Mannitol is hypertonic and can cause irritation to the endothelium of blood vessels, triggering an inflammatory response in the endothelium. Endovasculitis occurs and even causes blood clots to develop in the lining of the blood vessels, also called thrombosed superficial phlebitis. In this case, the blood vessels will become hard, swollen, painful, and the surrounding skin will be red, and the cords can be detected under the skin. In this case, hot compresses or physical therapy can be used to promote the absorption of local inflammation, and topical medications, such as Xiliao Tou or sodium heparin ointment, can be applied to reduce the inflammatory reaction and relieve pain. If pain symptoms are severe, non-steroidal anti-inflammatory drugs such as ibuprofen or diclofenac sodium can also be administered orally, which can provide significant pain relief. To prevent this, the site of the infusion can be changed, while other fluid supplements should be given intravenously after the infusion of mannitol to reduce the irritation of the blood vessels by mannitol.