What is a common hemodynamic effect of positive-pressure ventilation?

• A. Increased venous return.
• B. No effect on venous return.
• C. Increased afterload.
• D. Decreased venous return.

Answer: (D)

Positive-pressure ventilation raises intrathoracic pressure during inspiration, which compresses the great veins and the heart’s chambers, making it harder for blood to return to the heart. That lowers preload—the amount of blood filling the ventricles before they contract—so stroke volume and overall cardiac output can fall, especially in patients who are hypovolemic or depend on preload. When the patient exhales, intrathoracic pressure falls and venous return can improve somewhat. This is the most consistent and immediate hemodynamic change with positive-pressure ventilation, more so than any increase in venous return.