Causes of hypoxaemia and hypercapnia

Question 1

Explain the respiratory exchange ratio

Answer 1

The respiratory exchange ratio= the relationship between CO2 elimination and O2 consumption
-main determinant of RER is the particular metabolic substrate being used

Oxidation of carbohydrates:
C6H12O6 + 6O2 ——> 6CO2 + 6H20

Oxidation of fatty acids:
C6H32O2 + 23O2 ——> 16CO2 + 16H20

Question 2

What are causes of hypoxaemia

Answer 2

Reduced Oxygen in the Air:

Breathing air with a lower concentration of oxygen. This can happen at high altitudes.
Problems with Breathing (Hypoventilation):

Not breathing deeply or frequently enough. This can be caused by:
Conditions affecting the brain’s control of breathing (e.g., drug overdose, brainstem injury).
Conditions affecting the nerves or muscles involved in breathing (e.g., muscular dystrophy, Guillain-Barré syndrome).
Severe obesity (obesity hypoventilation syndrome).
Problems with Gas Exchange in the Lungs (Diffusion Impairment):

The oxygen can’t easily move from the air sacs (alveoli) in your lungs into the blood. This can be due to:
Thickening or damage to the membranes between the alveoli and capillaries (e.g., pulmonary fibrosis).
Mismatch Between Airflow and Blood Flow in the Lungs (Ventilation-Perfusion Mismatch):

Some parts of your lungs might be getting air but not enough blood flow, or vice versa. Common causes include:
Pneumonia (inflammation and fluid in the alveoli).
Pulmonary embolism (blood clot in the lung).
Chronic obstructive pulmonary disease (COPD).
Asthma.

Shunting:

Blood passes through the lungs without picking up oxygen. This can happen with:
Certain heart defects.
Severe lung conditions where alveoli are filled with fluid or collapsed.

Question 3

What are causes of hypercapnia

Answer 3

Causes of hypoventilation that can lead to hypercapnia include:

Conditions affecting the brain’s respiratory center (e.g., drug overdose, brainstem disease).
Problems with the nerves and muscles of breathing (e.g., spinal cord injury, neuromuscular diseases).
Chest wall abnormalities that restrict breathing (e.g., kyphoscoliosis).
Airway obstruction (severe asthma, COPD exacerbation).
Sometimes, hypercapnia can occur with certain lung diseases even if the overall breathing rate isn’t dramatically reduced, due to the lungs’ inability to effectively eliminate CO2