Arterial Blood Gases & Acid Base Regulation

Question 1

What is meant by “Pulmonary circulation”? what type of blood does it carry?

Answer 1

the system of transportation that shunts de-oxygenated blood from the heart to the lungs to be re-saturated with oxygen before being dispersed to the body (back into the systemic circulation)
- Carries mixed venous blood

Question 2

What is the “systemic circulation”? what type of blood does it carry?

Answer 2

carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body
- oxygen-rich blood

Question 3

What is meant by “pulmonary transit time”?

Answer 3

Amount of time blood has for gas exchange

Question 4

What is the equation for pH?

Answer 4

𝑝𝐻=−〖𝑙𝑜𝑔〗10 [𝐻+]

Question 5

How do you work out H+ conc?

Answer 5

[H+]= 10-pH

Question 6

What is an acid?

Answer 6

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

Question 7

What is a base?

Answer 7

A base is an anionic (negatively charged ion) molecule capable of reversibly binding protons (to reduce the amount that are ‘free’)

Question 8

What is the difference between respiratory acid and metabolic acid?

Answer 8

The pCO2 determines whether an acidosis is respiratory or metabolic in origin. For a respiratory acidosis, the pCO2 is greater than 40 to 45 due to decreased ventilation. Metabolic acidosis is due to alterations in bicarbonate, so the pCO2 is less than 40 since it is not the cause of the primary acid-base disturbance

Question 9

Describe the process of CO2 transport from tissues to the blood

Answer 9

• tissues produce CO2 as a waste product from respiration C6H1206 -> H20 + ENERGY (releases CO2)
• in the tissues PCO2= 6.1kPa
• Blood arrives via arteries at pH= 7.40
  PCO2= 5.3 kPa
• CO2 moves into the blood
• CO2 + H20 -> H2CO3
  H2CO3 -> HCO3- + H+
• blood is more acidic

Question 10

How does the blood react to the decrease in pH caused by CO2?

Answer 10

The blood has an enormous buffering capacity that can react almost immediately to imbalances = COMPENSATION

Question 11

Describe how respiratory alkalosis/ acidosis corrected vs metabolic?

Answer 11

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

An acidosis will need an alkalosis to correct
An alkalosis will need an acidosis to correct

Question 12

What are the types of imbalances you can have in the blood?

Answer 12

Acidosis (or acidaemia) / Alkalosis (or alkalaemia)

Question 13

What are the different causes for blood imbalances?

Answer 13

• Respiratory (acidosis or alkalaemia)
• Metabolic (acidosis or alkalosis)
• Mixed (respiratory and metabolic)

Question 14

What type of compensation can you have to blood imbalances?

Answer 14

Uncompensated / Partially compensated / Fully compensated

Question 15

How can you describe how the oxygenation changes in the blood from imbalances?

Answer 15

Hypoxaemia / Normoxaemia / Hyperoxaemia

Question 16

How do you report an arterial blood gas measurement?

Answer 16

Step 1. Assess the pH (if low, acidosis, if high, alkalosis)
Step 2. Assess the PCO2 (determine if it is a resp or metabolic cause)
Step 3. Assess the BE “base excess” (again to help determine if resp or metaboliv)
Step 4. Assess the PO2 (if compensated or not)