Low blood pressure in 90-year-olds may be caused by gastrointestinal bleeding, malnutrition, hypothyroidism, heart failure, and heart valve disease, and requires targeted treatment and therapy to slowly return to normal. 1. Gastrointestinal bleeding: 90-year-olds with gastrointestinal bleeding, often resulting in low blood pressure, the need for timely blood transfusion and hemostatic treatment. 2. Malnutrition: 90-year-olds with malnutrition will also have persistently low blood pressure, and should be actively supplemented with proteins, vitamins and other nutrients. 3. Hypothyroidism: When the 90-year-old has hypothyroidism, the metabolic rate of the body will decrease, which will also cause low blood pressure, and should follow the doctor’s instructions to take regular levothyroxine sodium for active treatment. 4. Heart failure: patients with heart failure, the heart contraction ability to decline, may cause low blood pressure, need to consult a doctor in time, for heart failure symptoms and causes of treatment. 5. Heart valve lesions: elderly patients may have degenerative heart valve disease, such as aortic valve stenosis, aortic valve closure insufficiency, sometimes may cause blood pressure, need to consult a doctor in time, improve the heart ultrasound examination, assessment of the condition and the overall situation, if necessary, feasible valve surgery. 90-year-old low blood pressure, must promptly identify the specific causes, usually also need to regularly monitor the situation of blood pressure, once the decline in blood pressure, the need for timely medical treatment.