The Effect And Mechanism Research Of Abdominal Paracentesis Drainage For Severe Acute Pancreatitis Patients

BackgroundThe management of acute pancreatitis faced a substantial clinical aporia because of the process is ranged from self-limited without major physiologic insult,to intensive care and even surgery which accompanied with local and systemic complications and high mortality rate.At present,despite overall reduced mortality,the management of AP is still complicated because of the limited understanding of the pathogenesis of the disease.Nevertheless,it is generally accepted that,majority of AP patients who were diagnosed as severe acute pancreatitis(SAP)in the subsequent management,had(peri)pancreatic fat necrosis in the early stage of the disease.Actually,fat necrosis,which may occur after the onset of symptoms,is thought as an exacerbating factor correlated with the aggravation of the disease.Actually,it is considered as a part of the revised Atlanta criteria and several severity scoring systems such as Schroeder and Balthazar scoring system.In vitro studies,it is reported that free fatty acids(FFA),especially unsaturated fatty acids(UFA),is the main reaction product from the hydrolysis of adipocyte triglyceride which induced by the lipase released during pancreatitis.Moreover,we and others have previously found that metabolic abnormalities of serum FFA leads to distant organ injury and increasing systemic inflammatory,indicating the elevated serum FFA might participate in the process of fat necrosis worsening the pancreatitis.However,even fat necrosis and associated toxic factor-FFA's generation,are now largely accepted as causal roles of severity,few effective treatment is conducted in clinical management.Our previous research recommended a modified step-up approach in which a new procedure,abdominal paracentesis drainage(APD),was used during the early stage of treatment for severe acute pancreatitis(SAP).We found that patients with APD had a lower rate of mortality,less organ failure and lower inflammatory factors than the non-APD group in our retrospective clinical cohort study.Furthermore,we investigated the safety of APD using a prospectively study and confirmed that there was no increase in the rate of infections with the APD procedure.These previous studies suggest that APD could be beneficial in the treatment of patients with SAP and carries no additional risk of infection.However,the underlying mechanisms for APD's effectiveness are poorly understood.The possible mechanisms for the effectiveness of APD could come from two sources: 1)decreasing intra-abdominal hypertension(IAH);2)eliminating the toxic substances,mainly including inflammatory mediators,proteases and lipid metabolites in pancreatitis-associated ascitic fluid(PAAF).Among these substances,lipid metabolites,the reaction products of fat necrosis,have been demonstrated to be involved in the development and progression of pancreatitis.In addition,triglycerides(TG),which can be transformed into to FFA,have been reported to have a mild-to-moderate elevated level in plasma(2-10 mmol/L)in approximately half of the patients with AP.Similar to FFA,studies have shown that the serum TG elevation correlates with the aggravation of non-HTG-induced SAP.For example,we recently revealed that acute biliary pancreatitis(ABP)patients with TG elevation usually had higher risks of SAP and mortality,more organ failure and a greater likelihood of requiring further intervention compared with those with normal TG levels.These abovementioned studies indicate that lipid metabolites,especially TG and FFA,are enriched in PAAF and play a specific role in the progression of SAP.Although these advances in knowledge have been made,the exact roles of lipid metabolites in the effectiveness of APD have not been determined.Based on the previous studies and considering the high level of FFA found in pancreatitis-associated ascitic fluids(PAAF)which emerges in the majority of SAP patients,we hypothesized that: APD could eliminate the high level of FFA accumulated in abdominal cavity,and thus(i)inhibit its reabsorption to systemic circulation;(ii)reduce the fat necrosis and thus further prevent FFA's toxic effect on systemic inflammation and oxidative stress.These speculations promote us to investigate the underlying mechanism of APD in association with fat necrosis and its generation FFA during the pathogenesis of SAP.Methods1.A retrospective cohort of 132 consecutive non-HTG-induced SAP patients with TG elevation and pancreatitis-associated ascitic fluid(PAAF)was recruited from May 2010 to May 2015.Two groups were divided in the SAP patients: the APD group(n=68)and the non-APD group(n=64).The monitored parameters mainly included mortality,hospital stay,the incidence of further intervention,levels of serum lipid metabolites and inflammatory factors,parameters related to organ failure and infections,and severity scores.2.Under pentobarbital anesthesia,a total of 102 Sprague-Dawley rats were randomly divided into three groups as 1)the sham group(n=34): in which the rats only underwent sham surgery;2)the SAP group(n=34): according to our previously experience,SAP rat with PAAF was induced via a retrograde infusion of 5% sodium taurocholate(1 ml/kg body weight)into the biliopancreatic duct over one minute;and 3)the SAP+APD group(n=34): in which a type of modified surgical drainage tube was used after injection of sodium taurocholate.For this drainage,one end of the drainage tube was inserted into the right lower quadrante before the abdomen was closed,and the other end was connected with a negative-pressure ball device.Six rats per group were anesthetized as previously mentioned and sacrificed at each time point(8,16,24,and 32 h after the infusion of taurocholate).In this part there had 10 animals in each group for mortality study,and the mortality was recorded every 4 hours and up to 32 hours after the procedure.3.A total of 48 Sprague-Dawley rats were divided into 3 groups as 1)the MAP group(n=16): Caerulein pancreatitis was induced in rats with two doses of 20 ug/kg of caerulein administered intraperitoneally,for three consecutive days as described by Singh and his colleagues;2)the MAP+OA group(n=16): a single dose of 1200?mol/L OA was given intraperitoneally 2h after the first dose of caerulein.The administered volume and dose are based on the mean volume of PAAF and the mean concentrations of OA in PAAF observed in 24 h in taurocholate-induced SAP rats.3)the sham group(n=16): which were given 8mL 0.9% PBS intraperitoneally instead of OA at 2h after the first Caerulein injection.Rats were anesthetized as previously mentioned and sacrificed 24 h after the last caerulein injection.Studies for this part had a total of 24 for 24h-mortality studies.Results1.The demographic data and severity scores were comparable between the two groups.Compared with the non-APD group,the primary outcomes(including mortality,hospital stay and the PCD incidence of percutaneous catheter drainage)in the APD group were improved.The serum levels of lipid metabolites were significantly lower in the APD group after 2 weeks of treatment than in the non-APD group.Logistic regression analysis indicated that the decreased extent of free fatty acid(FFA)(odds ratio,1.435;P = 0.015)was a predictor of clinical improvement after 2 weeks of treatment.2.The cumulative mortality rate at 32 hours in the SAP group after operation was 70%(7/10),which was significantly higher in comparison to 30%(3/10)in the SAP+APD group(P<0.05);In parallel,it was observed that the SAP+APD group received significant lower score than the SAP group at 24 and 32 h post-induction(24h: 15.4±4.5 vs.9.1±3.2,P<0.05;32h: 17.3±4.8 vs.9.5±3.0,P<0.001).Furthermore,the number of fat necrosis dots detected in the SAP+APD group after 24 hours of induction was significantly less than that in the SAP group.In addition,a dramatically increase of cytokines((TNF-a: 36.2±15.1 vs.23.5±7.4 pg/m L,P<0.05;IL-1?: 24.5±8.7 vs.15.2±7.2 pg/mL,P<0.05,respectively)and serum TBARS(26.5±5.4 vs.12.8±3.8 nmol/L,P<0.05)were found in the SAP group after 32 h,which were prevented in the SAP+APD group.3.All of the rats in the MAP group and sham group survived in 24 h after induction,in contrast rats coadministered OA had 50% mortality.Furthermore,the serum TNF-a,IL-1? and TBARS had significant higher increased tendency in the MAP+OA group compared to the MAP group(TNF-a: 26.0±12.5 vs.11.9±4.6 pg/m L,P<0.05;IL-1?: 18.3±5.8 vs.6.5±2.9 pg/m L,P<0.05;TBARS: 0.68±0.15 vs.2.03± 0.84 nmol/mg,P<0.05,respectively).More importantly,at the time of necropsy,no visceral fat necrosis was detected in the MAP group.In contrast,the MAP+OA group showed a comparative severe fat necrosis.Conclusion1.APD is beneficial for non-HTG-induced SAP patients with elevated TG and PAAF.Notably,a novel mechanism was revealed through which the reduction of serum TG and FFA may account for the beneficial effect.2.APD could ameliorate the pathogenesis of SAP and finally decrease the mortality.In addition to prevent the high level of serum FFA,APD could also relieve the abdominal fat necrosis,as well as improving the systemic inflammation and oxidation stress.3.Intra-peritoneal administered OA could aggravate the pathogenesis of MAP,the underlying mechanism might be the furtherance of fat necrosis and finally amplifying the inflammation and oxidation accompanied with pancreatitis.