life-and-death 
adjective
Deciding whether someone lives or dies; vitally important: heart surgeons deal with life-and-death situations on a daily basis...
- Data availability is important in medical situations where life-and-death decisions are based on the most-current data.
- Firefighters say this would mean removing vital crew from the specialist appliances needed for life-and-death situations.
- But this may be an acceptable inconvenience, considering the life-and-death importance of a functional alarm.
Synonyms
vital, of vital importance, crucial, critical, urgent, pivotal, momentous, of great moment, important, all-important, key, serious, grave, significant, decisive, far-reaching, historic, weighty, consequential, of great consequence, epoch-making, apocalyptic, fateful, portentous
informal earth-shattering, world-shattering, earth-shaking, world-shaking