Sepsis is one of the most common causes of death in critically ill patients. At present, there are only a few studies focused on postoperative sepsis. This study focuses on sepsis after operation of gastrointestinal tumor. In this study, the mortality rate is lower than that of sepsis reported in the literature , which may be related to the fact that most of the infection sources of the patients we selected are abdominal infection and we can actively control the infection sources by multidisciplinary cooperation. In this study, 181 patients with sepsis who were admitted to ICU after operation of gastrointestinal tumor were analyzed retrospectively and we found that BMI༞20 kg/m2, lactic acid༞3 mmol/L after entering ICU and APACHE II score༞20 within 24 h after entering ICU were independent prognostic factors.
The World Health Organization classified BMI: BMI༜18.5 kg/m2 was underweight, 18.5 ≤ BMI༜25 kg/m2 was normal weight, 25 ≤ BMI༜30 kg/m2 was overweight and BMI ≥ 30 kg/m2 was obesity . In this study, we found that patients with BMI༞20 kg/m2 had a better prognosis than those with BMI ≤ 20 kg/m2, so we guessed that BMI༞20 kg/m2 might be a protective factor. However, the number of patients in this study was limited, and we did not conduct a more detailed stratified study. There were many reports about the relationship between BMI and the prognosis of sepsis, though the results were still controversial [14, 15]. Matthaios PO et al.  found that the mortality of obese patients with sepsis increased significantly. But one recent meta-analysis divided sepsis patients into three groups: overweight (25༜BMI ≤ 30 kg/m2), obesity (30༜BMI ≤ 40 kg/m2) and morbid obesity (BMI༞40 kg/m2). The results showed that the death risk of overweight patients with sepsis was reduced, while obesity and morbid obesity patients with sepsis did not increase the death risk. The reason for this controversy might be related to the distribution of adipose tissue. It was reported that the visceral fat (VAT) accumulation detected by CT scan was a risk factor for poor prognosis of sepsis. Sepsis patients with a high ratio of VAT area to subcutaneous fat (SAT) area had an increased risk of death and organ damage . In future, more detailed and rigorous studies should be designed to clarify the relationship between sepsis and BMI.
Lactic acid was constantly produced in metabolism and exercise, but its concentration generally did not rise. Only when the production of lactic acid was accelerated and lactate could not be removed in time, its concentration would increase. Generally speaking, when the energy of the tissue could not be satisfied by aerobic respiration, the tissue could not get enough oxygen or could not deal with oxygen fast enough, the concentration of lactic acid would rise. Hence, sepsis and septic shock guidelines used lactic acid as an indicator of tissue hypoperfusion and as a target for fluid resuscitation [5, 6]. Many studies had shown that lactate was an independent risk factor for sepsis prognosis [18–20]. In our study, it was also confirmed that the lactic acid༞3 mmol/L after entering ICU was an independent risk factor for sepsis patients after the gastrointestinal tumor surgery.
There were many scoring systems for evaluating the severity of critical patients, such as SOFA score and APACHE II score [21–23]. APACHE II score had been considered as the gold standard for risk assessment of critical patients in the past. Several studies had confirmed that APACHE II score is an independent risk factor for the prognosis of sepsis patients [24, 25]. In our study, we found that the SOFA score and APACHE II score within 24 hours after entering ICU were statistically significant in the univariate analysis, while the multivariate analysis showed that only APACHE II score༞20 was an independent risk factor in this group. However, there was evidence that APACHE II score might provide inaccurate information in some patients, for example, in patients with unconsciousness, the score might be too high . Therefore, we need to increase the sample size to confirm this result in future.
The limitations of this study should be referred. First, this study was a retrospective study and the subjects of this study were patients with sepsis who were admitted to ICU after operation of gastrointestinal tumor, so, whether the results could be extended to all sepsis populations remains to be confirmed. Second, patients with sepsis in the general ward were not included in this study, and most of these patients improved in our hospital. Therefore, the mortality of patients with sepsis after gastrointestinal surgery might be overestimated in our study. In the future, we will design prospective research to verify it. Third, there were several missing data, especially BNP, echocardiography etc. So we could not accurately evaluate their impact on the prognosis of sepsis patients. Finally, the small sample size of this study increased the risk of type two error which made the study power limited. We hope that there will be more large-scale researches to confirm these results in the future.