How does pneumonia precipitate acute chest syndrome?

Pathoma says that its because pneumonia causes vasodilation of pulmonary circulation which causes decreased blood flow, increased RBC transit time, then says that causes RBC dehydration, acidemia, and deoxygenation. How does increased transit time of RBC in the pulmonary circulation cause deoxygenation? Shouldn't it be the opposite? Thanks for any help!
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums