on my unit we would use BIS only if the patient was paralyzed and sedated. We had a scale if they were on sedation only as far as awake and calm, awake and agitated, easily arousable, etc. but if somebody is paralyzed that is not going to work, so we would slap a BIS on them to make sure they were not awake underneath the paralyzation. As far as it ranging from the 60s to 90s I'm not sure, we would occasionally experience a smaller drop or rise and would just adjust the sedation accordingly. At least on our monitors a quality indicator number would pop up alongside the bis, so if that read between 90-100 we knew our BIS was accurate, if it was low you would need to try pressing down on the pad areas where it is reading and also think about changing out the whole set, that should be changed at least every 24 hours.