Arterial blood gases and acid base regulation

Question 1

What is FiO2?

Answer 1

the conc. of inspired oxygen- room air = 21%

Question 2

What stimulates a rapid compensatory response to a change in pH?

Answer 2

lungs! changes in ventilation- altering CO2 elimination and so pH

Question 3

How do you interpret an ABG?

Answer 3

• type of imbalance: acidosis, alkalosis or normal–> look at pH
• aetiology of imbalance: respiratory acidosis/alkalosis, metabolic acidosis/alkalosis, mixed (respiratory and metabolic- CO2 and BE in opposite directions), or normal
• homeostatic compensation: uncompensated, partially compensated, or fully compensated
• oxygenation: hypoxaemia, normoxaemia, or hyperaemia

Question 4

What might cause a metabolic acidosis?

Answer 4

• loss of bicarbonate e.g. watery faeces

- H+ gain e.g. inc. lactic acid production

Question 5

How would you correct a metabolic acidosis physiologically?

Answer 5

hyperventilation
–> dec. CO2–> equation shifts to correct this, causing more H+ and HCO3- to combine–> to eventually normalise pH , leaving a low CO2 and BE

Question 6

What might cause a metabolic alkalosis?

Answer 6

vomiting–> loss of H+–> pH inc., as well as BE, as less H+ to combine with

or other things that would cause H+ loss or HCO3- gain

Question 7

How would you correct metabolic alkalosis physiologically?

Answer 7

hypoventilation–> inc. CO2