Ch. 5 West Flashcards
T/F: The alveolar PO2 is largely determined by the level of alveolar ventilation
True
The PO2 of inspired air is, at sea level, with a body temperature of 37*C and a water vapor pressure of about 50 mmHg is _______ mmHg
150 mmHg
Five causes of hypoxemia:
Low inspired FiO2
Hypoventilation
Diffusion impairment
R-to-L shunt
V/Q mismatch
Alveolar PO2 is determined by a balance between the rate of _____ of O2 by the blood, and the rate of ____ of the O2 by alveolar ventilation.
Rate of removal of O2 by the blood
Rate of replenishment of O2 by alveolar ventilation
Based on the relationship between ventilation and CO2 level seen in the alveolar ventilation equation, decreasing the ventilation by 50% will result in the PCO2 _____ under steady state conditions.
Doubling
In the alveolar gas equation, “R” represents the respiratory quotient. Explain what that is.
The respiratory exchange ratio, i.e. the ratio between CO2 production and O2 consumption, which is determined by the metabolism of the tissues in a steady state and varies based on the balance of fuels consumed (carbs, fats, proteins etc.).
Alveolar gas equation
P(AO2) = P(IO2) - [P(ACO2)/R]
Normal value of R is about 0.8
Shows that the normal fall in alveolar PO2 is slightly greater than the rise in PCO2 during hypoventilation
Why does alveolar CO2 take longer to reach equilibrium if a patient goes from hypoventilation to hyperventilation?
Because the body stores of CO2 are pretty high in the form of bicarb and therefore it takes longer to come to equilibrium
T/F: Hypoventilation always increases the alveolar and arterial PCO2
True
T/F: Hypoxemia associated with hypoventilation is rectified by adding additional oxygen to the inspired gas.
True
Why does diffusion limitation rarely cause hypoxemia?
Because the red blood cells spend enough time in the pulmonary capillary to allow nearly complete equilibrium with the alveolar O2.
What does the term “shunt” indicate as pertains to pulmonary circulation?
Shunt indicates that blood is entering the arterial system without having gone through ventilated areas of the lung.
What are two sources of partially oxygenated/unoxygenated blood that is normally re-introduced to the systemic circulation?
Some of the bronchial artery blood is collected by the pulmonary veins after it has perfused the bronchi and its O2 has been partially depleted.
Another source is a small amount of coronary venous blood that drains directly into the LV through the thebesian veins.
In healthy individuals, the normal % shunt that occurs from drainage of the bronchial and thebesian circulation is:
a. 1%
b. 5%
c. 10%
d. 15%
b. 5%
Which of the following is an important feature of a shunt?
a. Provision of 100% oxygen can completely abolish hypoxemia
b. With provision of oxygen, the shunt can be overridden (i.e. the PaO2 experiences a typical linear response to oxygen therapy)
c. Hypoxemia cannot be completely abolished by provision of 100% oxygen, and in general the response to oxygen therapy is poor.
d. Most patients are not oxygen responsive at all.
c. Hypoxemia cannot be completely abolished by provision of 100% oxygen, and in general the response to oxygen therapy is poor.
Hypoxemia cannot be completely abolished by provision of 100% oxygen. The shunt will always continue to depress the PaO2, however the patient may still benefit from oxygen therapy since it will hyper-oxygenate the non-shunted blood and can tip the scale in the patient’s favor. The smaller the shunt, the more oxygen-responsive a patient will be.