Chapter 5 Flashcards
What are the Four Causes of Hypoxemia?
- Hypoventilation
- Diffusion Limitation
- Shunt
- Ventilation-Perfusion Inequality
What does Hypoventilation do to Alveolar and Arterial Pco2?
- Always increases it
What is Hypoventilation?
- Reduced Breathing frequency
- Reduced Breathing Intensity
What would Hypoventilation do to Po2?
- Decrease unless additional O2 is inspired
How is Hypoxemia easily reversed when it is caused by Hypoventilation?
- Adding O2 to the inspired gas
What is a Shunt?
- Very poorly ventilated alveoli
How does Hypoxemia respond to added inspired O2 when it is caused by a Shunt?
Poorly
- Arterial Po2 does not rise to the expected levels when 100% O2 is inhaled
- Useful diagnostic test
When can the shunt size be calculated?
By the Shunt Equation
- Only if it is caused by mixed venous blood
What is the Ventilation Perfusion Ratio?
- VA/Q
What does the Ventilation Perfusion Ratio Determine?
- THe gas exchange in any single lung unit
What do regional differences in the Ventilation-perfusion ratio of an upright lung cause?
- pattern of regional gas exchange
How does a ventilation-perfusion ratio inequality impair the lung?
- impairs uptake of all gases by lung
- Impairs elimination of all gases by lung
How can an impairment in CO2 elimination due to ventilation-perfusion inequality be corrected? What about Hypoxemia? Explain the reason for the answer.
CO2 correction
- Increasing ventilation to the alveoli
Hypoxemia
- Cannot be corrected by increased ventilation
Reason
- CO2 and O2 have different shaped dissociation curves
What are the two main causes of Hypercapnia?
- Hypoventilation
- Ventilation-perfusion inequality
What is Hypercapnia
- CO2 Retention
What is the only cause of Hypoxemia that is not corrected by giving 100% O2 to breathe?
- Shunt
What is the normal pressure of ambient air at sea level?
- 760mmHg
What is the pressure of water molecules in humidified air? (like in the lungs)
- 47 mmHg
What is the average percentage of oxygen in the air?
- 20.93%
What is the equation for identifying the Partial Pressure of Oxygen in Tracheal Air?
Ota = 0.2093 x (760 - 47)
Ota = 149mmHg
What are the average air pressures of different gasses in alveolar air?
- Oxygen: 14.5%
- Carbon Dioxide: 5.5%
- Nitrogen: 80%
How do you determine Alveolar Partial Pressures of Oxygen and Carbon Dioxide?
Alveolar PO2 = 0.145 x (760-47)
Alveolar PO2 = 103mmHg
Alveolar PCO2 = 0.055 x (760-47)
Alveolar PCO2 = 39mmHg
What does Hypoxemia mean?
- Low PaO2
What happens to a small amount of coronary venous blood?
- Drains directly into the cavity of the left ventricle through the thebesian (in the myocardium) veins
What happens to some Bronchial Artery Blood in a normal lung?
- Collected by the pulmonary veins after it has perfused the bronchi and its O2 has been partially depleted
