Hypoxia, Resp Failure and ARDS

Question 1

What are the 4 types of hypoxia?

Explain each briefly

Answer 1

1. Hypoxaemic - poor oxygenation by lungs
2. Anaemic hypoxia - low Hb, but each is fully saturated
3. Circulatory hypoxia - poor tissue perfusion, but O2 content of blood normal
4. Cytotoxic - tissues cannot use O2

Question 2

What is the definition of respiratory failure?

Answer 2

PaO2 < 8kPa

Question 3

What is type 1 respiratory failure?

Answer 3

PaO2 < 8kPa, PaCO2 normal or low

Question 4

Give some examples of what might cause type 1 respiratory failure

Answer 4

Either V/Q mismatching, or diffusion defects - e.g.

• PE
• Emphysema
• Severe asthma
• ARDS
• Pulmonary oedema
• Pulmonary fibrosis

Question 5

How would you manage type 1 resp failure?

Answer 5

Treat underlying cause
Give O2 35 - 60%
If PaO2 still under 8kPa despite 60% O2, NIV

Question 6

Define type 2 resp failure

Answer 6

PaO2 < 8kPa and PCO2 > 6kPa

Question 7

What causes type 2 respirator failure? Give some examples

Answer 7

Ventilatory failure
E.g. 
Chronic pulmonary disease e.g. COPD, asthma
Low resp drive e.g. opioids
Neuromuscular e.g. MND
Thoracic wall disease e.g. flail chest

Question 8

How should you manage type 2 resp failure?

Answer 8

If acute - ventilation - only way to get rid of excess CO2
If chronic:
- Controlled O2 therapy - start at 24%
- Repeat ABG after 20 mins. If CO2 is stable or falling, increase O2 to 28%.
- If PaO2 still low and PCO2 rising, consider NIV or I+V

Question 9

Why must you keep sats between 88 and 92% in chronic type 2 resp failure?

Answer 9

2 reasons:

1. Increasing O2 worsens V/Q mismatching
2. Hypoxia drives respiration, so increasing O2 lowers resp drive

Question 10

Briefly outline the pathophysiology of ARDS

Answer 10

Can occur through direct lung injury or secondary to severe systemic illness.
Lung damage and release of inflammatory mediators causes increased capillary permeability, and hence non-cardiogenic pulmonary oedema.

Question 11

List 3 signs of ARDS

Answer 11

• Cyanosis
• Tachycardia/tachypnoea
• Peripheral vasodilatation
• Bilateral fine inspiratory crackles

Question 12

In brief outline, how would you manage ARDS?

Answer 12

Admit to ITU
Resp support - usually I+V
Circulatory support
Treat any sepsis
Nutritional support