The American Society of Anesthesiologists (ASA) classifies patients into 5 classes prior to anesthesia based on their physical condition and risk for surgery: Class I: Normal health. No systemic disease except for local lesions. Class II: Mild or moderate systemic disease. Grade III: with severe systemic disease and limited daily activities, but not incapacitated. Grade IV: with severe systemic disease, incapacitated and life-threatening. Grade V: Patients with critical illnesses and life-threatening conditions. If it is an emergency surgery, mark “Emergency” or “E” in front of one of the above levels. Grade Ⅰ and Ⅱ patients have good tolerance for anesthesia and surgery and undergo smooth anesthesia. Grade III patients have a certain degree of risk in anesthesia and should be adequately prepared for anesthesia and take effective measures to actively prevent possible complications during anesthesia. Grade Ⅳ patients are extremely dangerous in anesthesia, and grade V patients are extremely critical and have very poor tolerance for anesthesia and may die at any time, so the anesthesia and surgery are exceptionally dangerous.