A 67-year-old man with metastatic prostate cancer is admitted to the ICU for treatment of deep venous thrombosis and pulmonary embolism. His oxygen saturation on admission is 90%. Blood gas analysis reveals a Pao2 of 60 mm Hg and a Paco2 of 60 mm Hg. A random sample of expired gas is evaluated, and the mean exhaled Pco2 is 30 mm Hg. Please calculate the ratio of dead space to tidal volume (VD/VT).
A. 30%
B. 40%
C. 50%
D. 60%
E. FiO2 is needed to calculate VD/VT