ASA classification is generally divided into six grades: ASA1 is a healthy patient who can tolerate surgical anesthesia; ASA2 is a patient with mild systemic disease with no functional impairment who can tolerate surgical anesthesia; AS3 is a patient with severe systemic disease with some functional impairment who can still tolerate anesthesia; ASA4 is a patient with severe systemic disease and a lifelong need for uninterrupted treatment with extreme anesthetic risk requiring adequate and meticulous preanesthetic preparation; ASA5 is a dying patient who is unlikely to survive within 24 hours regardless of surgery; ASA6 is a brain-dead patient.