Severe acute pancreatitis (SAP) is the most severe form of acute pancreatitis (AP) and Infection of pancreatic necrosis (IPN) have shown to be one of the decisive factors defining the severity of illness.

Minimally invasive techniques including endoscopy, laparoscopy, retroperitoneal approaches, etc., have recently been widely used for debridement because the procedure can further reduces surgical stress and performed not require general anesthesia, thereby reducing complications. Studies have shown that endoscopic transgastric necrosectomy can significantly reduced the proinflammatory response, complications, and hospital stay. Despite these advantages, there are some limitations with this approach. First, transgastric necrosectomy should be performed as late (about 4 weeks) in the course of the disease as possible to allow necrosis to wrap, since early debridement may result in a higher patient fatality rate. However, patients with SAP are often in a severely ill state due to sepsis or MODS at an early stage, which causes them unable to adhere to necrotic tissue encapsulation by conservative treatment. Second, the ideal patient to select for this approach has necrosis confined in the vicinity of gastroduodenal location. Last, up to 27% of IPN patients require additional percutaneous catheter drainage (PCD) after undergoing endoscopic transluminal therapy. This may be explained by the fact that dissemination of necrosis, digestive enzymes and inflammatory mediators from the necrotic tissue lumen to other parts of the abdominal cavity during endoscopic procedures.

Percutaneous catheter drainage (PCD) has always been the principal treatment measure for patients with AP at early stage (< 4 weeks) or those with collections or necrosis extending into deeper anatomical planes. Irrigation through peripancreatic drainage placed after open laparotomy has been the standard treatment for patients with AP who had undergone surgical necrosectomy. However, this proactive approach has not been widely used in the setting of PCD.

To adequate drainage and removal of necrosis, an early percutaneous continuous irrigation assisted vacuum drainage in combination with subsequent endoscopic transgastric necrosectomy which has not been reported so far was applied in critically ill patients with SAP.

Severe Acute Pancreatitis (SAP) Treatment Protocol After admission, patients were given intravenous analgetics, omeprazole and somatostatin, and nasojejunal tubes were placed for EN. Once fever developed, broad-spectrum antibiotics were given empirically. If the patient was concomitant with shock, respiratory failure, and acute kidney injury, appropriate organ support was provided. Patients with biliary pancreatitis was given encoscopic retrograde cholangiopancreato graphy (ERCP) within 24 h after admission. When the patient was diagnosed with hyperlipidemic pancreatitis and plasma triglyceride ≥11.3 mmol/L, plasma exchange was administered immediately. All patients were given contrast enhanced CT within 48 hours after admission to identify the location and range of the necrosis and calculate the CT severity index (CISI).

Procedure All PCD and endoscopic procedures were performed under conscious sedation or local anesthesia. If the patient's condition progressively worsened, a multifunctional irrigation-assisted vacuum drainage tube was placed by the CT-guided Seldinger technique in each of the necrosis cavity. The tube was administered with continuous internal irrigation and vacuum drainage as described in below: (1) the end of the drainage tube (the adapter) was connected to a vacuum device that delivers a controlled negative pressure within the range of 8-10 kPa. (2) a large volume of 0.9% normal saline was infused into the necrosis cavity constantly (1500mL a day, 65mL an hour) through the durg entrance, allowing for continuous irrigation; (3) the inside drainage tube was flush by rapid manual injection of 50-100 mL 0.9% normal saline twice a day through the drug entrance and inject 20-50 mL of 0.9% normal saline daily through water entrance to prevent the tube from becoming blocked by necrosis, debris or omentum; (4) total irrigation and drainage volume were checked every 8 hours to keep the irrigation-drainage balanced. All tubes were checked daily and replaced when the tube was translocated or blocked. When the volume of irrigation exceeds the drainage 500 mL/day or if there were serious complications associated with the drainage tube, continuous irrigation and vacuum drainage should be stopped immediately and the tube was the traditional drainage was performed.

Approximately 4 weeks after disease onset or the formation of well-defined wall was confirmed by repeat CT scan, transgastric necrosectomy were performed by one or two experienced endoscopist under conscious sedation. Transgastric necrosectomy was repeated, mostly every three to five days, until all loosely adherent necrotic material were cleared and replaced by granulation tissue. In the course of the procedure, antibiotic administration was adjusted based on the results of the microbiological culture results. Subsequently, percutaneous irrigation was stopped and replace with simple drainage if the patient's condition continues to improved and the cavity confirmed by CT was resolution. If the drainage volume was less than 10 mL/day for 3 consecutive days, clamp the drainage tube and remove it finally.

Inclusion Criteria:

• Diagnosed with SAP
• Concurrent IPN

Exclusion Criteria:

• Age <18 years or > 80 years
• Patients or family members disagreed with this study

patients with SAP and IPN;SAP was diagnosed according to the revised Atlanta classification, which defined simultaneous persistent single or multiple organ failure >48h;IPN was considered when the following situations occur: persistent fever ≥38.5℃; increasing blood white blood cells (WBC), C-reactive protein (CRP) or procalcitonin; rapid deterioration of clinical deterioration; signs of gas was present in areas of necrosis. IPN is confirmed when the patient undergoes fine needle aspiration and the culture was positive.