Very important and difficult situation in this surgery? (7)
I believe the answer is:
keyhole
'this surgery?' is the definition.
(I've seen this before)
'very important and difficult situation' is the wordplay.
'very important' becomes 'key' (I've seen this before).
'and' means one lot of letters go next to another.
'difficult situation' becomes 'hole'.
'key'+'hole'='KEYHOLE'
'in' acts as a link.
(Other definitions for keyhole that I've seen before include "Aperture in lock - kind of surgery" , "Sort of surgery" , "Aperture for lock opening" , "It provides access to wards" , "Opening in door etc" .)