Thats a tricky one really ...
Only idea I have is you have one or two bars 'pain' and 'stamina' ... trying to break free will slowly increase the pain bar, if it goes to high you pass out/die so you can't constantly struggle and need to rest. Stamina would be how much energy you can put into struggling at any one go ... so its sort of resource managment style mechanic, you need to keep your pain meter in check while making the best use of your stamina. Maybe a third meter for bondage/hold strength.
Controls
A/D = Struggle, lite escape attempt, can loosen bondage/hold for a strain attempt.
W = Strain, heavy but painful escape attempt.
S = Tense, receive less pain from 'attacks' but don't recover stamina as fast.
Space = Recover, suck in breath to refill stamina meter, but extra vulnerable to attacks.
X = Adrenaline, maybe a sort of 'nitro' ability, get 3 uses and allows you to take immense amount of pain, after it wears off stamina bar drops greatly, also have to be careful for when it wears off as you might go above your pain threshold.