Adrenaline fires when you are nearly dead. On a piece that carries it it reads: Below 35% health you gain +{value}% Critical Damage for 5 s, once every 10 s.

Word for word it is Below 35% health you gain +{value}% Critical Damage for 5 s, once every 10 s, and the number in it grows with the gear: 30 to start, 1.5 more for every item level.

0 bases carry it.