Single enhancing lesion points more towards lymphoma than toxo. Toxo is usually multi-ring enhancing lesions.
Hypercarbia causes cerebral vasodilation. If you have ever seen an intra- or acute post-op neurosurgical patient, or really any patient about to herniate, you can remember this because they will be hyperventilated to pCO2 around 25-30 to decrease ICP via cerebral vasoconstriction; in this case, we have the opposite. The curve of pCO2 vs cerebral blood flow is quite steep in the physiologic range meaning small changes in ventilation make a significant difference in CBF.