The course of severe acute pancreatitis has a certain regularity. The whole course of the disease can be roughly divided into 3 phases. 1, the acute reaction period: from the onset to about 2 weeks, characterized by a systemic inflammatory response, often accompanied by shock, acute respiratory distress syndrome (ARDS), acute renal failure and pancreatic encephalopathy and other major complications. In addition to abdominal pain and distension, patients in this period also have impairment of other organ functions throughout the body. Patients may present with fever, shortness of breath, dyspnea, rapid heart rate, decreased blood pressure or even shock, oliguria or even anuria, gastrointestinal bleeding, irritability, babbling or even coma, etc. Treatment in this stage is usually carried out in the ICU with close monitoring and strong organ function support, and some patients need tracheal intubation (incision) with ventilator-assisted breathing, or the need for blood purification therapy, and a few patients need emergency surgery. Due to the development of the disease process itself, the patient’s condition can still gradually worsen after admission, and even multi-organ failure, some patients may die at this stage, the first peak of death in severe acute pancreatitis. 2, the systemic infection period: patients through the acute phase, the systemic condition gradually improved, there will be a short period of “stable condition”. However, at this time, it cannot be considered that pancreatitis has been cured. At this time, patients have more or less local complications in the peripancreatic area, such as peripancreatic fluid, necrotic infection, peripancreatic abscess and bleeding. In some patients, local complications do not require special treatment and can be cured by self-absorption under close observation; in some patients, they can be cured by puncture and drainage; in some patients, complications such as infection, abscess, bleeding, intestinal fistula, etc. need to be treated by caesarean operation. Due to the specificity of pancreatitis, postoperative continuous flushing and drainage is usually required for several months (or even longer), some patients can develop complications such as hemorrhage, abscess, intestinal fistula, sometimes requiring multiple surgical treatments, and a few patients can develop fungal infections, multi-organ failure, and even death, which is the second peak of death in severe acute pancreatitis. 3, residual infection period: The time is several months later, mainly manifested as general malnutrition, the presence of retroperitoneal or intra-abdominal residual pus cavity.