Postoperative bleeding
Postoperative bleeding can occur within 24 hours after surgery (called primary bleeding) and about 7-10 days after surgery (called secondary bleeding). Incomplete and imperfect intraoperative hemostasis, such as loosening of sutures ligating blood vessels; spasm of broken ends of small blood vessels and covering of blood clots, which temporarily stops bleeding from the trauma and causes some bleeding points to be missed, are the main causes of primary hemorrhage. Due to factors such as infection and extravasation of digestive fluids in the late surgical field, necrosis and rupture of some of the vessel walls can lead to secondary hemorrhage in the postoperative period.

Postoperative incision infection
It is related to lax aseptic technique or the patient's constitution and the nature of the lesion, plus fasting, malnutrition, combined anemia, diabetes mellitus, obesity fat liquefaction, and so on. Most of the incision infections occur 3~5 days after surgery, and the individual occurs later, after 3~4 weeks.

Incision splitting
Incision cracking mainly occurs in the abdomen and adjacent joints of the surgical incision. Most of the time of incision cracking is about 1-2 weeks after surgery, which is related to the following factors: (1) old and weak, malnutrition, chronic anemia, etc., poor healing of incision after surgery; (2) excessive local tension of the incision, hematoma and septic infection of the incision; (3) suture line is too thin, poorly sutured, and the peritoneum is torn during suture in the case of unsatisfactory anesthesia; (4) sudden coughing, straining to defecate and vomiting, and gastrointestinal flatulence after surgery.

Postoperative pain
Pain is an unpleasant sensation and emotional response caused by tissue damage or potential tissue damage. Pain is classified as acute or chronic based on the duration of the pain and the healing time of the injured tissue.

Acute postoperative gastric dilatation
Acute gastric dilatation can be induced by disturbances in water and electrolytes, large amounts of oxygen poured into the stomach during pressurized breathing under an anesthetic mask, persistent pyloric spasm after abdominal surgery, severe infections, and shock. After the onset of gastric wall tension is reduced, venous reflux is impaired, a large amount of body fluids and electrolytes into the stomach, so that the volume of the stomach increases rapidly and according to the rapid increase in gastric volume, the gastric cavity is enlarged.

Postoperative pulmonary atelectasis and pneumonia
Among the postoperative pulmonary complications, pulmonary atelectasis is the most common, and the causes are multiple. Patients who have been smoking for a long time are often accompanied by chronic bronchitis and have more secretions in the respiratory tract. The intraoperative and postoperative application of various painkillers and sedatives inhibits the expectorant function of the respiratory tract.

Postoperative deep vein thrombosis
Deep vein thrombosis (DVT): refers to the abnormal coagulation of blood in deep veins, which is a disorder of venous return. It occurs in the deep veins of the lower limbs, commonly after major orthopedic surgery, and can be divided into proximal and distal DVT, the former located in the popliteal vein or above, and the latter located below the popliteal vein. Proximal DVT is the main source of pulmonary embolism emboli.

Postoperative pulmonary embolism
Venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), has an annual incidence of 100-200/100,000 and is the third most common cardiovascular disease. Among them, acute pulmonary embolism is the most serious clinical manifestation of VTE and is a major factor in its morbidity, mortality and hospitalization.

Postoperative urinary retention
Urinary retention is a condition in which urine accumulates in the bladder and the patient is unable to expel it on his/her own. It is one of the common complications in surgical patients, causing greater pain to postoperative patients, and is also an important cause of postoperative urinary tract infection, which affects disease regression.

Postoperative abdominal infection
Vital system grading is the most important risk factor for postoperative abdominal infection, indicating that the patient's preoperative systemic condition is closely related to postoperative infection. Disease severity and age factors also reflect the patient's general condition and have an inter-factorial correlation with vital system classification.