Infusion of potassium chloride with hardened blood vessels is usually due to phlebitis. When infusing fluids, if the drugs with relatively high irritation are inputted, such as antibiotics, chemotherapeutic drugs, hypertonic solutions, highly concentrated fluids, etc., it is easy to induce phlebitis. Potassium chloride solution is relatively irritating to the blood vessels, which may lead to phlebitis, and once phlebitis occurs, the localized area will be red, swollen and painful, and due to the stimulation of the inflammation, the blood vessels will be hardened, and the localized area will be painful with pressure. The incidence of phlebitis can be reduced by infusing irritating drugs such as potassium chloride solution slowly and evenly. Specific treatment should be prescribed by a physician.