HISM index problem

I want make a crowd with HISM, and make every one of them have HP, can be damaged and destroy.
I made a map/dict with int key(instance index) and float value(HP), but as you said, the index of HISM is not “stable”, the index of HISM won’t point to the same instance, btw, I got the index from hit result->hit item . how can I fix it, or HISM can still works for me ?