A very high mean airway pressure can cause which of the following hemodynamic consequences?

• A. Increased venous return and cardiac output
• B. Decreased venous return and increased cardiac output
• C. Decreased venous return and decreased cardiac output
• D. No effect on hemodynamics

Answer: (C)

When mean airway pressure is very high, intrathoracic pressure rises, which impedes blood returning to the heart. That reduced venous return lowers the preload (the filling of the ventricles), and because the heart has less blood to eject, stroke volume and overall cardiac output fall. In some cases, the elevated intrathoracic pressure can also increase resistance in the pulmonary vasculature, adding to the right ventricle’s workload, further diminishing output. The net result is decreased venous return and decreased cardiac output.