What Is the Best Single Measure of Effective Ventilation in the Intensive

What is the best single measure of effective ventilation in the intensive care unit patient?

A) dead space-tidal volume ratio
B) PaCO₂
C) end-tidal PCO₂
D) $\dot { \mathrm { Q } } _ { s } / \dot { \mathrm { Q } } _ { t }$