One removing last of haemoglobin from large vessel (5)
I believe the answer is:
taker
'one removing' is the definition.
(someone who removes or takes things)
I can't explain the remainder of the clue.
(Other definitions for taker that I've seen before include "(Challenge) acceptor" , "Person accepting an offer" , "He accepts" , "Could be a thief" , "one's prepared to bet" .)