I think the key to this may be what was the scan for. If you're suspecting acute small bowel obstruction then you would not generally give an oral bolus (guidelines suggest it's basically a waste of time). If it was more specifically to look at suspected obstruction of the stomach from the Lap Band then I'd argue for a Fluroscopic exam where the oral contrast can be given and live images of it's progress obtained. But if that's not practical then a small volume of oral contrast might be reasonable to try and distend the stomach a little if it appears clinically safe to do so (i.e. she's not vomiting); I don't think I'd be too focused on a generic protocol such as a Bariatric one in such a case.

But if this was for a "general CT abdomen" - for arguments sake, for a suspected mass, and the Lap Band is just a "co-existing condition" - then the overall volume should be near the same as normal - somewhere around 900ml say, split over 30mins or an hour. You wouldn't need a specific "bariatric protocol" in terms of volume, although the patient would likely need to take more time drinking the contrast. The aim of oral contrast in a CT Abdomen (whether "positive" bright white contrast, or "negative" water only) is to try to distend the stomach and bowel so that it can be better assessed it. In a Lap Band case the overall volume of the whole stomach is not massively reduced from a normal patient, but the band has significantly reduced the Fundal proportion so the patient feels full much more easily; that then passes into the rest of the stomach and then fill the rest of the bowel. In practice it will take longer than normal to pass through, taking longer to fill the body of the stomach before passing into bowel. It's probably a good idea to split it into smaller boluses for patient comfort and perhaps spread it out over a longer period than normal too. It may also be practical to cut down the overall volume if it's all taking too long. But in terms of safety, I can't see a good reason to cut it down drastically - 360mls for example is not great if you want to properly assess the bowel.

I'm no expert on Roux-en-Y (and we don't see many at my Hospital) but in such patients the volume of the stomach remnant/pouch is much reduced (to the order of 20mls I think?) and most of the stomach is completely bypassed. Perhaps the contrast regime you've been taught about for Roux-en-Y is more a practical consideration for this? Especially if this regime for patients immediately post op? If so then the focus could be more about not overly distending or irritating a fresh Roux-en-Y pouch, particularly if there is suspected complication. It would be interesting to hear from someone more familiar about Roux-en-Y imaging about this, but I can say I wouldn't personally apply such a regime to every patient with a Lap Band.