I would wonder if perhaps his pain is due to his muscles, etc, not getting enough oxygen. Lack of oxygen affects our whole body and every organ needs it. I, too, agree that he should be talking with his doctor regarding his oxygen levels of low 70's. Are they below 90 during the day? Do they drop when he is more active? It is my understanding when the levels are below 90, it may be he needs oxygen 24/7. IMO, one thing he should not be doing is stopping his use of oxygen with readings that are so low.
Hope he feels better!
I don't know about oxygen regarding pain reduction but if he is dropping into the 70's at night, then he should be using his O2 with CPAP. He would probably feel a whole lot better. I would talk to the doctor about his pain though, perhaps something else is going on that needs to be addressed.
Jenn