A new critical system is on its way that is more involved, chaotic, and engaging to deal with--it's a long-awaited companion for Goonchem.
This new system doesn't apply to all races--station races that do not utilize this new system are Diona, Slime People, and IPC; they will die using the old method of blacking out, slowly accumulating damage, then dying.
Treating people is basically the same as before, with a few nuanced caveats. You apply patches or advanced trauma/burn kits to heal people, you inject them with chems to heal them, you can throw them in cryo to stabilize them.
That said, how people lapse into crit will be fairly different. When your patient hits 0 health, they will lapse into a critical state where they can't see well, their movement can become scrambled, and they fall down a lot. During this time, they can acquire shock. Shock worsens these conditions. If shock is not treated, then the person will start undergoing cardiac failure. Treating shock can be healed by injecting saline or healing the underlying damage and getting their health solidly back into the healthy category. It's recommend you still inject saline as a primary tool, especially if they have heart failure (or you can't treat them in time while you're running to get some other medicines).
Cardiac failure is even worse than shock; it'll become even more difficult to breathe, and if left untreated, will result in full out cardiac arrest. Treating cardiac failure is done with atropine or epinephrine. This condition will not go away by merely curing the underlying damage. You must treat it with atropine or epinephrine. Both chems are equally good at treating it; having both in the bloodstream, at once, increases the chances of treating it.
Finally is cardiac arrest. When acquired, you'll flop on the ground and rapidly take brain and oxygen damage. Treating cardiac arrest can be done with full size defibs or the new handheld defibs. It it strongly recommended you utilize handheld defibs, as they're specialized in treating cardiac arrest.
Death occurs primarily by brain damage; if the brain dies, your patient dies.
A few helpful pointers and tips:
-STOP RELYING ON CRYO. Cryo just heals damage, but doesn't treat the underlying conditions when someone is in a critical state. Time is your enemy under this new system; it's faster and better to apply patches (or advanced burn/trauma kits) or medicine directly to the patient than to throw them in cryo and wait for it to kick in and their body temperature to be low enough. Cryo should be used to stabilize patients who you don't have time to treat, but it shouldn't be the primary treatment method you rely on.
-THERE IS A NEW HANDHELD DEFIB. Hanheld defibs work differently from full size defibs. They do not revive people from the dead. They purely treat patients undergoing cardiac arrest. They can also treat heavy O2 damage, so even if a patient isn't undergoing cardiac arrest, they are still useful for rapidly lowering O2 damage. Full size defibs cannot treat the O2 damage like handheld ones, and have a sizeable delay before activating; it's not recommend you use full size ones unless it's a desperate situation.
-PAY ATTENTION TO YOUR HUD. A frowny green face is indicative of viruses; it could also mean they're in shock or undergoing cardiac failure.
-CPR CAN SAVE A LIFE. CPR has been buffed dramatically under this system. It heals a significant chunk of O2 damage and completely resets the losebreath timer on a patient. In can really help, in a pinch, when someone is in critical condition. Don't expect it to save someone in full out cardiac arrest though.
-Treating patients in deep critical is going to require a broad range of medications. It's strongly recommended you keep saline, epinephrine, mannitol, and salbutamol on you for dealing with deeply critical patients. Handheld defibs can help correct high amounts of O2 damage as can utilizing CPR, but handheld defibs can be unreliable at this task. O2 damage can accumulate incredibly rapidly, leading to a death spiral that will result in the patient's death in no time flat. In some situations, there will be cases where there nothing you can do. Treating a patient's damage is important, but always factor in shock, heart failure, and cardiac arrest into your plan of treating your patient, or else they're going to pay the ultimate price; their death.
I'm sure there's more, but this should help you get a good start and help you treat patients on some level. Feel free to ask me any questions though!