Enema prep for sigmoidoscopy?

My boyfriend might have IBS and he will be having a sigmoidoscopy.

I am concerned about him going through the stimulant laxative and PEG-3550 osmotic laxative, because having intense diarrhea might be hard on his digestive system... also can it disrupt bowel flora through expelling stuff or from the chemicals and osmotic conditions proving detrimental to the bowel flora? I hear of many people developing digestive problems after doing the endoscopy prep. I don't want this procedure to make his digestive problems worse.

I have seen that in some hospitals all that is used for sigmoidoscopy prep is: 1) two Fleet enemas, 1 and 2 hours before the procedure, or 2) nothing, if the patient is not constipated. There are studies comparing these methods with the bisacodyl/halflytely, and they are more or less equivalent.

If the saline from the Fleet is too dangerous or irritating, I'm wondering if even a few enemas (not Fleet phosopo-soda) but just of warm purified water might not be enough.

I'm just wary about the possibility of the procedure prep making his problems worse.

Any thoughts about sigmoidoscopy prep or about the bisacodyl/HalfLytely prep?

I feel so guilty for perhaps messing up his procedure (if the other prep is not enough), but on the other hand I hear the normal prep is awful and can exacerbate or cause digestive problems, so I don't want him to have to go through that unless it's strictly necessary.

I have ulcerative colitis, IBS-D and severe GERD and have had approx. 15 colonoscopies in the past ten years, endoscopy about every other year and, for me, have never had any long term problems from the prep. I hate to add something to your current concerns, but I believe the sigmoidoscopy is a worthless procedure and most MD's (let's say HMOs) do it first b/c it's a much cheaper procedure, but, if the sigmoid doesn't reveal anything then--if your MD is competent--will suggest doing the full colonoscopy--which they just should have done in the first place. A friend of mine suffered an extra six months b/c her GI MD did a sigmoid first, didn't see anything and said she must just have colitis "or something" but it was colon cancer and wasn't detected b/c the sigmoid, as you may not know, does not check the entire colon. I always advise friends to demand the colonoscopy in the first place, the MD will resist, but ask how, if there is cancer in the upper colon area, will the sigmoid detect it if it doesn't go all the way up? It seems to work.