Monster Auras

Quick question what is the aura that high level monster use that
when you get close to them a lot of life gets drain from you?

Sadly, I've never heard of such an aura. I can think of two things that might be killing you:

1. Some monsters - mostly nears and some Unique map bosses - have an aura that deals chaos damage over time. These should be quite easily manageable with any kind of recovery, such as life leech, life regeneration, life flasks, life leech, etc.

2. Corrupting Blood is a damage over time mechanic that can be very deadly when not prepared against. It is not an aura. A monster with Corrupting Blood or Corrupted Bloodline mod will add 1 charge of Corrupting Blood on you each time it hits you and each time you hit it. This means if you deal many Hits very quickly you will take greater and greater damage over time.

Corrupting Blood is considered a bleeding effect and as such can be cured and prevented against using flasks of Staunching, which is a magic flask mod that removes all bleeding and prevents bleeding during flask effect.