Retrospective Cohort Study Open Access
Copyright ©The Author(s) 2024. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. May 28, 2024; 30(20): 2657-2676
Published online May 28, 2024. doi: 10.3748/wjg.v30.i20.2657
Development and validation of a new prognostic model for patients with acute-on-chronic liver failure in intensive care unit
Zong-Yi Zhu, Xiu-Hong Huang, Hui-Qing Jiang, Li Liu, Department of Gastroenterology, The Second Hospital of Hebei Medical University, Shijiazhuang 050000, Hebei Province, China
Zong-Yi Zhu, Department of Gastroenterology, Weixian People's Hospital, Xingtai 054700, Hebei Province, China
ORCID number: Hui-Qing Jiang (0000-0001-8706-0943); Li Liu (0000-0003-0597-9222).
Co-corresponding authors: Hui-Qing Jiang and Li Liu.
Author contributions: Zhu ZY analyzed the data and wrote the paper; Huang XH collected the data; Jiang HQ and Liu L designed the study and revised the paper; all authors have read and approved the final version. Jiang HQ and Liu L contributed equally to this work as co-corresponding authors. There are two reasons for designating Jiang HQ and Liu L as co-corresponding authors. First, this study was performed as a collaborative effort, and the designation of co-corresponding authorship accurately reflects the distribution of responsibilities and burdens associated with the time and effort required to complete the study and the resultant paper. This also ensures effective communication and handling of post-submission matters, ultimately enhancing the paper's quality and reliability. Second, Jiang HQ and Liu L contributed efforts of equal substance throughout the study process. The choice of these two researchers as co-corresponding authors acknowledges and respects this equal contribution, while recognizing the spirit of teamwork and collaboration of this study. In summary, we believe that designating Jiang HQ and Liu L as co-corresponding authors is fitting for our manuscript as it accurately reflects our team's collaborative spirit, equal contributions, and diversity.
Institutional review board statement: MIMIC-Ⅳ and EICU are public databases in which all patients' private information is anonymous. Therefore, the approval for use of MIMIC-Ⅳ and EICU databases by local ethics committee was waived. This study was reviewed and approved by the SHHMU Institutional Review Board (Approval number: 2024-R230).
Informed consent statement: Informed consent from patients in the MIMIC-IV and EICU cohorts was obtained during the original data collection. Informed consent from patients in the SHHMU cohort was waived due to retrospective nature of this study.
Conflict-of-interest statement: The author declares that there is no conflict-of-interest.
Data sharing statement: No additional data are available.
STROBE statement: The authors have read the STROBE Statement—checklist of items, and the manuscript was prepared and revised according to the STROBE Statement—checklist of items.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Li Liu, MD, Chief Physician, Department of Gastroenterology, The Second Hospital of Hebei Medical University, No. 215 West Road, Shijiazhuang 050000, Hebei Province, China. loraliu@163.com
Received: January 13, 2024
Revised: April 22, 2024
Accepted: May 9, 2024
Published online: May 28, 2024
Processing time: 133 Days and 2.6 Hours

Abstract
BACKGROUND

Cirrhotic patients with acute-on-chronic liver failure (ACLF) in the intensive care unit (ICU) have a poor but variable prognoses. Accurate prognosis evaluation can guide the rational management of patients with ACLF. However, existing prognostic scores for ACLF in the ICU environment lack sufficient accuracy.

AIM

To develop a new prognostic model for patients with ACLF in ICU.

METHODS

Data from 938 ACLF patients in the Medical Information Mart for Intensive Care (MIMIC) database were used to develop a new prognostic model (MIMIC ACLF) for ACLF. Discrimination, calibration and clinical utility of MIMIC ACLF were assessed by area under receiver operating characteristic curve (AUROC), calibration curve and decision curve analysis (DCA), respectively. MIMIC ACLF was then externally validated in a multiple-center cohort, the Electronic Intensive Care Collaborative Research Database and a single-center cohort from the Second Hospital of Hebei Medical University in China.

RESULTS

The MIMIC ACLF score was determined using nine variables: ln (age) × 2.2 + ln (white blood cell count) × 0.22 - ln (mean arterial pressure) × 2.7 + respiratory failure × 0.6 + renal failure × 0.51 + cerebral failure × 0.31 + ln (total bilirubin) × 0.44 + ln (internationalized normal ratio) × 0.59 + ln (serum potassium) × 0.59. In MIMIC cohort, the AUROC (0.81/0.79) for MIMIC ACLF for 28/90-day ACLF mortality were significantly greater than those of Chronic Liver Failure Consortium ACLF (0.76/0.74), Model for End-stage Liver Disease (MELD; 0.73/0.71) and MELD-Na (0.72/0.70) (all P < 0.001). The consistency between actual and predicted 28/90-day survival rates of patients according to MIMIC ACLF score was excellent and superior to that of existing scores. The net benefit of MIMIC ACLF was greater than that achieved using existing scores within the 50% threshold probability. The superior predictive accuracy and clinical utility of MIMIC ACLF were validated in the external cohorts.

CONCLUSION

We developed and validated a new prognostic model with satisfactory accuracy for cirrhotic patients with ACLF hospitalized in the ICU. The model-based risk stratification and online calculator might facilitate the rational management of patients with ACLF.

Key Words: Acute-on-chronic liver failure, Cirrhosis, Risk stratification, Prognosis, Model, Scores

Core Tip: Patients with acute-on-chronic liver failure (ACLF) usually need to be hospitalized in intensive care unit for condition monitoring and organ support therapy where existing prognostic scores for ACLF have a limited predictive accuracy. In this study, we developed a new prognostic model [Medical Information Mart for Intensive Care (MIMIC) ACLF] using data in MIMIC database for patients with ACLF. MIMIC ACLF not only exhibited a satisfactory predictive accuracy and clinical utility in MIMIC cohort, but also performed well in external single and multiple-center validation cohorts. In addition, we performed a risk stratification and developed an online calculator based on MIMIC ACLF to facilitate its application in clinical practice.



INTRODUCTION

Liver cirrhosis is the common end stage of all chronic liver diseases. Acute decompensation (AD) and its final and most fatal stage, acute-on-chronic liver failure (ACLF), are major causes of death in patients with liver cirrhosis[1]. ACLF was first defined by European Association for the Study of Liver-Chronic Liver Failure (EASL-CLIF) Consortium as a distinct syndrome characterized by AD of cirrhosis, precipitating events, systemic inflammatory response, multiple organ failures and high short-term mortality[2]. Despite the progress in understanding of the pathophysiological mechanisms of ACLF, including intense systemic inflammatory response, immune dysfunction, metabolic changes, oxidative stress and mitochondrial dysfunction[3,4], no specific or definitive treatment is available for ACLF except for liver transplantation (LT)[5]. The main principle in management of ACLF is to treat precipitating events and associated complications and provide organ support therapy[6,7].

To monitor the disease condition and receive organ support therapy, patients with ACLF usually need to be transferred to the intensive care unit (ICU). In the ICU, reasonable management of ACLF should be consistent with the patient's prognosis. For patients with a relatively optimistic prognosis, ongoing aggressive therapy should be provided without hesitation as a bridge to LT; while for those with poor prognosis, considering their economic burden and limited medical resources, palliative therapy might be an optimal choice. Therefore, an excellent prognostic score that can accurately predict the prognosis of patients with ACLF is very important for decision-making by clinicians in the ICU. At present, existing prognostic scores for patients with ACLF in the ICU mainly include Child-Turcotte-Pugh (CTP), Model for End-stage Liver Disease (MELD), MELD-Na and Chronic Liver Failure Consortium (CLIF-C) ACLF (CLIF-C ACLF). Developed for cirrhotic patients, CTP, MELD and MELD-Na are traditional prognostic scores that do not consider the importance of multiple organ failure[8], resulting in a limited accuracy[9-11]. Compared with traditional scores, CLIF-C ACLF is a recently (2014) developed prognostic score by the EASL-CLIF Consortium[12], showing significantly superior prediction performance for 28/90 d mortality in ACLF patients to the traditional scores[12-14]. However, some later studies found that the prediction performance of CLIF-C ACLF was not so ideal[15-17] (concordance index < 0.8), especially in the ICU. In addition, CLIF-C ACLF was not fully developed for ACLF patients hospitalized in ICU and has several limitations, such as ceiling effect of serum bilirubin, international normalized ratio (INR) and creatinine, difficulty in differentiating hepatic encephalopathy (HE) grade 1 from grade 0; and subjective variability in determining use of vasopressors[18], which might reduce its predictive accuracy.

In this study, we aimed to develop a new prognostic model for cirrhotic patients complicated with ACLF in ICU using data from Medical Information Mart for Intensive Care (MIMIC) database and externally validate it in the multiple-center intensive care cohort, the electronic ICU (eICU) collaborative research database and a Chinese single-center general ward cohort from the Second Hospital of Hebei Medical University (SHHMU) in China. We hope that this new prognostic model has satisfactory accuracy and is convenient for predicting short-term mortality in cirrhotic patients with ACLF.

MATERIALS AND METHODS
Patients

Patients included in this retrospective cohort study were from the MIMIC-Ⅳ database, the eICU database and the SHHMU cohort. MIMIC-Ⅳ is a large and freely available database that comprises anonymous medical records of patients admitted to the ICUs of Beth Israel Deaconess Medical Center between 2008 and 2019[19,20]. The eICU is a large, multi-center intensive care database jointly developed by the Philips Medical and Computational Physiology Laboratory of Massachusetts Institute of Technology on the basis of success of MIMIC database[21]. This database contains medical data of more than 200000 patients who were admitted to the ICUs at 208 hospitals in the mainland United States from 2014 to 2015. Because the source hospital of MIMIC database, Beth Israel Deacon Medical Center, is not involved in the eICU program, the eICU database is completely independent of the MIMIC database. The SHHMU cohort included cirrhotic patients with ACLF hospitalized in the Gastroenterology department at SHHMU. The MIMIC cohort was used for development and internal validation of a new prognostic model (MIMIC ACLF). The eICU and SHHMU cohorts were used for external validation of MIMIC ACLF in the environment of ICU and general ward, respectively. The reason we selected the SHHMU cohort is that although most ACLF patients require hospitalization in the ICU, there are still a few patients receiving treatment in the general ward. The inclusion criterion was cirrhotic patients with ACLF hospitalized for various ADs (ascites, bacterial infections, acute variceal bleeding and HE). The exclusion criteria were as follows: (1) < 18 years of age; (2) pregnancy; (3) incomplete records; (4) hepatocellular carcinoma (HCC) or malignant tumors from other organs; (5) human immunodeficiency virus (HIV) infection or undergoing immunosuppressive therapy; (6) death within 24 h of ICU admission; and (7) loss of follow-up.

Data collection

Data in MIMIC-Ⅳ (version: 2.0) and EICU (Version: 2.0.1) databases, including age, gender, race, category of AD, first day vital signs, first day laboratory parameters, vasopressors therapy, mechanical ventilation therapy, renal replacement treatment therapy, severity scores, and survival information were extracted through Postgres Structured Query Language (PostgreSQL) programming in Navicat Premium software. For those admitted multiple times to the ICU, data from their first admission were used. For laboratory tests that were measured more than one time, maximum or minimum values were selected according to the clinical implications, such as the maximum of total bilirubin (TB) or minimum of albumin. Patient’s data in the SHHMU cohort was obtained through electronic medical record system.

Scoring calculation formula

For the MIMIC and eICU cohorts, MELD and APACHE II scores were obtained directly from the MIMIC and eICU databases, respectively. For the SHHMU cohort, MELD was calculated as: 3.8 × ln [bilirubin (mg/dL)] + 11.2 × ln (INR) + 9.6 × ln [creatinine (mg/dL)] + 6.4 × (cirrhosis etiology: Biliary or alcoholic 0, others 1)[22]. The MELD-Na score was calculated as: MELD + 1.59 (135-Na) with maximum and minimum Na of 135 and 120 mEq/L, respectively[23]. The CLIF-C ACLF score were calculated as: 10 × {0.33 × CLIF- organ failures (OFs) + 0.04 × age + 0.63 × ln [white blood cell (WBC) count] – 2}[12].

ACLF diagnostic criteria

ACLF was defined by EASL-CLIF consortium[2] and diagnosed/graded according to CLIF-OF score[12]. Specifically, liver failure was defined as TB ≥ 12 mg/dL; coagulation failure was defined as INR ≥ 2.5; renal failure was defined as creatinine > 2 mg/dL or requirement of renal replacement therapy; circulatory failure was defined as requirement of vasopressor therapy to maintain blood pressure; cerebral failure was defined as HE grade III or IV (West Haven criterion); respiratory failure was defined as PaO2/FiO2 ≤ 200 or SpO2/FiO2 ≤ 214 or mechanical ventilation for reasons other than airway protection in cerebral failure[12]. ACLF grade 1 was defined as: (1) Single renal failure; (2) single failure of liver, coagulation, circulation or respiration along with a serum creatinine ranging from 1.5 to 1.9 mg/dL and/or mild to moderate HE; and (3) single cerebral failure along with serum creatinine ranging from 1.5 and 1.9 mg/dL. ACLF grade 2 and grade3 were defined as: 2 and ≥ 3 OFs, respectively[12].

Study outcomes

The outcomes of this study were 28-day and 90-day all-cause mortality. MIMIC-IV database contains patient survival information, both within or outside the hospital. The eICU database contains patient in-hospital survival information. For the SHHMU cohort, survival information was obtained from electronic medical records system or by contacting patients’ relatives through reserved phone numbers. Follow-up started on the date of patient admission and ended at 28 days and 90 days after admission or upon patient death.

Statistical analyses

Continuous variables with a normal or skewed distribution are described as the means ± SD and medians (interquartile range), respectively. Categorical variables are described as numbers (percentages). Univariate and multivariate proportional hazards regression analyses considering LT as the competing risk were performed to identify the independent variables for 28-day mortality[12,24]. Variables with P values < 0.05 in the univariate analysis were transformed to their natural logarithms and considered for multivariable analysis. To evaluate the performance of prognostic scores in predicting mortality, discrimination, calibration and overall performance of each score were evaluated. Discrimination were evaluated by plotting receiver operating characteristic (ROC) curve and calculating the area under curve (AUC). Bootstraps with 1000 resamples were applied to correct the AUC and explain the variance due to overoptimism. Calibration was evaluated according to the P value in Hosmer-Lemeshow “goodness-of-fit” test and the visually observed concordance between predicted and actual survival proportions in calibration curves. Overall performance was assessed using the Brier score and R2 value. A lower Brier score or higher R2 value indicates a superior performance[25]. Clinical utility was determined by determining the net benefit in decision curve analysis (DCA)[26]. Cumulative survival curves were plotted using the Kaplan-Meier method and overall survival proportion were compared by log-rank test. Statistical analysis was performed using MedCalc statistical software version 19.0.4, STATA 15.0 and R version 4.2.0. A two-tailed P value < 0 .05 was considered to be statistically significant.

RESULTS
Baseline characteristics

In the MIMIC cohort, 3256 consecutive cirrhotic patients with various forms of ADs were screened and 2005 patients were excluded for the following reasons: Lack of ACLF diagnosis (n = 900), incomplete records (n = 903), HCC or malignant tumors from other organs (n = 40), HIV infection or undergoing immunosuppressive therapy (n = 68) and death within 24 h of ICU admission (n = 94). Finally, 1251 cirrhotic patients complicated with ACLF were enrolled in this study. These patients were then randomly divided into a derivation cohort (n = 938) and an internal validation cohort (n = 313) at a ration of 3:1. In the eICU cohort, 1042 cirrhosis patients admitted due to various ADs were screened and 491 patients were excluded, resulting in a total of 551 cirrhotic patients with ACLF participating in the study. In the SHHMU cohort, 1729 consecutive cirrhotic patients with various forms of ADs admitted to the Department of Gastroenterology at SHHMU between August 1, 2021 and August 31, 2023 were screened, and 1608 patients were excluded, resulting in a total of 121 cirrhotic patients with ACLF participating in the study. The patients’ baseline characteristics in the three cohorts are shown in Table 1.

Table 1 Baseline characteristics of patients with Acute-on-chronic liver failure in different cohorts.
Baseline characteristicsMIMIC cohort
External validation cohorts
Derivation set (n = 938)
Validation set (n = 313)
eICU (n = 551)
SHHMU (n = 121)
Age (yr)59 (52-68)56 (53-66)57 (50-64)58 ± 13
Male, n (%)617 (65.8)202 (64.5)334 (60.6)81 (66.9)
Race, n (%)
White613 (65.4)a209 (66.8)448 (81.3)Eastern Asian
Non white325 (34.6)a104 (33.2)103 (18.7)Eastern Asian
Etiology of cirrhosis, n (%)
Alcohol524 (55.9)b180 (57.5)376 (68.2)43 (35.5)
Non-alcohol414 (44.1)b133 (42.5)175 (31.8)78 (64.5)
AD at admission, n (%)
Ascites520 (55.4)a,b173 (55.3)169 (30.7)32 (26.4)
Hepatic encephalopathy390 (41.6)b136 (43.5)156 (28.3)31 (25.6)
Bacterial infection422 (45.0)b152 (48.6)216 (39.2)16 (13.2)
Acute variceal bleeding75 (8.0)a,b34 (10.9)127 (23.0)42 (34.7)
Laboratory indicators
WBC (109/L)12 (8-18)b13 (9-18)10 (6-14)6 (5-11)
Hemoglobin85 (73-100)b83 (72-98)88 (75-103)92 (77-107)
Platelet (109/L)81 (50-135)72 (49-120)78 (49-126)75 (48-116)
Total bilirubin (mg/dL)4.1 (1.6-11.7)4.9 (1.8-12.3)4.0 (1.5-12.9)6.2 (1.6-17.5)
Albumin (g/dL)2.9 (2.4-3.3)2.9 (2.4-3.4)2.8 (2.2-3.3)2.9 ± 0.6
ALT (U/L)39 (22-98)b39 (23-101)36 (21-97)34 (16-64)
AST (U/L)83 (44-216)b94 (47-266)91 (43-253)62 (35-138)
INR2.1 (1.6-2.8)a,b2.0 (1.6-2.7)1.7 (1.4-2.4)1.7 (1.2-2.6)
Prothrombin time (s)22 (17-30)b22 (17-29)21 (16-28)19 (14-29)
Serum creatinine (mg/dL)2.1 (1.3-3.4)2.0 (1.2-3.2)2.0 (1.1-3.2)2.1 (1.1-3.0)
Serum sodium (mEq/L)135 (131-139)135 (131-139)137 (133-142)134 ± 7
Serum potassium (mEq/L)4.6 (4.1-5.3)a,b4.6 (4.2-5.4)4.0 (3.6-4.6)4.2 (3.7-4.7)
Organ failure, n (%)
Circulatory failure382 (40.7)a,b148 (47.3)305 (55.4)18 (14.9)
Respiratory failure427 (45.5)a,b156 (49.8)162 (29.4)22 (18.2)
Cerebral failure129 (13.8)a,b46 (14.7)223 (40.5)38 (31.4)
Renal failure658 (70.1)a,b201 (64.2)280 (50.8)75 (62.0)
Coagulation failure332 (35.4)b106 (33.9)131 (23.8)37 (30.6)
Liver failure233 (24.8)a,b82 (26.2)273 (49.5)54 (44.6)
Prognostic scores at admission
MELD28 (22-34)a,b27 (21-34)25 ± 1025 (18-31)
MELD-Na31 (23-40)b31 (22-40)27 (19-35)30 (21-38)
CLIF-C ACLF58 (51-64)b58 (52-64)50 (45-57)47 (42-54)
Liver transplantation, n (%)44 (4.7)11 (3.5)24 (4.4)2 (1.7)
ACLF grade, n (%)
Grade 1266 (28.4)a86 (27.5)263 (46.3)30 (33.1)
Grade 2317 (33.8)105 (33.5)177 (31.1)50 (41.3)
Grade 3355 (37.8)a122 (39.0)128 (22.6)41 (33.9)
28-day mortality, n (%)376 (40.1)122 (39.0)--46 (38.0)
90-day mortality, n (%)465 (49.6)144 (46.0)--59 (48.7)
In-ICU mortality, n (%)----112 (20.3)--
In-hospital mortality, n (%)----179 (32.4)--
Development of a new prognostic model for patients with ACLF

In the derivation set of MIMIC cohort, significant variables in univariate analysis included each OF defined by CLIF-OF score, ln (age), ln [mean arterial pressure (MAP)], ln (WBC count), ln (hemoglobin), ln (platelet count), ln (TB), ln [aspartate aminotransferase (AST)], ln (INR), ln (sodium level) and ln (potassium level), see Table 2. As the OFs criteria in CLIF-OF score determining CLIF-C ACLF with the maximum weight were proposed to have some limitations in clinical application, such as a ceiling effect of serum bilirubin and INR, and subjective variability in determining use of vasopressors, we used ln (TB), ln (INR) and ln (MAP) to reflect the state of liver, coagulation system and circulatory system, respectively. As renal replacement therapy was also a significant criterion in defining renal failure, we remained the renal failure criterion in CLIF-OF score. Respiratory and cerebral failure were defined according to CLIF-OF criteria. In addition, significant variables not indicating OF in the univariate analysis were also included in the multivariate analysis.

Table 2 Risk factors for 28-day mortality in acute-on-chronic liver failure patients from Medical Information Mart for Intensive Care-derivation set.
VariableUnivariate analysis
Multivariate analysis
HR (95%CI)
P value
HR (95%CI)
P value
Female1.08 (0.88-1.33)0.47
Ln (age)2.18 (1.32-3.61)0.0029.14 (5.16-16.19)< 0.001
Race (Non-white)1.15 (0.93-1.41)0.20
Cirrhosis etiology (non-alcohol)1.00 (0.82-1.23)0.998
Ln (MAP)0.03 (0.01-0.06)< 0.0010.06 (0.03-0.14)< 0.001
Organ failures
Circulatory failure1.87 (1.53-2.29)< 0.001
Respiratory failure1.56 (1.27-1.93)< 0.0011.84 (1.48-2.29)< 0.001
Cerebral failure1.63 (1.26-2.11)< 0.0011.36 (1.05-1.77)0.02
Renal failure1.89 (1.53-2.34)< 0.0011.68 (1.36-2.09)< 0.001
Liver failure2.31 (1.67-2.50)< 0.001
Coagulation failure2.04 (1.87-2.84)< 0.001
Laboratory indicators
Ln (WBC)1.58 (1.33-1.88)< 0.0011.25 (1.05-2.10)0.01
Ln (hemoglobin)0.65 (0.44-0.97)0.04
Ln (platelet)0.84 (0.73-0.97)0.02
Ln (TB)1.50 (1.38-1.63)< 0.0011.57 (1.42-1.73)< 0.001
Ln (Albumin)0.68 (0.45-1.04)0.07
Ln (ALT)1.04 (0.97-1.12)0.29
Ln (AST)1.09 (1.02-1.17)0.01
Ln (INR)1.27 (1.20-1.33)< 0.0011.82 (1.43-2.32)< 0.001
Ln (sodium)0.04 (0.01-0.23)< 0.001
Ln (potassium)2.05 (1.23-3.41)0.0061.84 (1.10-3.07)0.02

Results of the multivariate analysis were as follows: ln (age) (HR: 9.14, 95%CI: 5.16-16.19, P < 0.001), ln (WBC) (HR: 1.25, 95%CI: 1.05-2.10, P = 0.01), ln (TB) (HR: 1.57, 95%CI: 1.42-1.73, P < 0.001), ln (INR) (HR: 1.82, 95%CI: 1.43-2.32, P < 0.001), ln (potassium) (HR: 1.84, 95%CI: 1.10-3.07, P = 0.02), ln (MAP) (HR: 0.06, 95%CI: 0.03-0.14, P < 0.001), respiratory failure (HR: 2.74, 95%CI: 1.54-4.88, P < 0.001), cerebral failure (HR: 1.36, 95%CI: 1.05-1.77, P = 0.02) and renal failure (HR: 1.68, 95%CI: 1.36-2.09, P < 0.001) remained in the final regression model (Figure 1).

Figure 1
Figure 1 Forest plot showing independent risk factors for 28-day mortality in patients with acute-on-chronic liver failure. MAP: Mean arterial pressure; WBC: White blood cell; TB: Total bilirubin; INR: International normalized ratio.

Based on the coefficients of the above mentioned independent variables in the final regression model, the following new prognostic model for ACLF patients hospitalized in the ICU, MIMIC ACLF, was developed: MIMIC ACLF = ln (age) × 2.2 + presence of renal failure × 0.51 – ln (MAP) × 2.7 + presence of respiratory failure × 0.6 + presence of cerebral failure × 0.31 + ln (WBC) × 0.22 + ln (TB) × 0.44 + ln (INR) × 0.59 + ln (potassium) × 0.59. The probability of death at time “t” can be estimated as P = 1 - e-CI(t) × exp [β(t) × MIMIC ACLF score]. CI(t) and β(t) are the cumulative baseline hazard and score coefficient estimated by the model fitted for time “t”. At the main time, they are as follows: CI (28) = 0.281, β (28) = 0.9987; CI (90) = 0.443, β (90) = 0.90.

Prediction accuracy of the MIMIC ACLF model

Discrimination: To determine the discrimination ability of MIMIC ACLF, we plotted the ROC curve and calculated the AUC. The AUC of MIMIC ACLF for the 28/90-day mortality in patients with ACLF were 0.81/0.79, which were significantly greater than those of CLIF-C ACLF (0.76/0.74), MELD (0.73/0.71) and MELD-Na (0.72/0.70; all P < 0.001; Figure 2).

Figure 2
Figure 2 Receiver operating characteristic curve of prognostic scores for mortality in derivation set. A: Receiver operating characteristic (ROC)curve for 28-day mortality; B: ROC curve for 90-day mortality. AUC: Area under the curve; MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium.

Calibration: To determine the calibration ability of MIMIC ACLF, we performed Hosmer-Lemeshow test and plotted the calibration curves. The actual and predicted 28/90-day survival probabilities were highly consistent across the deciles of MIMIC ACLF score (Hosmer-Lemeshow test X2 = 5.26/8.46, P = 0.73/0.39; Brier score = 0.172/0.188; R2 = 0.364/0.315; Figure 3; Table 3). Calibration performance of CLIF-C ACLF were slightly inferior to that of MIMIC ACLF (Figure 3). MELD and MELD-Na, especially the latter obviously underestimated the 28-day and 90-day mortality in ACLF patients (Figure 3).

Figure 3
Figure 3 Calibration ability of prognostic scores for mortality in derivation set. A-D: Calibration for 28-day mortality [Medical Information Mart for Intensive Care (MIMIC) acute-on-chronic liver failure (ACLF; A), Chronic Liver Failure Consortium (CLIF-C) ACLF (B), Model for End-stage Liver (MELD, C), and MELD-Na (D)]; E-H: Calibration for 90-day mortality [MIMIC ACLF (E), CLIF-C ACLF (F), MELD (G), and MELD-Na (H)].
Table 3 Predictive values of prognostic scores for 28-day mortality in patients with acute-on-chronic liver failure.
Scores
Youden index
Cutoff value
SEN (%)
SPE (%)
PPV (%)
NPV (%)
Brier
score
R2 value
P in H-L test
Derivation set in MIMIC cohortDevelopment of MIMIC ACLF score
MIMIC ACLF0.480.5771.8175.9866.780.10.170.360.73
CLIF-C ACLF0.405965.4374.5663.276.30.190.260.70
MELD0.382773.1465.1258.478.40.200.200.04
MELD-Na0.36 2975.5359.9655.878.60.210.180.11
Validation set in MIMIC cohortInternal validation
MIMIC ACLF0.46 0.3281.9764.4069.584.80.170.360.26
CLIF-C ACLF0.406155.7484.2969.474.90.190.260.92
MELD0.37 2772.1364.4056.478.30.200.210.67
MELD-Na0.353072.9562.30 55.378.30.200.230.09
SHHMU cohort External validation
MIMIC ACLF0.49 1.5165.2284.0071.479.70.170.340.84
CLIF-C ACLF0.544971.7482.6771.782.7 0.170.350.14
MELD0.303336.9693.33 77.3 70.70.210.130.08
MELD-Na0.443460.8782.6768.377.50.200.220.52
DCA

To determine the clinical utility of MIMIC ACLF, we performed the decision curves analysis. The net benefit with MIMIC ACLF was greater than that indicated by the MELD, MELD-Na and CLIF-C ACLF in the entire range of the threshold probability (Figure 4), which indicated that MIMIC ACLF had superior clinical utility to the three existing prognostic scores.

Figure 4
Figure 4 Decision curve analysis of prognostic scores for mortality in derivation set of Medical Information Mart for Intensive Care cohort. A: Decision curve analysis (DCA) for 28-day mortality; B: DCA for 90-day mortality. MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium; ACLF: Acute-on-chronic liver failure.
Risk stratification

To stratify patients with ACLF according to MIMIC ACLF score, we performed survival analysis on enrolled patients based on the two optimal cutoff values (0.44 and 1.55) of MIMIC ACLF score obtained through X-tile software (version 3.6.1; Yale University, United States). The results showed that a total of 90 (18.7%)/137 (28.4%), 132 (53.9%)/208 (65.2%) and 114 (83.2%)/120 (87.6%) patients among those with new score of ≤ 0.44, 0.45-1.54 and ≥ 1.55 died during a 28-day/90-day follow-up period, respectively (P value in log-rank test < 0.0001; Figure 5). Patients with MIMIC ACLF score of ≤ 0.44, 0.45-1.54 and ≥ 1.55 were thus stratified into low, moderate and high risk of death groups, respectively.

Figure 5
Figure 5 Survival analysis based on Medical Information Mart for Intensive Care acute-on-chronic liver failure score for mortality in derivation set of Medical Information Mart for Intensive Care cohort. A: Survival analysis for 28-day mortality; B: Survival analysis for 90-day mortality. MIMIC: Medical Information Mart for Intensive Care; ACLF: Acute-on-chronic liver failure.
Validation of MIMIC ACLF model

Internal validation: In the internal validation cohort, the AUC of MIMIC ACLF for 28-day mortality (0.80) was significantly greater than those of CLIF-C ACLF (0.75, P = 0.01), MELD (0.74, P = 0.02) and MELD-Na (0.75, P = 0.05; Figure 6A). With regard to 90-day mortality, the AUC of MIMIC ACLF (0.76) was significantly or numerically greater than that of CLIF-C ACLF (0.71, P = 0.02), MELD (0.71, P = 0.07) and MELD-Na (0.72, P = 0.17; Figure 6B).

Figure 6
Figure 6 Receiver operating characteristic curve of prognostic scores for mortality in validation set of Medical Information Mart for Intensive Care cohort. A: Receiver operating characteristic (ROC) curve for 28-day mortality; B: ROC curve for 90-day mortality. AUC: Area under the curve; MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium; ACLF: Acute-on-chronic liver failure.

The actual and predicted 28-day survival probability were highly consistent across the sextile of MIMIC ACLF score (Hosmer-Lemeshow test X2 = 5.26 P = 0.73; Brier score = 0.172; R2 = 0.364; Figure 7A-D; Table 3). The calibration performances of MELD, MELD-Na and CLIF-C ACLF were inferior to that indicated by MIMIC ACLF (Figure 7). With regard to the 90-day mortality, the performances of all prognostic scores were similar and satisfactory (Figure 7E-H; Table 3).

Figure 7
Figure 7 Calibration ability of prognostic scores for mortality in validation set of Medical Information Mart for Intensive Care cohort. A-D: Calibration for 28-day mortality [Medical Information Mart for Intensive Care (MIMIC) acute-on-chronic liver failure (ACLF, A), Chronic Liver Failure Consortium (CLIF-C) ACLF (B), Model for End-stage Liver (MELD, C), and MELD-Na (D)]; E-H: Calibration for 90-day mortality [MIMIC ACLF (E), CLIF-C ACLF (F), MELD (G), and MELD-Na (H)].

DCA showed that the net benefit with MIMIC ACLF was greater than that indicated by MELD, MELD-Na and CLIF-C ACLF in almost the entire range of threshold probabilities (Figure 8).

Figure 8
Figure 8 Decision curve analysis of prognostic scores for mortality in validation set of Medical Information Mart for Intensive Care cohort. A: Decision curve analysis (DCA) for 28-day mortality; B: DCA for 90-day mortality. MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium; ACLF: Acute-on-chronic liver failure.

Survival analysis revealed that a total of 33 (20.4%)/47 (29.0%), 56 (49.6%)/62 (54.9%) and 33 (86.8%)/35 (92.1%) patients in the low, moderate and high-risk groups died during the 28-day/90-day follow-up period, respectively (P value in log-rank test < 0.0001; Figure 9).

Figure 9
Figure 9 Internal validation of Medical Information Mart for Intensive Care acute-on-chronic liver failure score-based risk stratification. A: Risk stratification for 28-day mortality in patients with acute-on-chronic liver failure (ACLF); B: Risk stratification for 90-day mortality in patients with ACLF. MIMIC: Medical Information Mart for Intensive Care; ACLF: Acute-on-chronic liver failure.
External validation

SHHMU cohort: In the SHHMU cohort, the AUC of MIMIC ACLF for 28/90 day mortality (0.80/0.78) was comparable with that of CLIF-C ACLF (0.82/0.80, P > 0.05) but significantly or numerically greater than that of MELD (0.65/0.67, P < 0.05) and MELD-Na (0.74/0.73, P > 0.05) (Figure 10A and B). The calibration curve showed that the calibration ability of MIMIC ACLF for 28-day mortality was superior to that indicated by MELD, MELD-Na and CLIF-C ACLF; the calibration ability of MIMIC ACLF for 90-day mortality was similar with that of MELD but superior to that indicated by MELD-Na and CLIF-C ACLF (Figure 10C and D; Table 3). DCA showed that the net benefit of MIMIC ACLF was comparable with that of CLIF-C ACLF but greater than indicated by MELD and MELD-Na (Figure 10E and F). Survival analysis showed that a total of 33 (20.4%)/47 (29.0%), 56 (49.6%)/62 (54.9%) and 33 (86.8%)/35 (92.1%) patients among those stratified into low, moderate and high risk groups died during a 28-day/90-day follow-up period, respectively (P value in log-rank test < 0.0001; Figure 10G and H).

Figure 10
Figure 10  External validation of Medical Information Mart for Intensive Care acute-on-chronic liver failure model in the Second Hospital of Hebei Medical University cohort. A: Receiver operating characteristic (ROC) curve for 28-day mortality; B: ROC curve for 90-day mortality; C: Calibration curve for 28-day mortality; D: Calibration curve for 90-day mortality; E: Decision curve analysis for 28-day mortality; F: Decision curve analysis for 90-day mortality; G: Survival analysis for 28-day mortality; H: Survival analysis for 90-day mortality. AUC: Aera under the curve; ROC: Receiver operating characteristic; MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium; ACLF: Acute-on-chronic liver failure.

eICU cohort: In the eICU cohort, the AUC (0.75) of MIMIC ACLF for in-ICU mortality was equal to CLIF-C ACLF (0.75, P > 0.05), but significantly or numerically greater than that indicated by MELD-Na (0.67, P = 0.006), MELD (0.70, P > 0.05) and APACHE (0.71, P > 0.05; Figure 11A). The AUC (0.76) of MIMIC ACLF for in-hospital mortality was comparable to CLIF-C ACLF (0.77, P > 0.05), significantly or numerically greater than that indicated by MELD (0.65/0.67, P < 0.05), MELD-Na, and APACHE (0.74/0.73, P > 0.05; Figure 11B). The calibration curve showed that the calibration ability of MIMIC ACLF for in-ICU mortality is similar to MELD and CLIF-C ACLF, but better than MELD-Na and APACHE (Figure 12A-E); The calibration ability of MIMIC ACLF for in-hospital mortality is similar to MELD, MELD-Na, APACHE, and CLIF-C ACLF (Figure 12F-J). The overall performance of MIMIC ACLF in predicting ICU mortality in ACLF patients (Brier score = 0.14, R2 value = 0.21) is superior to CLIF-C ACLF (Brier score = 0.14, R2 value = 0.20), MELD (Brier score = 0.15, R2 value = 0.13), MELD-Na (Brier score = 0.15, R2 value = 0.09), and APACHE (Brier score = 0.15, R2 value = 0.14; Figure 12A-E); The overall performance of MIMIC ACLF in predicting in-hospital mortality (Brier score = 0.18, R2 value = 0.26) was slightly lower than CLIF-C ACLF (Brier score = 0.17, R2 value = 0.28), but better than MELD (Brier score = 0.19, R2 value = 0.18), MELD-Na (Brier score = 0.20, R2 value = 0.14), and APACHE (Brier score = 0.20, R2 value = 0.15; Figure 12F-J). DCA showed that the net benefit of MIMIC ACLF for ICU mortality is comparable to CLIF-C ACLF, but greater than that indicated by MELD, MELD-Na, and APACHE (Figure 13A). The net benefit of MIMIC ACLF for in-hospital mortality is slightly lower than CLIF-C ACLF, but greater than that indicated by MELD, MELD-Na, and APACHE (Figure 13B).

Figure 11
Figure 11  Receiver operating characteristic curves of prognostic scores for mortality in electronic intensive care unit cohort. A: Receiver operating characteristic (ROC) curve for In-intensive care unit mortality; B: ROC curve for In-hospital mortality. ICU: Intensive care unit; AUC: Aera under the curve; ROC: Receiver operating characteristic; MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium; ACLF: Acute-on-chronic liver failure.
Figure 12
Figure 12  Calibration curves of prognostic scores for mortality in electronic intensive care unit cohort. A-E: In-intensive care unit mortality [Medical Information Mart for Intensive Care (MIMIC) acute-on-chronic liver failure (ACLF, A), Chronic Liver Failure Consortium (CLIF-C) ACLF (B), Model for End-stage Liver (MELD, C), MELD-Na (D) and APACHE (E)]; F-J: In-Hospital mortality [MIMIC ACLF (F), CLIF-C ACLF (G), MELD (H), MELD-Na (I) and APACHE (J)]. ICU: Intensive care unit; OS: Overall survival.
Figure 13
Figure 13  Decision curve analysis of prognostic scores for mortality in electronic intensive care unit cohort. A: In-intensive care unit mortality; B: In-Hospital mortality. MIMIC: Medical Information Mart for Intensive Care; MELD: Model for End-stage Liver; CLIF-C: Chronic Liver Failure Consortium; ACLF: Acute-on-chronic liver failure.
Online calculator

To facilitate the clinical application of MIMIC ACLF prognostic model, we constructed an online calculator based on MIMIC ACLF model (https://www.scidb.cn/en/anonymous/anllWU52). After the easily available variables (i.e., age, WBC, serum potassium, TB, INR, MAP, respiratory failure, cerebral failure and renal failure) are input into the MIMIC ACLF online calculator, predicted individual 28/90-day mortality in ACLF patients can be easily obtained (Figure 14).

Figure 14
Figure 14  The online calculator based on Medical Information Mart for Intensive Care acute-on-chronic liver failure prognostic model. MIMIC: Medical Information Mart for Intensive Care; ACLF: Acute-on-chronic liver failure; INR: International normalized ratio.
DISCUSSION

ACLF is the most severe stage of chronic liver disease with single/multiple OF (s) and high short-term mortality. Patients with ACLF usually need to be hospitalized in the ICU for monitoring of their condition and organ support therapy. Reasonable treatment for ALCF should be specified based on the corresponding prognosis. Therefore, an accurate and robust prognostic score is very important for decision-making by clinicians in ICU. At present, existing prognostic scores used in ICU mainly include CTP, MELD and MELD-Na and CLIF-C ACLF. However, these scores either do not reflect the impact of multiple OFs for ACLF or have some limitations, resulting in a limited predictive accuracy. In this study, we developed a new prognostic model (MIMIC ACLF) using medical data in MIMIC database for patients with ACLF. MIMIC ACLF not only exhibited a satisfactory predictive accuracy and clinical utility in MIMIC cohort, but also performed well in the external single and multiple-center validation cohorts. In addition, we constructed an online calculator based on MIMIC ACLF to facilitate the its application in clinical practice.

Compared with results of recent studies, the short-term mortality in ACLF patients included in this study was highly consistent. In the derivation cohort, 28/90-day mortality in all patients with ACLF, ACLF grade 1, ACLF grade 2 and ACLF grade 3 were 40.1%/49.6%, 20.7%/33.1%, 31.5%/40.1% and 62.3%/70.4%, respectively. This is highly consistent with the result in a recent large sample observational study including 867 European and Canadian ACLF patients hospitalized in ICU where the 28/90-day mortality in all patients with ACLF, ACLF grade 1, ACLF grade 2 and ACLF grade 3 were 43.9%/54.0%, 22.0%/33.0%, 30.0%/40.0% and 64.0%/74.0%, respectively[10]. Compared to the mortality in another recent large sample retrospective cohort study in United States[27] where the 28-day/90-day mortality in all ACLF, ACLF grade 1, grade 2 and ACLF grade 3 were 25.5%/40.0%, 16.9%/30.8%, 26.8%/41.6% and 53.3%/68.8%, respectively, our mortality seems somewhat higher. This might be due to the fact that they included hospitalized patients with ACLF in both ICU and general wards while we only included those hospitalized in ICU. In summary, the diagnosis/grade of ACLF which plays an important role in determining the mortality in ACLF patients was accurate enough to lay a foundation for the subsequent analysis in this study.

Although the MIMIC ACLF prognostic model was developed based on the CLIF-C ACLF model, it overcomes the limitations of the CLIF-C ACLF model. There are 9 variables that constitute MIMIC ACLF, namely age, WBC count, serum potassium, TB, INR, MAP, respiratory failure, cerebral failure and renal failure. The natural logarithms of TB, INR and MAP reflect the weight of liver failure, coagulation failure and circulatory failure, respectively, on the short-term mortality of patients with ACLF. In this way, the proposed shortcomings of CLIF-C ACLF, such as ceiling effect of TB and INR, subjective variability in determining use of vasopressors can be avoided. In addition, the presence/absence of cerebral failure, renal failure and respiration failure as defined by the CLIF-OF criterion in CLIF-C ACLF was also included in MIMIC ACLF. In this way, the limitation of difficulty in distinguishing HE grade 1 and grade 0 in CLIF-C ACLF can also be avoided because it is relatively simple to distinguish between presence and absence of cerebral failure (HE grade 3 or 4 vs HE grade 0). Similar to the CANONIC study, age and WBC were significantly and positively associated with the mortality in patients with ACLF, indicating that ACLF is a distinct syndrome highly associated with systemic inflammation[2]. A new finding is that the natural logarithm of serum potassium was identified as an independent risk factor for the 28-day mortality in ACLF patients (HR = 1.84, P = 0.02). This finding coincided with that of a recent study in which presence of hyperkalemia during admission was independently associated with the 90-day mortality in ACLF patients (HR = 2.4, P < 0.001)[28]. To date, data on the impact of serum potassium on the prognosis of ACLF patients are scarce. We assume that hyperkalemia might represent a more severe condition involving intensive systemic inflammation, renal failure, liver failure and sarcopenia[26]. However, the pathophysiological association between hyperkalemia and poor prognosis of ACLF patients remains to be elucidated.

An ideal prognostic score should perform well in the following aspects: discrimination, calibration and DCA. Discrimination refers to the ability to stratify patients according to their risk of developing the outcome. Calibration refers to the ability to predict absolute risks (how closely the predicted probabilities agree with the actual outcomes). The DCA is a suitable analytical method evaluating which prognostic score benefits patients most and has the best clinical utility. In the MIMIC cohort, whether in the derivation or validation set, MIIMC ACLF performed well and outperformed existing prognostic scores, including CLIF-C ACLF, in the assessment of discrimination, calibration and clinical utility for 28/90 d mortality in ACLF patients. MELD-Na markedly underestimated the 28/90-day mortality in ACLF patients, which was consistent with the results in recent large sample studies[9,29]. According to the multiple-center external validation using data from the eICU cohort, the predictive accuracy of MIMIC ACLF for the in-ICU and in-hospital mortality was comparable to that of CLIF-C ACLF but superior to that of traditional scores, such as MELD, MELD-Na and APACHE. In addition, we also validated the prediction performance of MIMIC ACLF in SHHMU, a Chinese ACLF cohort in which the hospitalization location, demographic characteristics and cirrhosis etiology differed from those in western cohorts. Results were that MIMIC ACLF combined with CLIF-C ACLF performed well, outperforming CTP, MELD and MELD-Na in the prediction of 28/90 mortality. In conclusion, MIMIC ACLF model showed a prediction accuracy comparable to that of CLIF-C ACLF score but outperformed other existing scores for short-term mortality in ACLF patients hospitalized both in the ICU and general ward environments.

Importantly, in this study, patients with ACLF were stratified according to the MIMIC ACLF score. Patients with MIMIC ACLF score of ≤ 0.44, 0.45-1.54 and ≥ 1.55 were respectively stratified into low, moderate and high risk of death groups. The 28/90-day mortality significantly increased from low (18.7%/28.4%) to moderate (53.9%/65.2%) to high risk groups (83.2%/87.6%; P <0.0001), which was confirmed in the internal and external validation cohorts. Compared with the risk stratification with CLIF-C ACLF score (28/90-day mortality in ACLF grade 1, grade 2 and grade 3: 20.7%/33.1%, 31.5%/40.1% and 62.3%/70.4%, respectively), a lower and higher mortality rate were respectively seen in our low and high risk groups than that in the equal risk grades of CLIF-C ACLF. In addition, we also developed an online calculator of MIMIC ACLF score to make the individual mortality prediction easier. This online calculator, combined with the risk grades, will be very useful in assisting clinicians in ICU to evaluate the prognosis of patients with ACLF. After risk stratification, patients in low and moderate risk groups can be considered for ongoing intensive treatment without hesitation in order to prevent the progression of ACLF, and meanwhile LT assessment should be performed as soon as possible[5,30]; for those in high risk group, if not the LT candidates, a careful consideration of transition to palliation should be discussed between patient families and ICU clinicians after a short treatment trial[31,32].

Our study has two limitations that warrant consideration. First, as this study was a retrospective cohort study, selection, information and confounding bias are inevitable. For example, diagnosis of covert HE (minimal HE and grade Ⅰ) might be partly affected by the subjective factors of observers; distinguishing between respiratory failure and cerebral failure became difficult when mechanical ventilation therapy was provided because it was hard to determine the exact indication for mechanical ventilation (respiratory failure, airway protection due to cerebral failure or both). Second, the sample size in the SHHMU cohort was relatively small. However, we are planning to conduct a multi-center and longer-term study to continue externally validating the MIMIC ACLF prognostic model.

CONCLUSION

In conclusion, we developed and validated a new prognostic model (MIMIC ACLF) for cirrhotic patients with ACLF hospitalized in ICU. MIMIC ACLF overcomes the shortcomings of existing prognostic scores and has demonstrated a satisfactory ability to predict the short-term mortality in patients with ACLF. The MIMIC ACLF based risk stratification and online calculator could be useful for assisting in risk evaluation and guiding rational management of patients with ACLF. More large-sample and prospective studies are needed to validate the predictive accuracy of this new model.

ACKNOWLEDGEMENTS

We would like to thank the researchers in Massachusetts Institute of Technology and medical staff in Beth Israel Deaconess Medical Center for their contribution to the MIMIC database. We would also like to thank the Philips eICU Research Institute and Philips Healthcare for their contribution to the eICU database and thank patients in the SHHMU cohort for their contribution to the SHHMU data.

Footnotes

Provenance and peer review: Unsolicited article; Externally peer reviewed.

Peer-review model: Single blind

Specialty type: Gastroenterology and hepatology

Country of origin: China

Peer-review report’s classification

Scientific Quality: Grade A

Novelty: Grade A

Creativity or Innovation: Grade A

Scientific Significance: Grade A

P-Reviewer: Rodrigues AT, Brazil S-Editor: Lin C L-Editor: A P-Editor: Chen YX

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