Sounded like ARDS when you described it at the beginning. The ICU nurses are also fonts of knowledge/translation or at least a good resource for sorting on the confusing "docterace" language you get so don't be afraid to ask them. Also the increase pressure for ventilation could be causing some vagal nerve stimulation, kind of like bearing down to take a crap and you feel your pulse kind of drop and get a little light headed. The vagal nerve runs through the thorax and increased pressures there could cause increased pressures on that nerve. Good luck to her. Good luck to you. Be sure to get a little quiet, reflective time for yourself, so you can recharge your own batteries. When My wife had appendix cancer it was amazing how much it took out of me for a 6m to a year. Good luck!