The pace alternates a lot during chapter 22 and I think it is slowed down mainly due to the distance Amir creates between himself and the story.
He creates a distance in one way by using the phrases in itallics to foreshadow events such as "surgical cap". This phrase has no relevance to the current position or place Amir is in, and perhaps shows us that something is going to happen to him in order for him to end up in hospital ------> surgical cap. Surgery.
Also even though Amir tells the story of his and Assef's fight in graphical detail it lacks greately in any serious emotion. He is reciting it but not creating any sence of his emotion at the time whatsoever.
The only thing he repeats or that we get a sence that he feels/notices is "sohrab screaming". This obviously holds emotive context and the repetittion shows significance of the caring emotions Amir holds towards Sohrab.