Invasive blood pressure is measured by inserting one end of a catheter into an artery or vein, or in some cases into the heart chambers, and then connecting the other end of the catheter to a mercury manometer consisting of a U-shaped glass tube, and then reading the blood pressure value at the measurement site on the mercury side of the U-tube. Because of the toxicity of mercury, only the average pressure can be measured. Many patients in critical or shock, or some cardiac surgery and major surgery often use invasive blood pressure, which can monitor real-time changes in blood pressure, which is very valuable in clinical practice. Invasive blood pressure is also used in patients with severe myocardial infarction and heart failure, as well as in patients with severe hypertension and heart disease undergoing major surgery, often using arterial puncture sites for ease of operation and easy observation.