This is the same as a regular bandage.
Your bind wound skill determines how high you can bandage and how many points you get per bandage. Bandaging stacks with any spell or item regen that you have including your base standing regen.
From skill 1 to 200 you can bind up to 50% health and you get skill/4 hps per bandage. So at 200 skill you get 50 hps per bandage. The last bandage can take you over 50% health but can't be applied once you reach 50% (I would often get a message that I couldn't bind wounds past 50% at 47% to 49% which is quite annoying.) If you start to apply the bandage before 50% and your regen takes you too high before it finishes it will also fail if I remember correctly.
At skill 201+ you can bandage to 70% (20% higher than before) and the skill/hp ratio improves to skill/2.5 so you get an immediate jump from 50hps to 80.4 (I don't recall if it rounds up or down) hps per bandage. if you are a class that gets up to 210 skill you will cap out at 84 hps per bandage.
First Aid AA skill adds 10% per level, up to 30%, to the max health you can bandage but not the points per bandage. You can get up to 80% with 50 hp bandages at 200 or up to 100% at 201+ with 80+ hp bandages.
If you have an item with a bind wound skill modifier that takes your skill over 200 you will get the additional 20% and the improved hp ratio as long as you have the item equipped. With a skill item and AA points it is possible for a character that normally caps at 200 skill (50%, 50hp bandages) to bandage to 100% with 80+ hp bandages.