Typically trocar needles can be retained for three to five days, with a maximum of seven days. The cannula needle, also called indwelling needle, is a catheter that is left in the vein using an injection needle, thus reducing the pain caused by repeated venipuncture to the patient, alleviating the anxiety of the family, and at the same time facilitating the clinical use of medication, especially for acute and critically ill patients. If the time is too long, the local veins will be stimulated by the catheter for a long time, thus forming phlebitis, which will result in local redness, swelling, pain and other symptoms.