Final answer:
The increased C(a-v)O2 from 4.2 to 7.4 vol% after an increase in PEEP suggests reduced cardiac output, as PEEP can affect hemodynamics by decreasing venous return and cardiac output.
Step-by-step explanation:
A patient's C(a-v)O2 has increased from 4.2 to 7.4 vol% after PEEP was raised from 10 to 15 cm H2O. This change suggests that there is a greater extraction of oxygen by the tissues because of a higher differential between arterial and venous oxygen, which is often indicative of reduced cardiac output. Essentially, as the tissues extract more oxygen due to reduced blood flow, the C(a-v)O2 widens. Altered PEEP can affect lung mechanics and hemodynamics, often causing a decrease in cardiac output due to an increase in intrathoracic pressure, which reduces venous return and subsequently cardiac output.
Decreased ventilation generally would not cause an increase in C(a-v)O2, as it would likely lead to both reduced arterial and venous oxygen saturation. Alveolar overdistension typically refers to lung injury due to high PEEP, not directly influencing C(a-v)O2. An increased cardiac index signifies improved cardiac output, which would typically lead to a narrower C(a-v)O2, contrary to the scenario described.