What great ?'s .. in all the years I've been dealing with reflux I have never happened upon your question about the cabin pressure ... so I don't know but if you are able to repost your ? to the Dr. Expert Forum a physcian who handles the Gerd (Acid Reflux) ?'s may very well, inded be able to help you.
http://www.medhelp.org/forums/show/200
In regard to your other ? I am only a mom and not qualified to really tell you what is best but it a) cannot hurt to go given he is a preemie with reflux .... does he have any signs of micro aspriation/asthma or other breathing issues? If you have a Pulmo under your wing he will MAKE SURE that they know about his breathing issues .... they will be certain you don't give any liquids for aboslutely certain so as not to have any issues with reflux while being put out.
My son at age 12 weeks had to have a bowel resection and did fine for his surgery .. I, like you, was VERY concerned about the reflux and being put out .. moreso than the surgery to remove a large duplication intestinal cyst he was born with. Today he is a thriving 9 yr old boy!
Oftentimes when our refluxers are gaining wt. they don't get the proper attn of the Peds .... because they are not failure to thrive .. this is a tough one to battle so trust your instincts.
One last ? .. did they say he will probably outgrow this as it is weak muscles due to being born early? My son's was immature GI tract and after 2.5 yrs he became alomst relfux free!
Hope this helps! WELCOME to this great community!
Cheryl