Oxygen Therapy and Respiratory Failure

Question 1

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

Answer 1

• Type 1 Respiratory Failure: Lack of oxygen

* Type 2 Respiratory Failure: Lack of oxygen and too much carbon dioxide due to ventilation falling.

Question 2

Name four factors that put you at risk of developing type 2 respiratory failure

Answer 2

• COPD
• Cystic Fibrsosis
• Kyphoscoliosis
• Morbid Obesity

Question 3

Explain the V/Q mismatch and how giving oxygen can cause type 2 respiratory failure?

Answer 3

• Areas of poor ventilation have reactive vasoconstriction
• Giving excess oxygen revereses that reactive vasoconstrtiction
• Perfusion becomes good, but ventilation is still poor so CO2 can’t get out despite more oxygen going in. CO2 will then go back into the blood.

Question 4

In relation to the haldane effect explain how giving more oxygen can result in type 2 respiratory failure

Answer 4

O2 can displace CO2 from Hb so giving the patient more oxygen results in CO2 being released into the blood.

Question 5

Explain hypoxic drive theory

Answer 5

• Normal respiration driven by CO2 chemoreceptors
• Chronic hypercarbia leads to desensitisation of these receptors
• Oxygen chemoreceptors then become the primary drive for respiration instead of carbon dioxide.
• This theory is actually true for very few patients.

Question 6

How to treat hypercarbia?

Answer 6

• Ensure conservative oxygen management (SaO2 88 – 92 %)

* Increase Vminute (RR is usually already high) but can Increase VT with NIV

Question 7

4 types of hypoxia?

Answer 7

Circulatory hypoxia
Anaemic hypoxia
Toxic hypoxia
Hypoxaemic hypoxia

Question 8

6 causes of alveolar hypoventilation?

Answer 8

• Opiates cause respiratory depression by suppressing the central nervous system
• Laryngeal obstruction can be caused by anaphylaxis, or physical obstruction
• Obesity causes hypoventilation by stenting the diaphragm, preventing diaphragmatic excursion inferiorly, reducing tidal volume, and lung volumes
• Bronchial obstruction (in this case a pea) can cause distal collapse
• Anaesthesia – the drugs reduce respiratory effort, having a tube in the airway restricts airflow, paralysis prevents normal respiratory effort, artificial ventilation is not as good as natural respiratory effort. The longer the anaesthetic the worse it is for the patient, in many ways.
• Kyphoscoliosis (very severe in this case) reduces respiratory excursion, and can cause type 1 and type 2 respiratory failure.

Question 9

4 situations with evidence you can use unrestricted oxygen therapy?

Answer 9

Cluster headaches, carbon monoxide poisoning, pneumothorax not treated with a chest drain, and sickle cell crisis.