The metabolic imbalance definitely seems feasible here, especially when you also consider that the body can also attempt to "correct" these imbalances via diarrhea instead of vomitting, or sometimes both. I say that because isn't it a fairly common thing that people often poop right before death (not sure how common)? I've heard this referred to as "losing control" over one's bowels, I guess inferring that total loss of muscle (spincter) control (given the total ATP depletion perhaps?) is the culprit. But, when I stop and think about that, that really does not make sense because a person would still have to have some energy reserves to poop because peristalsis is required for pooping, even with mere spinal reflexes.
Thus, the idea of bowel obstruction also does not seem too off the mark - maybe not necessarily 'obstruction' per se, but perhaps very lazy bowels (which can have a nauseating effect) due to the amount of pain meds given to someone 'circling the drain' (not to mention the toxic effects of drug metabolites built up from high dosages/frequencies in combo with a very compromised metabolism). So, it makes sense that it could be RT a combo of all of the above. Just some thoughts...
Afterthought...nervous tissue is highly sensitive and so a metabolic disturbance could surely upset the vomitting center in the brain.
Not sure why I'm feeling so tangential right now....sorry..., but here is the real answer (I think?)...I just looked again at your title and keyed in on the word "projectile". If it was truly "projectile" and not just "regular vomitting", it makes sense that it would HAVE to be ICP-related. How can you be sure that there were no mets to the brain? Hospice patients don't usually go for a lot of tests. Of course, I've also seen the dx. Metabolic encephalopathy too...no sure what the patho is behind that...does the brain become edematous and if so, how much?
I will ask my fiance (he is a GI doc) if he has known of any "strictly GI cases" with 'projectile' vomitting - I'm curious to know if this is soley an ICP-related thing.
Sorry again for the digression...I really loved patho back in school...wish I had time/motivation to read it more
Sorry, one last thought and I will shut up...Maybe you could tell the family members that such a phenomenon is purely "reflexive" and go on to liken this to a knee jerk reflex or something...it's sudden and appears "violent", but that actively dying patients do not "feel" things (like hunger) the way we do...i.e. it's likely not the horrible feeling of nausea the way we feel it.
BTW, hospice nurse really are angels!