Arterial Blood Gases And Acid Base Regulation

Question 1

How do you calculate pH?

Answer 1

Question 2

What is an acid?

Answer 2

Any molecule that has a loosely bound H+ ion that it can donate

Question 3

What is a base?

Answer 3

An anionic (negatively charged) molecule capable of reversibly binding protons (to reduce the amount that are ‘free’)

Question 4

Describe corrective compensation

Answer 4

Changes in ventilation can stimulate a RAPID compensatory response to change CO2 elimination and therefore alter pH
Changes in HCO3- and H+ retention/secretion in the kidneys can stimulate a SLOW compensatory response to increase/decrease pH

Question 5

What is the difference between acidaemia and acidosis?

Answer 5

Acidaemia - qualitative evaluation of the pH of the blood
Acidosis - circumstances that are creating a change where the blood pH is falling

Question 6

What is the normal blood pH range?

Answer 6

7.35-7.45

Question 7

Outline the interpretation procedure

Answer 7

• Type of imbalance (acidosis, alkalosis, normal)
• Aetiology of imbalance (e.g. respiratory, metabolic, mixed)
• Any homeostatic compensation (un-/partially/fully compensation)
• Oxygenation (hypo-/normo-/hyperoxaemia)

Question 8

What is the normal range for base excess?

Answer 8

-2 to 2

Question 9

Outline the levels of oxygenation

Answer 9

Severe hypoxaemia - <6 kPa
Moderate hypoxaemia - 6-8 kPa
Mild hypoxaemia - 8-10 kPa
Normoxaemia - 10-13.5 kPa

Question 10

What is the typical PCO2 range?

Answer 10

4.7 to 6.4 kPa