Cheatography
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Ventilation and Gas Exchange
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Key Terms
Alveolar deadspace |
alveolar that are ventilated but not perfused, and where, as a result, no gas exchange occur. |
Deadspace ventilation |
ventilation in excess of perfusion; High V/Q |
Shunt perfusion |
perfusion in excess of ventilation; Low V/Q |
Pathology |
it is the cause and effect of diseases; the typical behavior of a disease |
Example
A 60-year-old, 48-kg woman with a 2-day history of thrombophlebitis of the right calf suddenly complains of chest pain and SOB. While breathing a fraction of inspired oxygen (FI02) of 0.21, the following clinical data are available above.
Result: Acute alveolar hyperventilation (respiratory alkalosis) with mild hypoxemia.
Example (cont)
After 20 minutes of oxygen therapy (FIO2 0.50):
Result: Acute alveolar hyperventilation (respiratory alkalosis) secondary to hypoxemia.
Example (contt)
On further evaluation, this patient was found to have a left lower lobe pneumonia.
If the diagnosis were pulmonary embolus, the following clinical data would have been:
Example (conttt)
The minute ventilation is about three times normal, and yet the PACO2 is only slightly less than normal, suggesting an increased deadspace ventilation.
At 50% inspired O2, there is a significant increase in the PAO2 without significant changes in the ventilatory status – a circumstance that suggests deadspace-producing pathology.
A.
Increase dead space occurs in pulmonary embolism |
Lung areas that are ventilated but not perfused form part of the dead space. Alveolar dead space is potentially large in pulmonary embolism. |
Acute PE impairs the efficient transfer of oxygen and carbon dioxide across the lung (Tables 2). |
Decreased arterial Po2 (hypoxemia) and increase in the alveolar-arterial oxygen tension gradient are the most common gas exchange abnormalities. Total dead space increases. |
Ventilation and perfusion become mismatched, with blood flow from obstructed pulmonary arteries redirected to other gas exchange units. Shunting of venous blood into the systemic circulation may occur. |
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