Pulmonary.Pulmonary-physiology
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- What is the level of PaO2 below which a patient is said to have hypoxemia?
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E: Hypoxemia usually is defined as a partial arterial oxygen tension (PaO2) < 60 mmHg.
A: 60 - What are the five mechanisms of hypoxemia?
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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 - Which is the most common cause of hypoxemia?
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E: V/Q abnormalities, which are responsive to oxygen therapy.
A: V/Q - How can the five basic mechanisms of hypoxemia be differentiated?
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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% - What happens to the PaO2 when a patient with a diffusion abnormality is given 100% O2 (increases/decreases)?
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E: Increases.
A: I - How are the values of PaO2, PaCO2 and A-aO2 affected at high altitudes?
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E: PaO2 decreases, PaCO2 is normal or decreased, A-aO2 is normal.
A: D,N,N - A patient has low PaO2, high PaCO2 and normal A-aO2. Which basic mechanism accounts for his hypoxemia?
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E: Hypoventilation
A: Hypo - A hypoxemic patient is administered 100% O2 but his PaO2 does not go up. Which basic mechanism accounts for his hypoxemia?
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E: A patient with a shunt will not improve with 100% O2.
A: shunt - What is the range for normal PA-aO2?
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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 - How does aging affect Pa-aO2?
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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 - What is the formula for alveolar-arterial oxygen gradient?
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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). - What is the value normally used for RQ?
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E: Usually a value of 0.8 can be used for RQ, which reflects the normal mixture of dietary substrates.
A: .8