The old cliche, "the operation was a success, but the patient expired," may well have had its origin in the experience of surgeons losing patients due to biochemical derangements after performing a technically successful gastrointestinal surgical procedure. Diseases of the gastrointestinal tract that result in obstruction, perforation, fistula formation, or severe diarrhea and vomiting often are first seen with marked water, electrolyte, and acid-base imbalances that must be corrected before surgery. Additionally, the biochemical consequences of altering the continuity of the gastrointestinal tract by creating artificial stoma, removing diseased portions of the gut, or bypassing segments of small and large bowel can be formidable. Thus, the surgeon often must deal with complicated electrolyte and metabolic disturbances before he can apply his surgical skills, and the surgical procedure he performs may result in additional problems. These factors emphasize that the biochemical status of the patient, before as well as after surgery