnia

A

respiratory acidos compensated by retention of HCO3- by kidney

acclimation to CNS effects - CSF pH normalised

vasodilatation mild but may present

25
Q

how does chronic CO2 retension effect central chemoreceptors

A
  • CO2 diffuses into CSF- CSF pH drops and stimulates central chemoreceptors
  • low CSF pH corrected by choroid plexus cells which absorb (HCO3-) into CSF
  • the CSF pH returns back to jormal ans the chemoreceptors are no longer stimulated
  • PaCO2 is still high but central chemoreceptors now unresponsive to this- if PaCO2 goes higher the reset value central chemoreceptors will fire
26
Q

how can treating hypoxaemia worsen hypercapnia

A

correction of hypoxia removes pulmoney arteriole hypoxic vasoconstriction

  • leads to increased perfusion of poorly ventilated alveoli
  • diverting blood away from better ventilated alveoli- worsen V:Q mismatch

haldene mechanism
-oxygenated Hb cant carry as much CO2 with oxygen CO2 dissociated from Hb into blood

27
Q

what type of resp failure does V/Q mismatch cause

A

type 1

- low pO2 but normal or low pCO2

Respiratory (21 decks)

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