problem that can occur when the colon absorbs excess fluid and sends it to the circulatory system. 2 tsp of salt per L of H2O in enema preparation reduces the risk. Water from a cleansing enema and barium enema can be shifted from the colon into the circulatory system, increasing blood volume. Fluid overload is pulmonary edema, seizures, coma and death. Observe pt for changes in mental status, apathy, drowsiness - indicators of onset of hypervoleumia. Sedative premedication is contraindicated for lower GI exams for this reason.