Arterial blood gases tutorial

Question 1

What does the body physiology processes work best at? pH?

Answer 1

Between 7.35 and 7.45

Question 2

What is the most important extracellular buffer systems in the body to maintain control of the pH of the body?

Answer 2

CO2 + H2O HCO3 + H(+)

Question 3

What waste products excretion/retiention controlled by the lung?

Answer 3

CO2

Question 4

For simplicity should CO2 be thought of as an ACID or ALKALI?

Answer 4

ACID

Question 5

Where is Bicarbonate excreted? (HCO3)

Answer 5

Its an alkali excreted/reabsorbed by the kidneys

Question 6

Due to the excretion/reabsorption of HCO3 by the kidney is this a fast or slow process?

Answer 6

ITs a slow process and so the change in concentration due to bicarb is slower than CO2

Question 7

For simplicity should HCO3 be thought of as an ACID or ALKALI?

Answer 7

ALKALI

Question 8

What is compensation?

Answer 8

The body’s own attempt to correct a pH balance

Question 9

How does the body do this? (Compensation)

Answer 9

The body can either rapidly gain or lose CO2 (Acid) or more slowly gain or lose HCO3 (alkali)

Question 10

What can these process do in terms of pH?

Answer 10

They can alter the pH in the right direction but will not return it to normal

Question 11

Is it possible to overcompensate?

Answer 11

It is not possible to overcompensate

Question 12

Describe metabolic acidosis - when does it happen?

Answer 12

IT comes about when there is an excess of H+ produced by the body due to disease (lactic acidosis/renal failure/sepsis)

Question 13

What does the body do in metabolic acidosis?

Answer 13

It tries to counteract the excess H+ and balance the equation by getting rid of the acid - the easiest and fastest way to do this is to get rid of CO2 (CO2 is acid)

Question 14

What happens in respiratory acidosis?

Answer 14

There is an accumulation of CO2 (ACID) due to a disease of the lungs or a problem with the mechanics of respiration

Question 15

How does the body counteract the accumulation of acid in respiratory acidosis?

Answer 15

It tries to hold onto Alkali by reabsorbing bicarbonate from the kidneys (SLOW PROCESS)

Question 16

What would be seen in ACUTE respiratory acidosis?

Answer 16

A reduced pH
Increase in CO2
Little or no change in bicarb

Question 17

What would be seen in more chronic respiratory acidosis?

Answer 17

Increase in HCO3 - as it has accumulated because the kidneys have had time to reabsorb it to try and counteract the CO2

Question 18

What is metabolic alkalosis due to?

Answer 18

A net loss of acid from the body leaving an alkali surplus

Question 19

How does the body counteract the surplus of alkali in metabolic alkalosis?

Answer 19

Tries to hold onto acid by hyperventilating and retaining CO2

(may also vomit - loss of significant amounts of stomach acid)

Question 20

What is respiratory alkalosis due to?

Answer 20

Lack of acid because of the loss of CO2. This arises due to hyperventilation from anxiety, pain, early sepsis etc

Question 21

What does the body to in respiratory alkalosis?

Answer 21

It should lose HCO3 - however this a slow process and the causes of resp alkalosis are usually short lived.

Question 22

What is PaO2?

Answer 22

The partial pressure of O2 in arterial blood.

Question 23

Give the normal ranges of pH, PaO2, PaCO2 and BE?

Answer 23

pH = 7.35-7.45
PaO2 = 9.3 - 13.3 kPa
PaCO2 = 4.7-6 kPa
BE = -2 to +2 mmol/l

Question 24

What does a high PaCO2 indicate?

Answer 24

Respiratory acidosis

Question 25

What does a low PaCO2 indicate?

Answer 25

Respiratory alkalosis

Question 26

How does the body try to compensate for a metabolic acidosis?

Answer 26

by lowering PaCO2 (hyperventilating)

Question 27

How does he body compensate for a metabolic alkalosis?

Answer 27

by raising PaCO2 (hyperventilating)

Question 28

What is Base Excess?

Answer 28

A measure of how much base has to be removed or added to the system to correct the pH in standard conditions. (ie. it assumes a normal CO2)

It is a measure of metabolic acidosis or alkalosis

Question 29

What does a negative BE indicate?

Answer 29

Metabolic acidosis

Question 30

What does a positive BE indicate?

Answer 30

Metabolic alkalosis