DSA 2: Respiratory Adaptations Flashcards
How do you calculate alveolar oxygen levels?
Alveolar O2 (PAO2) = Inspired Oxygen - Oxygen consumed
How do you calculate inspired oxygen?
PiO2= (Patm - 47 mm Hg)x FiO2
How do you calculate oxygen consumed?
Oxygen Consumed = [PaCO2/RQ]
What is the normal respiratory quotient?
0.8
What respiratory quotient for those who are using an IV glucose solution?
1
What respiratory quotient for those who are hypoglycemic?
0.7
What is the proper way to calculate alveolar oxygen levels?
Alveolar O2 (PAO2) = [(Patm - 47 mm Hg)x FiO2] - [PaCO2/RQ]
Under normal/ideal conditions, the alveolar oxygen and the arterial oxygen should be at ______.
Equilibrium
-consider <12 mm Hg normal
If alveolar oxygen and the arterial oxygen are not in equilibrium, what does that mean?
Diffusion Impairment
- COPD
- Pneumonia
- Interstitial Fibrosis
What is the V/Q ratio?
Balance between:
Ventilation: bringing oxygen into alveoli and removing CO2 from the alveoli
Perfusion: removing O2 from the alveoli and adding CO2
What happens when V/Q ratio is decreased?
- Alveolar (and therefore arterial) levels of oxygen will decrease
- CO2 levels will increase
What happens when V/Q ratio is increased?
- Alveolar (and therefore arterial) levels of oxygen will increase
- CO2 levels will decrease
During hypoventilation, what happens to the alveolar/arterial gradient?
Stays the same
- Hypoventilation has nothing to do with the alveolar barrier itself
- A-a O2 gradient only increases when the process of gas exchange is impaired somehow - meaning that what happens at the alveolar barrier is impaired.
When we stand up, do we see a higher or lower V/Q ratio?
Lower: more blood reaches base of lung while less air reaches there
What is a physiological shunt?
Blood travelled to the lungs, it didn’t get any oxygen
What is an anatomical shunt?
Blood physically doesn’t enter the lungs
What is hypoxic vasoconstriction?
Low V/Q ratio:
- blood coming into the area will be directed to other parts of the lung.
- decreasing the perfusion of the hypoxic region will raise the V/Q ratio and bring the arterial blood gases closer to what we expect
What is bronchoconstriction?
High V/Q ratio:
- bronchi will constrict slightly to increase the resistance and decrease the amount of ventilation coming into an area that is not well perfused (although it won’t shut it down entirely).
- limits the amount of alveolar dead space that occurs and minimizes the ‘wasted’ work that occurs with alveolar dead space.
What is hypoxia?
Inadequate oxygen available for use by the tissues
What is hypoxemia?
Low oxygen content in the blood
What is hypoxic hypoxia?
PaO2 is below normal because:
- alveolar PO2 is reduced (e.g environmental reasons such as altitude)
- blood is unable to equilibrate fully with the alveolar air (e.g. as would occur in lung diseases with diffusion impairments such as emphysema or fibrosis)
What is anemic hypoxia?
Lungs are in perfect working condition, but the oxygen carrying capacity of the blood has been reduced.
- Carbon Monoxide: it binds to the Hb with high affinity, preventing oxygen from binding and reducing the oxygen carrying-capacity of blood
- Tissues do not get sufficient oxygen to maintain their metabolic needs because the blood is not carrying it.
What is circulatory hypoxia?
Lungs are fine and the blood can carry sufficient oxygen, but the tissue is not receiving sufficient oxygen
-Heart cannot pump the blood to the tissue (or arteries
blocked)
-Sickle cell anemia: cells sickle in the blood vessels and block them. (also produces an anemic hypoxia)
What is histotoxic hypoxia?
Lungs, blood, and circulatory system are all fine but tissue cells are poisoned and cannot use oxygen
- Cyanide: poisons systems that utilize oxygen to create energy and preventing them from using the oxygen
- Plenty of oxygen there but cells experience a lack of oxygen
