Lactulose is synthesized nonabsorbable disaccharide. It is not absorbed in the intestinal tract, and can be decomposed into lactic acid and acetic acid by colonic bacteria, and the pH value of intestinal tract is reduced to less than 6. It can block the absorption of ammonia, reduce the accumulation and absorption of endotoxin, restore the patient's blood ammonia to normal, making the patient turn from coma to sober.