Final breath or the last possible moment (4-4)
I believe the answer is:
last-gasp
(Other definitions for last-gasp that I've seen before include "Final breath or done at the last possible moment of effort" , "Done in desperation at the final moment" , "'Final breath (4,4)'" , "Final exhalation before death" , "Done in desperation (or at the point of death?)" .)