Rodent had got loose inside, causing scene of utter confusion (8)
I believe the answer is:
madhouse
'scene of utter confusion' is the definition.
(madhouse can informally mean any chaotic place)
'rodent had got loose inside' is the wordplay.
'rodent' becomes 'mouse' (mouse is a kind of rodent).
'got loose' indicates an anagram.
'inside' means one lot of letters goes inside another.
'had' with letters rearranged gives 'adh'.
'mouse' going around 'adh' is 'MADHOUSE'.
'causing' is the link.
(Other definitions for madhouse that I've seen before include "state of chaos" , "badly run establishment?" , "asylum" , "pandemonium?" , "9d 21d [BEDLAM]" .)