One should always tailor the session to the person being tied and take into account their ability to cope. You should enquire about injuries, or any conditions which may be exacerbated by the activity and make suitable allowances. In my opinion, those with conditions such as heart, breathing problems, blackouts or fits should be extremely careful. If you have any doubts, consult a professional.
Of course you should be aware of your partner's state or mind or any sensitivities. A good bondage session can kick off some surprisingly emotional reactions. Hopefully it'll just be very hot; but it could be meditative, calming, cathartic, or it might even lead to a panic attack. So be ready, and sometimes you might need to just give a bit of extra support and TLC.