Abstract： Objective To describe the clinical characteristics of critical acute pancreatitis (CAP) and the predictive value of intra abdominal pressure and APACHE Ⅱ score in this group of patients.Methods From January 2010 to March 2013,acute pancreatitis patients between 18 to 75 years old present to the SICU,Department of General Surgery,General Hospital of Nanjing Military Area Command within 96 hours of symptoms onset were screened and forty-seven patients who met the diagnostic criteria of critical acute pancreatitis according to the determinant-based classifications were included in this study.The APACHE Ⅱ score was calculated within 24 h of admission,intra abdominal pressure was measured.Moreover,occurrence of organ dysfunction,need of surgical intervention,length of ICU and hospital stay was also recorded.Receiver operating characteristic curve was used to evaluate predictive accuracy of intra abdominal pressure and APACHE Ⅱ score for mortality and need of surgery.In addition,the correlation between intra abdominal pressure,APACHE Ⅱ score and length of hospital and ICU stay were also analyzed.Results Among the 47 study patients,the median APACHE Ⅱ score and intra abdominal pressure were 13 and 16.9 mmHg,respectively.Positive blood culture was detected in 22 patients.Respiratory dysfunction occurred in 45 cases (96％),while renal dysfunction occurred in 34 patients (72％) and cardiovascular dysfunction in 22 (47％).Double organ dysfunction and triple organ dysfunction happened in 16 and 19 patients,respectively.Seventeen (36％) patients needed surgical intervention.The mortality of critical acute pancreatitis patients was as high as 38％ (18/47).The median length of ICU and hospital stay was 31 and 38 days,respectively.Both APACHE n score and intra abdominal pressure increased significantly as the number of organ dysfunction increased,the difference was statistically significant (P ＜0.001).For the prediction of mortality,intra abdominal pressure performed better than APACHE Ⅱ score with an area under curve of 0.80 (95％ CI 0.41-0.76) compared with 0.58 (95％ CI0.38-0.73).Taking 16.1 mmHg as the cut-off value,the sensitivity and specificity of intra abdominal pressure in predicting mortality were 83％ and 62％,respectively compared with 44％ and 73％,respectively for APACHE Ⅱ score (13.5 as the threshold).However,both of the parameters had limited accuracy in the prediction of needs for operation and no correlation was found between the two parameters and the length of ICU and hospital stay.Conclusions Critical acute pancreatitis is an extremely severe type of acute pancreatitis with very high mortality and rate of surgical intervention.Early intra abdominal pressure measurement can well predict the poor prognosis of this entity.