Respiratory failure

Question 1

Below what pO2 and O2 saturation is hypoxaemia?

Answer 1

<94% or pO2 <9.3 kPa

Question 2

define respiratory failure

Answer 2

impairment in gas exchange causing hypoxia, with or without hypercapnia

Question 3

What is the difference in ABG results between type 1 and type 2 respiratory failure?

Answer 3

type 1= low pO2 and normal or low pCO2

type 2= low pO2 with high pCO2

Question 4

Give 5 causes of type 1 respiratory failure?

Answer 4

• pneumonia
• ARDS
• pulmonary fibrosis (localised)
• asthma
• COPD
• pneumothorax
• PE
• obesity
• pulmonary hypertension

Question 5

Give 4 causes of type 2 respiratory failure

Answer 5

• SEVERE asthma and COPD
• Drug OD
• CNS injury
• muscle disorders (muscular dystrophy)
• neuromuscular disorders (myasthesia gravis)
• head injuries
• severe obesity, kyphoscoliosis
• pneumothorax, very large pleural effusions

Question 6

What effects does hypoxia have on the body?

Answer 6

• impairs CNS function causing confusion and irritability
• Central and peripheral cyanosis
• cardiac arrhythmias
• hypoxic vasoconstriction of pulmonary vessels

Question 7

What is the normal ventilation/ perfusion ratio?

Answer 7

1
ventilation = 0.35L x 15= 5L/ min
perfusion= 0.07L x 7bpm= 5L/min also

Question 8

If the V/Q ratio drops, what will be the effect on pO2 and pCO2?

Answer 8

pO2 drops

pCO2 rises

Question 9

When does type 1 respiratory failure occur and how does it lead to low pO2 but normal pCO2?

Answer 9

When some alveoli are poorly ventilated/ perfused or diffusion cannot occur, you get a drop in pO2 in the vessels supplying this area. This causes hypoxic vasoconstriction, which directs blood to better perfused areas and also hyperventilation. This directs the blood to good alveoli which will be hyperventilating and blowing off more pCO2, this compensates for the build up of CO2 at the poorly perfused/ ventilated alveoli. The hyperventilating good alveoli cannot compensate fully for the bad alveoli meaning overall pO2 drops, but pCO2 is normal.

Question 10

How do diffusion defects lead to type 1 resp failure?

Answer 10

CO2 is more soluble so can easily diffuse out, but pO2 isnt very soluble so cannot diffuse in. This is the picture seen in interstitial lung disease/ diffuse lung fibrosis due to asbestos, coal work ect.

Question 11

How can a baby with respiratory distress syndrome go from type 1 to type 2 resp failure?

Answer 11

• Normally in ARDS only part of the lung is deficient in surfactant but can affect whole lung if very new (and so cause type 2) or the baby may tire as they cannot keep up the hyperventilation, meaning the pCO2 starts to increase and pO2 decreases further

Question 12

Why can asthma attacks go from t1 to become t2 resp failure?

Answer 12

It can get worse to start to affect the whole lung?

Question 13

What is the general pathophysiology to type 2 resp failure?

Answer 13

Decreased ventilation to whole/ most of lung, pO2 falls and pCO2 rises in the alveoli as air isn’t being moved, meaning the pO2 and pCO2 in the blood fall and rise respectively also.

Question 14

Give 2 examples of diseases when more than one mechanisms are working to cause t1 resp failure

Answer 14

• Pulmonary odema- diffusion defect and less ventilation

- lung fibrosis- diffusion defect and stiffening= poorer ventilation

Question 15

In chronic t2 respiratory failure (eg COPD, severe obesity, kyphscoliosis, interstitial lung disease), you get compensation, what is this?

Answer 15

• increased EPO and so RBC
• increased 2,3 BPG to offload O2 better at tissues
• HCO3- production in kidneys
• hyperventilation
• HCO3-production in CFS to reset central chemoreceptors

Question 16

Why should you not give high flow O2 to someone with COPD?

Answer 16

Because normally, detection of CO2 by central chemoreceptors is what drives breathing. But theirs have reset to accept a high level of CO2 as normal. But their peripheral chemoreceptors are detecting hypoxia and this is what is now driving breathing (hypoxic drive), giving O2 will take away their respiratory drive, cause hypoventilation and worsen their hypercapnia and hypoxia.

Question 17

What should be given to someone with COPD to aid breathing?

Answer 17

• low flow O2 to target saturations at 88-92%

- monitor CO2, if it rises, give ventilator support

Question 18

What effects does hypercapnia have on the body?

Answer 18

Resp acidosis, impairs CNS- drowniess, confusion, headache, coma, warm hands and bounding pulse as causes vasodilation, cerebral vasodilation= headache