Lost vital fluid, swallowing new mix (5)
I believe the answer is:
blend
'mix' is the definition.
(I know that mix can be written as blend)
'lost vital fluid swallowing new' is the wordplay.
'lost vital fluid' becomes 'bled' (I am not sure about this - if you are sure you should believe this answer much more).
'swallowing' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'bled' placed around 'n' is 'BLEND'.
Can you help me to learn more?
(Other definitions for blend that I've seen before include "Mix, stir" , "Amalgam" , "Coalesce" , "Mix together" , "Thorough mixture" .)