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Ventilation–Perfusion Relationships and Hypoxemia
10 QuestionsIn an upright lung, which region has the highest ventilation-perfusion (V/Q) ratio?
AApex
BBase
CMiddle
DAll regions have the same V/Q ratio
In a region of the lung, alveolar ventilation is 0.5 L/min and perfusion is 0.2 L/min. Calculate the V/Q ratio and state whether it is high, normal, or low.
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At sea level, a patient has an arterial PCO2 of 40 mmHg and a respiratory quotient of 0.8. Using the simplified alveolar gas equation, calculate the alveolar PO2 (PAO2) in mmHg. Assume FiO2 = 0.21, barometric pressure = 760 mmHg, and water vapor pressure = 47 mmHg.
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Which of the following conditions causes a right shift of the oxygen-hemoglobin dissociation curve?
ADecreased temperature
BDecreased 2,3-DPG
CIncreased acidity (lower pH)
DDecreased carbon dioxide
A patient with hypoxemia receives 100% oxygen, but the PaO2 does not improve significantly. Which of the following mechanisms is most likely responsible?
ALow V/Q mismatch
BTrue shunt
CHigh V/Q units
DIncreased alveolar ventilation
Given the following oxygen content values: capillary oxygen content (CcO2) = 20 mL/dL, arterial oxygen content (CaO2) = 18 mL/dL, and mixed venous oxygen content (CvO2) = 15 mL/dL. Calculate the shunt fraction (Qs/Qt) as a percentage.
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A patient with pneumonia has hypoxemia that does not correct with 100% oxygen. Which of the following best categorizes the underlying mechanism?
AV/Q mismatch due to airway obstruction
BTrue shunt due to alveolar filling
CHigh V/Q units due to pulmonary embolism
DHypoventilation with normal A-a gradient
A patient has hypoxemia. The A-a gradient is elevated. Which of the following is the most likely cause?
AHypoventilation
BV/Q mismatch or shunt
Explain why positive end-expiratory pressure (PEEP) improves oxygenation in a patient with ARDS and describe how monitoring guides therapy adjustment in such a patient.
Short answer