Severe hyperglycemia can lead to neurological symptoms and even coma. The causes of hyperglycemia leading to coma include the following: First, diabetic ketoacidosis, when blood sugar rises significantly a large amount of glucose is excreted from the urine, the body can use less carbohydrates and can only carry out lipolysis to supply energy, and ketone bodies are the products of lipolysis. Ketone bodies are highly acidic substances, and diabetic ketoacidosis will occur when ketone bodies accumulate in excess, and severe diabetic ketoacidosis will lead to coma and even death. Second, hypertonic coma, when the blood glucose level is too high easily lead to high blood osmolarity, more than the regulatory mechanism of brain cells, hypertonic coma. Hyperosmolar coma is mostly seen in elderly patients, and the mortality rate of hyperosmolar coma is higher than that of diabetic ketoacidosis. Third, lactic acidosis, mostly seen in patients with diabetes combined with cardiac and pulmonary insufficiency and those taking large amounts of metformin. When diabetic patients with markedly elevated blood glucose, combined with cardiac and pulmonary insufficiency make lactic acid production increase, which can lead to lactic acidosis and coma in serious cases.