Acid base regulation******

Question 1

Define Alkalaemia

Answer 1

Refers to high-than-normal pH of blood

Question 2

Define Acidaemia

Answer 2

Refers to lower-than-normal pH of blood

Question 3

Define Alkalosis

Answer 3

Describes circumstances that will decrease [H+] and increase pH

Question 4

Define Acidosis

Answer 4

Describes circumstances that will increase [H+] and decrease pH

Question 5

What is the equilibrium equation?

Answer 5

H2O + CO2 -H2CO3 H+ + HCO3-

Question 6

What is the Pitts and swan experiment and what did they find out?

Answer 6

Dog is anaesthetised. Baseline blood is drawn and it was pH= 7.44.
Dog was injected with 14 molar acid and they expected pH to be 2.5 and so dog to die but it didn’t

Question 7

what does Pitts and Swan experiment show?

Answer 7

The blood has an ENORMOUS buffering capacity that can react almost IMMEDIATELY to imbalances

Question 8

What are the 2 sources of acid?

Answer 8

• Respiratory acid: CO2

- Metabolic acid: pyruvic acid, lactic acid, all other acids that are not CO2

Question 9

what is the ratio which the acids are produced?

Answer 9

Respiratory acid: metabolic acid

100: 1

Question 10

What is sorensen

equation?

Answer 10

To calculate pH from proton concentration (or vice versa)

𝑝𝐻=−Log10[H+]

Question 11

What is henderson equation?

Answer 11

To calculate the dissociation constant (Ka)

K= [H+][HCO3-]/ [CO2][H2O]

Question 12

what is Henderson-Hasselbalch equation

Answer 12

Combines the above equations

pH= pK + Log10 [HCO3-]/[CO2]

Question 13

What is the normal pH for arterial blood

Answer 13

7.40

Question 14

What is the normal pH for venous blood

Answer 14

7.36

Question 15

What is the normal CO2 flux?

Answer 15

For every 100 mL of blood that goes through the systemic capillaries, 4mL of CO2 is added.

therefore:
4 mL/dL/min

Question 16

What is the cardiac output in Litres?

Answer 16

5L

Question 17

What is the basic partial pressure of oxygen guidelines?

Answer 17

Basic guidelines for PaO2

> 10 kPa is normal
8-10 kPa is mild hypoxaemia
6-8 is moderate hypoxaemia
<6 kPa is severe hypoxaemia

Question 18

What can we tell from an ABG?

Answer 18

Is a low blood pH acidosis or acidaemia?
[H+] only? You’d better convert!
Is the PaCO2 normal, high or low?
This is assessing the respiratory component
Is the BE excess high or low?
This is assessing the metabolic component
Is the patient hypoxaemic?
No, mildly, moderately or severely?

Question 19

what are the compensatory mechanisms?

Answer 19

• 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 20

What does an acidosis and an alkalosis need?

Answer 20

An acidosis will need an alkalosis to correct

An alkalosis will need an acidosis to correct

Question 21

What causes a rise/fall in base excess?

Answer 21

A rise in base excess is due to:

• an increase in renal excretion of acid, ingestion/administration of a base or loss of acid from vomiting.
• The result is a metabolic alkalosis.

A fall in base excess is due to:

• the overproduction of metabolic acids, the ingestion of acid, a reduction/failure of acid excretion by the kidney or excessive loss of alkali from intestines with diarrhoea.
• The result is a metabolic acidosis