Arterial Blood Gases and Acid Base Regulation

Question 1

What is PO2?

Answer 1

partial pressure of oxygen > indicates how much oxygen is dissolved in the arterial blood

Question 2

What is PCO2?

Answer 2

partial pressure of carbon dioxide > indicates how much CO2 is dissolved in arterial blood

Question 3

What is pH?

Answer 3

‘power of hydrogen’ > describes the acidity, neutrality or alkalinity of the blood

Question 4

What is HCO3-?

Answer 4

plasma bicarbonate > describes the concentration of bicarbonate dissolved in arterial blood

Question 5

What is base excess?

Answer 5

describes the concentration of bases (predominantly bicarbonate) compared with the ‘expected concentration’

Question 6

Describe blood gases in the arteries.

Answer 6

O2: >10kPa/>95%
CO2: 4.7-6.0kPa

Question 7

Describe blood gases in the veins.

Answer 7

O2: 4-5.3kPa/~75%
CO2: 5.3-6.7kPa

Question 8

What is the gas exchange time?

Answer 8

0.25s

Question 9

What is the pulmonary transit time?

Answer 9

0.75s

Question 10

What is an acid?

Answer 10

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

Question 11

What is a base?

Answer 11

an anionic (negatively charged ion) molecule capable of reversibly binding protons

Question 12

Changes in what can stimulate a rapid compensatory response to alter pH?

Answer 12

ventilation

Question 13

Changes in what can stimulate a slow compensatory response to alter pH?

Answer 13

HCO3- and H+ retention/secretion in the kidneys

Question 14

An acidosis needs what to correct?

Answer 14

alkalosis

Question 15

An alkalosis needs what to correct?

Answer 15

acidosis

Question 16

What is the interpretation procedure for an ABG?

Answer 16

type of imbalance: acidosis/alkalosis?
aetiology: respiratory/metabolic?
any homeostatic compensation?
oxygenation?

Question 17

What is the relationship between pH and proton concentration?

Answer 17

inversely proportional

Question 18

What is a potential cause of respiratory acidosis?

Answer 18

hypoventilation

Question 19

What is a potential cause of respiratory alkalosis?

Answer 19

hyperventilation

Question 20

What is a potential cause of metabolic acidosis?

Answer 20

diarrhoea

Question 21

What is a potential cause of metabolic alkalosis?

Answer 21

vomiting

Question 22

How to compensate for respiratory acidosis?

Answer 22

tubular cells reabsorbing more HCO3 from the tubular fluid, collecting duct cells secreting more H+

Question 23

How to compensate for respiratory alkalosis?

Answer 23

reducing the amount of new HCO3− generated and by excreting HCO3−

Question 24

How to compensate for metabolic acidosis?

Answer 24

hyperventilation to decrease the arterial pCO2

Question 25

How to compensate for metabolic alkalosis?

Answer 25

hypoventilation to increase retention of CO2