Breakdown of D'ailleurs, déshydraté, l'enfant s'est évanoui.
être
to be
l'enfant
the child
d'ailleurs
moreover / by the way
s'évanouir
to faint
Questions & Answers about D'ailleurs, déshydraté, l'enfant s'est évanoui.
How does the detached word déshydraté function in this sentence without a verb like 'being'?
This is called a detached adjectival phrase (l'apposition détachée). Even without a linking verb, déshydraté directly modifies the subject, l'enfant. In French, placing an adjective or past participle between commas like this is an elegant way to imply a cause. It translates to 'Because he was dehydrated...' or 'Being dehydrated...'. Remember that it must agree in gender and number with the subject it modifies (here, masculine singular).
How would I rewrite this sentence to state the cause explicitly rather than using déshydraté as a detached participle?
You could use a subordinate clause with a conjunction like comme (since/as) or parce que (because). For example: Comme il était déshydraté, l'enfant s'est évanoui (Since he was dehydrated, the child fainted). The detached participle just offers a more concise, slightly more literary style.
Could I use Par ailleurs instead of D'ailleurs at the beginning of this sentence?
Not without slightly changing the nuance. D'ailleurs (besides, moreover) is typically used to reinforce a point just made, adding a related piece of evidence or an afterthought. Par ailleurs (furthermore, on another note) introduces a completely new, parallel piece of information. Here, the fainting child is likely reinforcing a previous statement about the harsh conditions.
Why does s'est évanoui use the auxiliary verb être?