ABG Basics

Question 1

How do you work out if the patient is hypoxic?

Answer 1

A normal PaO2 on room air is >10kPa.
If the patient is on oxygen, the PaO2 should be ~10kPa less than the % inspired concentration FiO2
E.g. On 2L/min via nasal specs = 24% FiO2, therefore PaO2 should be ~14 kPa

Question 2

What % inspired concentration FiO2 do the common delivery methods of oxygen provide?

Answer 2

Nasal specs:
- 2 L/min = 24%
- 3 L/min = 26%
- 4 L/min = 36%
Non-rebreathe:
- 10-15 L/min = 60-90%
Venturi masks:
- Blue, 2-4 L/min = 24%
- White, 4-6 L/min = 28%
- Yellow, 8-10 L/min = 35%
- Red, 10-12 L/min = 40%
- Green, 12-15 L/min = 60%

Question 3

Type I respiratory failure =

Answer 3

hypoxia + normocapnia

Question 4

Type II respiratory failure =

Answer 4

hypoxia + hypercapnia

Question 5

Why does hypercapnia cause acidosis?

Answer 5

Co2 + H20 = H2CO3 (carbonic acid)