We should wait til Swatsurgeon or Doc T chime in with the REAL expert opinion on this issue of oral rehydration for trauma.... however, I have a thought or two that might not have been considered in this thread.
Along with the already mentioned contraindications about potential vomiting during intubation and/or aspiration risks during intubation...
With a patient who presents with penetrating abdominal wounds, one constant that will be encountered in one form or another with this patient is some degree of shock. The physiology involved in shock causes an initial sympathetic nervous system discharge which leads to aggressive vasoconstriction of the GI arterioles. This causes a significant decrease in blood flow to the GI area. This limits the amount of the resuscitation fluids that can readily diffuse into the circulatory system.
Another factor seen in patients in later stages of shock is generalized cellular deterioration which includes a diminished ability to actively transport ions across the cell membranes. This is important as this active transfer of ions through the gut wall facilitates the isosmotic diffusion of h20 across the gut wall and into the circulatory system. Without this active transport process, H20 is not as easily or quickly absorbed as the chime inside the intestines would have a higher osmolarity than in the circulatory system in that area. This would prevent diffusion of water into the circulatory system.
When you get both these factors working together, it decreases the benefit of giving PO fluids to a severe trauma patient, especially when you weigh in the contraindications.
Course', I could be wrong as the physiology is rarely as simple as I describe in the above. Let's wait and here from some of our trauma experts.