PREP 2020 Flashcards
How can you improve arterial saturation in a post-op Glenn patient with overinflated lungs?
Decrease PEEP- this will return lung volumes to FRC and increase PBF
What circumstance would it be disadvantageous to decrease PEEP in a post-op Glenn patient?
When there is pulmonary edema- this will worsen alveolar O2 exchange and worsen saturations
How does increasing minute ventilation in a post-op Glenn patient effect saturation?
Decrease saturation
-Increased minute ventilation will decrease pCO2, which causes cerebral vasoconstriction, which causes reduced cerebral blood flow which results in decreased return of venous flow through the Glenn which causes desaturation
What are the 2 terms that describe the quantity and relationship of O2 in the blood?
Content
Saturation
How is O2 content expressed?
mL of O2 per 100mL blood
How is oxygen saturation (SaO2) expressed?
Percentage of binding sites on Hgb that are occupied by O2
Healthy individuals with no lung disease breathing room air at sea level have SaO2 between what?
96-98%
What factors affect the O2 content of blood?
PO2
Ventilation and perfusion mismatch
Hgb affinity for O2
Concentration of Hgb
When normally saturated Hgb is circulated to tissues, what % of bound O2 is delivered to the tissues?
25%
What is the typical systemic venous saturation returning to the right side of the heart ?
75%
What is the difference in the saturation of blood leaving the aorta and returning to the right heart?
a-vO2 difference
With normal CO/metabolic demand and no other shunting, what is the average a-vO2 difference?
25 points
What causes a decreased systemic venous saturation and widened a-vO2 differenve?
- Increased metabolic demand- tissues may require more O2 than normal
- If heart unable to upregulate output to meet the demand, tissues will extract more O2 from Hgb than normal leading to a decreased systemic venous saturation and widened a-vO2 difference
What happens to the saturation of Hgb returned from the lungs in the setting of lung pathology (pulmonary edema, PNA, etc)?
Can be decreased
-Ability of the alveoli to transfer O2 to pulmonary arterioles is limited
In the setting of lung pathology, what plays a key role in the determination of the SaO2?
Partial pressure of O2 (O2 tension)
What represents the partial pressure when gases are mixed?
Sum of the pressures that each gas in the mixture exert if alone
When a mix of gases comes into contact with a membrane across which they can diffuse, what is the rate of diffusion dependent upon?
Relevant gradient of the partial pressure of the gas across the membrane (not the concentration of the gas)
True or False: Concentration and partial pressure have a direct relationship in the gas phase?
True
Why is blood able to carry large concentrations of O2?
Hgb high affinity for O2
How do increases in mean airway pressure or addition of supplemental O2 lead to an increase in arterial O2 saturation?
By increasing alveolar partial pressure of O2
How does positive airway pressure improve alveolar O2 tension?
Recruits collapsed alveoli
What can help to increase alveolar O2 tension in regions of low ventilation?
Supplemental oxygen
Lung pathology (pulmonary edema or PNA) can lead to what?
Pulmonary venous desaturation
What measures can improve pulmonary venous and systemic saturation?
- Increasing airway pressure
- Supplemental O2
*Both can increase alveolar O2 tension, improve diffusion and improve pulmonary venous and systemic saturation