ObjectiveTo observe the clinical characteristics, the characteristics of organ dysfunction and death related factors in the natural course of severe acute pancreatitis (SAP). MethodsThe data of 302 cases of SAP from January 1999 to June 2007 in our hospital were retrospective analyzed. The APACHEⅡscore, state of each organ, and death related factors were recorded and analyzed according to the admission and on 1, 3, 5, 7, 14, and 28 d after admission, a total of 7 time points. ResultsIn natural course of SAP, the APACHEⅡscore took on a double-peak type distribution, the peaks appearing nearly about one week and two weeks after the onset of SAP. Systemic inflammatory response syndrome (SIRS), hypoxemia, metabolic acidosis, hyperglycemia, and abdominal compartment syndrome were the main causes of early organ failure. Incidence of organ failure and infection increased significantly for patients with intestinal paralysis lasting longer than five days. The most affected organ failure was followed by respiratory organs, peripheral circulation, kidneys, and gastrointestinal tract. The mortality rate increased significantly for patients with organ failure more than 48 hours. Four cases of death (9.5%) caused by severe shock and cardiac arrest within 24 h after admission; 6 deaths (14.3%) led by persistent shock with ARDS or acute renal failure within 24-72 h; 14 cases of death (33.3%) arose from 3-10 d after onset, mainly for acute respiratory distress syndrome (ARDS), acute renal failure associated with multiple organ dysfunction syndrome (MODS); 18 cases (42.8%) of the death arose on 10 d after the onset, mainly for the MODS caused by intra-abdominal infections, bleeding, pancreatic fistula, and biliary fistula. ConclusionsThe natural course of SAP can be divided into three phases:systemic inflammation, systemic infection, and recovery. Duration of intestinal paralysis is an important factor affecting the natural history of SAP. Early complications in patients with organ failure appeared as SIRS, metabolic acidosis, hyperglycemia, and abdominal hypertension. MODS led by SIRS is the leading cause in early death of SAP; MODS caused by pancreas and peripancreatic tissue infections, abdominal bleeding, pancreatic fistula, and biliary fistula are the main death factor in the late phase. Early recovery of gastrointestinal function can reduce the incidence of MODS.