First anaesthetised individual - absorbing hospital drama (6,3)
I believe the answer is:
'first' is the definition.
('number one' can be a synonym of 'first')
'anaesthetised individual absorbing hospital drama' is the wordplay.
'anaesthetised individual' becomes 'numbone'.
'absorbing' means one lot of letters goes inside another.
'hospital drama' becomes 'er'.
'numbone' enclosing 'er' is 'NUMBER ONE'.
(Other definitions for number one that I've seen before include "top-selling record" , "the most important person" , "top man?" , "Informally and numerically, oneself" , "it concerns egoists" .)