Pulmonary.pulmonary-Physiology

Front 1

What is the level of PaO2 below which a patient is said to have hypoxemia?

Back 1

E: Hypoxemia usually is defined as a partial arterial oxygen tension (PaO2) < 60 mmHg.
A: 60

Front 2

What are the five mechanisms of hypoxemia?

Back 2

E: * Decreased inspired oxygen (PiO2): high altitude, nonpressurized airplane cabin.
* Hypoventilation: decreased minute ventilation resulting in increased arterial carbon dioxide (CO2) that leads to hypoxemia. (CNS impairment, respiratory muscle fatigue, or neuromuscular disease).
* Diffusion abnormality: diffuse interstitial pulmonary fibrosis.
* Ventilation-perfusion (V/Q) abnormalities: mismatching of ventilation and perfusion.
* Shunt: perfusion of nonventilated lung (pneumonia, pulmonary edema). Hypoxemia secondary to shunting is refractory to oxygen therapy.
A: FiO2, shunt,V/Q, hypoventilation, diffusion

Front 3

Which is the most common cause of hypoxemia?

Back 3

E: V/Q abnormalities, which are responsive to oxygen therapy.
A: V/Q

Front 4

How can the five basic mechanisms of hypoxemia be differentiated?

Back 4

E: The values of PaO2, PaCO2, alveolar-arterial oxygen (A-aO2) difference, and response to breathing 100% oxygen can be used to separate the basic causes of hypoxemia.

A: ABG, A-aO2, 100%

Front 5

What happens to the PaO2 when a patient with a diffusion abnormality is given 100% O2 (increases/decreases)?

Back 5

E: Increases.
A: I

Front 6

How are the values of PaO2, PaCO2 and A-aO2 affected at high altitudes?

Back 6

E: PaO2 decreases, PaCO2 is normal or decreased, A-aO2 is normal.
A: D,N,N

Front 7

A patient has low PaO2, high PaCO2 and normal A-aO2. Which basic mechanism accounts for his hypoxemia?

Back 7

E: Hypoventilation
A: Hypo

Front 8

A hypoxemic patient is administered 100% O2 but his PaO2 does not go up. Which basic mechanism accounts for his hypoxemia?

Back 8

E: A patient with a shunt will not improve with 100% O2.
A: shunt

Front 9

What is the range for normal PA-aO2?

Back 9

E: A normal Pa-aO2 is usually less than 10 mmHg in a patient breathing room air. In conditions that interfere with gas exchange between the alveoli and pulmonary capillaries, the PA-aO2 increases. In pure hypoventilation, when lung function is not impaired, the Pa-aO2 is normal.
A: 0-10

Front 10

How does aging affect Pa-aO2?

Back 10

E: Oxygenation normally decreases slightly with increasing age. An age-adjusted normal Pa-aO2 can be estimated as follows: 2.5 + 0.21(age). Thus, a healthy 70-year-old is expected to have a Pa-aO2 of approximately 17 mmHg. Of course, this equation yields only an approximation; there may be a great deal of individual variation.
A: Increases

Front 11

What is the formula for alveolar-arterial oxygen gradient?

Back 11

E: the Pa-aO2 can be calculated by using a simplified form of the alveolar gas equation:
PA-aO2 = FiO2*(Patm - pH20) - PaCO2/RQ.
where RQ is the respiratory quotient, FiO2 is the fraction of the inspired gas that is oxygen (21% in room air), Patm is the atmospheric pressure (760 mmHg at sea level), and PH2O is the vapor pressure of water (assumed to be 47 mmHg).

Front 12

What is the value normally used for RQ?

Back 12

E: Usually a value of 0.8 can be used for RQ, which reflects the normal mixture of dietary substrates.
A: .8