 The entire procedure often takes 4 to 6 hours.Often patients vomit (especially if ipecac was given prior to the procedure or following ingestion of a drug that produces vomiting such as aspirin or theophylline), indicating that the rate of infusion may need to be slowed or an antiemetic such as metoclopramide given.Major gastrointestinal dysfunction precludes the use of whole bowel irrigation.