Effects of v/q inequality on paco2 and paco2 Flashcards
What is the primary effect of V/Q inequality on PaO₂?
Decreased PaO₂ (Hypoxemia):
• V/Q mismatch leads to reduced oxygenation of blood in low V/Q areas. • Low ventilation relative to perfusion results in less oxygen being delivered to the blood.
Why does V/Q inequality cause hypoxemia?
• Areas with low V/Q ratios (e.g., pneumonia, atelectasis) have poor ventilation and cannot effectively oxygenate blood.
• High V/Q areas cannot compensate for low V/Q areas, resulting in hypoxemia (low PaO₂).
What happens to PaCO₂ in mild to moderate V/Q mismatch?
PaCO₂ remains normal or slightly elevated:
• The body compensates for poor CO₂ elimination in low V/Q areas by increasing ventilation in other lung regions. • CO₂ diffuses more easily than O₂, allowing for better compensation.
What happens to PaCO₂ in severe V/Q mismatch?
PaCO₂ increases (Hypercapnia):
• In severe V/Q mismatch, the ability to compensate through increased ventilation is overwhelmed, leading to elevated PaCO₂.
What are clinical examples of a low V/Q ratio?
• Pneumonia, pulmonary edema, atelectasis:
These conditions result in well-perfused but poorly ventilated areas, causing hypoxemia (low PaO₂) and potentially elevated PaCO₂ if compensation fails.
What are clinical examples of a high V/Q ratio?
• Pulmonary embolism:
Ventilated but poorly perfused areas lead to dead space ventilation and a slight reduction in PaO₂. PaCO₂ is often normal due to compensatory hyperventilation.
How does the body compensate for V/Q inequality?
• Hypoxic pulmonary vasoconstriction: Diverts blood flow from poorly ventilated areas to well-ventilated areas.
• Hyperventilation: Increases CO₂ elimination in well-ventilated areas, helping maintain normal PaCO₂ levels.
What is the impact of V/Q inequality on gas exchange?
• PaO₂ decreases due to impaired oxygenation in low V/Q areas.
• PaCO₂ may remain normal or rise, depending on the severity of the mismatch and the body’s compensatory mechanisms.
