In this study, we developed and validated a mobile terminal-based nomogram for predicting POF, major infection, and mortality using six independent prognostic factors (age, respiratory rate, albumin, lactate dehydrogenase, oxygenation, and pleural effusion) that readily available on admission. This nomogram was found to be superior with the both internal and external validation cohort compared with other prognostic scores recommended for clinical use for predicting POF and major infection. As POF is the diagnostic criteria for SAP, this nomogram is recommended for routine clinical use to predict SAP on admission or to rule it out (validation NLR 0.11/0.29). Therefore, these findings encourage the use of the simple-to-use web-based nomogram before new markers are developed and introduced in our settings. The consecutive nature of patient recruitment and short time from onset of pain to admission, stringently applied in two large different Chinese centers, adds strength to these conclusions.
Age is recognized as an individual risk factor for increased severity of AP and has been used by several prognostic scores [12, 13] and practice guidelines [49–51]. To investigate the role of age and comorbidity in the severity of AP, Frey et al. [52] carried out a retrospective study in 84,713 patients with a first-attack AP. They found that the 65 to 75 age group, and age > 75 are strong predictors of early death with an odds ratio (OR) of 2.6 and 5.2, respectively. Similar findings also applied to patients with two chronic comorbidities (OR: 3.5) or ≥ 3 comorbidities (OR: 7.4). Moreover, the mortality rate was only 0.1% (14/14,280) for younger patients (age < 55) without chronic comorbidities compared to 5.9% (701/24,852) for elderly patients (age > 64) with ≥ 3 comorbidities in the first 14 days. In addition, they showed that recent cancer, heart failure, and renal and liver diseases are strongly correlated with outcomes. Further, in acute interstitial AP, which is known to have low mortality, the Charlson comorbidity index was strongly associated with adverse clinical outcomes [53]. Because of the significant impact of the degree and number of comorbidities on clinical outcomes, we therefore excluded patients with advanced (end-stage) comorbidities with an emphasizing on assessing the intrinsic prognostic factors for AP severity.
Hypoalbuminemia occur in critically ill patients due to several factors including dilution from resuscitation, increased interstitial loss, altered liver function, and catabolic nutritional state [54]. It is strongly associated with poor clinical outcomes in acutely ill patients [55] and it has also been shown to independently associated with POF and mortality in AP patients [56, 57]. Whitcomb et al. [58] has recently found that albumin dropped rapidly in AP patients with multiple organ failure resulting in unregulated capillary leak with continued loss of larger plasma proteins. In contrast, the plasma albumin levels only dropped slightly in patients without multiple organ failure who tended to recover quickly unless they develop complications (infected pancreatic necrosis or sepsis). The therapeutic effect of albumin in inflammatory states is not only by affecting plasma volume dilation, but also by regulating inflammation and oxidative stress [59, 60]. Therefore, serum albumin level has been incorporated in some AP severity prognostic indices (Glasgow criteria [41] and nomogram [18]).
Raised lactate levels has been observed in many critical acute illness situations including sepsis [61] and AP [62–64]. Elevated lactate may serve as a protective mechanism and has been shown to reduce Toll-like receptor and inflammasome-mediated pancreatic and liver injury via its receptor GPR81 [65]. LDH can reversibly catalyze the oxidation of lactate to pyruvate and has been employed by Ranson, Glasgow, Japanese Severity Score [13], and a nomogram [17] for early AP severity prediction and reported as a simple and useful parameter for predicting POF [66, 67], and pancreatic necrosis [68]. Moreover, urinary LDH has also been reported as an useful biomarker for septic acute kidney injury [69].
Respiratory rate and oxygen support reflect respiratory status and with respiratory failure as one most common organ dysfunction in AP [9], the early recognition of respiratory dysfunction is considered important. Our results showed a positive association between the development of POF and an increased respiratory rate or requirement for oxygen support on admission. Therefore, both respiratory rate and oxygen support have been adopted in NEWS [38] for their convenience and prognostic value. The significance of pleural effusion in AP patients has been long reported [70], and is part of BISAP [40]. Our results showed that pleural effusion (odds ratio: 3.61 95%CI 1.97–6.6, P < 0.001) was an independent predictor for SAP, consistent with a previous study [71].
In our univariate analysis before establishing the predictive nomogram, we also found white blood cell count [13], glucose [13, 72], urea (or blood urea nitrogen) [6, 13], creatinine [13], and ionized calcium [13] were independent individual prognostic factors for POF, consistent with previously published literature. However, when these parameters were fitted into our multiple logistic regression model, they only had negligible impact on the final nomogram. Unlike most previously published studies included high proportion of SAP patients, we used a training consecutive cohort constituted only up to 10% of SAP patients which may partially explain different weights of individual prognostic factors in varied epidemiology situations. For example, three of the four existing predictive nomograms for AP severity were conducted in the ICU settings which cannot be generalizable for emergence departments or general wards where patients are primarily admitted.
Some of the six independent prognostic factors of our nomogram are included as part of NEWS (respiratory rate and oxygen support) and BISAP (age, respiratory rate, and pleural effusion), the two that we found had justifiable good predictive values for POF in both our training and internal validation cohorts. However, the nomogram was simpler than BISAP and more AP-specific than NEWS to quantitatively predict clinical outcomes in a personalized way. In addition, we validated the nomogram in another Chinese tertiary hospital with the etiological composition different from ours. The results showed that the nomogram with stable clinical applicability in both AP cohorts with hypertriglyceridemia (internal validation) or biliary (external validation) as the main etiology, adding strength to its applicability.
Our study also has some limitations. Firstly, the nomogram model was developed mainly based on the variables that were easy to get in our retrospective sets, but did not include other factors that may influence the precision of the model. For example, the oxygenation index was not included in our analysis because only paucity data were available. In a most recent study [73], the authors found that oxygenation index had low prognostic power (AUC 55.3%) for acute respiratory distress syndrome. Secondly, the nomogram did not have specific markers for circulatory and renal failure. The reasons for this may be attributed to low incidence of circulatory and renal failure of the study population and at the early disease stage respiratory failure commonly precedes other organ failures [5, 8]. Thirdly, the lack of international validation may limit the extrapolation and generalizability of the nomogram.