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Prediction model of ICU readmission in Chinese patients with acute type A aortic dissection: a retrospective study
BMC Medical Informatics and Decision Making volume 24, Article number: 358 (2024)
Abstract
Background
Readmission to the intensive care unit (ICU) remains a severe challenge, leading to higher rates of death and a greater financial burden. This study aimed to develop a nomogram-based prediction model for individuals with acute type A aortic dissection (ATAAD).
Methods
A total of 846 ATAAD patients were retrospectively enrolled between May 2014 and October 2021. Logistic regression was employed to identify the independent risk factors. The prediction model was evaluated using the Hosmer–Lemeshow (H–L) test, the calibration curve, and the area under the receiver operating characteristic curve (AUC). Decision curve analysis (DCA) was used to assess the clinical utility.
Results
57 (6.7%) ATAAD patients were readmitted to ICU following their release from the ICU. ICU readmission was predicted with age ≥ 65 years old, body mass index (BMI) ≥ 28 kg/m2, tracheotomy, continuous renal replacement therapy (CRRT), and the length of initial ICU stay were predictors of ICU readmission. The AUC was 0.837 (95%CI: 0.789–0.884) and the model fit the data well (H–L test, P = 0.519). DCA also demonstrated good clinical practicability.
Conclusions
This prediction model may be helpful for clinicians to assess the risk of ICU readmission, and facilitate the early identification of ATAAD patients at high risk.
Background
Acute type A aortic dissection (ATAAD) is a rare and life-threatening cardiovascular emergency, with challenging treatment for both cardiac surgeons and intensive care physicians [1, 2]. Readmission to the intensive care unit (ICU) after surgery for ATAAD is still a serious concern, which leads to 10 times higher mortality, worse quality of life, and increased socioeconomic burden [3].
The Society for Critical Care Medicine in the United States has advocated ICU readmission as a quality indicator [4]. Patients undergoing aortic surgery have a higher ICU readmission rate compared to other cardiovascular surgeries [5]. However, the relevant research in ATAAD is limited. Reported risk factors of readmission to the ICU, especially after cardiac surgery, are controversial [2, 6]. Accordingly, this study attempts to identify risk factors of ICU readmission in ATAAD patients and develops a prediction model that would assist clinicians to identifying high-risk patients.
Methods
Study design and population
A retrospective study was conducted on ATAAD patients between May 2014 and October 2021 at a hospital in Fujian Province, China. Patients older than 18 and diagnosed with ATAAD by computed tomography angiography were enrolled. Patients were excluded from the study if they (1) did not receive surgery; (2) died before being discharged from the ICU or on the general ward after being discharged from their initial ICU stay; (3) gave up treatment or were transferred to other medical institutions; (4) had incomplete clinical information. The hospital institutional review board approved this retrospective study, with a waiver of informed consent (2022KY128).
Data collection
In this study, ICU readmission was defined as a transfer from the ICU to the wards and then back to the ICU during the same hospitalization [7]. For ATAAD patients who were readmitted to the ICU, only the first admissions were included in the analysis. Collected variables were chosen based on a combination of clinical expertise and evidence from the literature. All data were retrospectively collected from the electronic medical record system.
Preoperative variables included gender, age, diabetes mellitus, hypertension, Marfan’s syndrome, previous cardiac surgery, body mass index (BMI), heart rate, systolic blood pressure, diastolic blood pressure, and left ventricular ejection fraction (LVEF). Intraoperative variables included the surgery with coronary artery bypass surgery (CABG), operating time, cardiopulmonary bypass (CPB) time, and aortic cross-clamping time. Postoperative variables included tracheotomy, continuous renal replacement therapy (CRRT), and prolonged mechanical ventilation (PMV), white blood cell, red blood cell, platelet, hemoglobin, systemic inflammatory response index (SIRI), the length of initial ICU stay, et al. The last laboratory data before discharge from the ICU and the length of initial ICU stay were also collected.
PMV was identified as the duration of mechanical ventilation use > 48 h [8]. In this study, the prediction model of ICU readmission was developed by variables spanning from hospital admission to ICU discharge. Variables required complex calculations were not easy to use for planning ICU discharge [9]. Therefore, we involved easily accessible and broadly available data to construct this model for clinical application.
Over half of ICU beds are occupied by the elderly (≥ 65 years old) [10]. On the other hand, to facilitate the use of the constructed model, age was treated as a categorical variable (≥ 65 years vs. < 65 years) in the process of modeling. In addition, BMI was also categorized as obese (BMI > 28 kg/m2) and non-obese groups according to the Working Group on Obesity in China [11].
Transfer practices
The standard perioperative and surgical management protocols were performed in ATAAD patients. ATAAD patients are all admitted to the cardiovascular ICU for follow-up treatment after surgery. Following the safe staffing policy, the ICU is staffed adequately with the required number of doctors and nurses. The decisions of ICU discharge and ICU readmission were made by the attending physicians and intensivists based on the patient’s health status. Patients were required to meet the following conditions before ICU discharge: stable vital signs, hemodynamically stable, no serious organ dysfunction, spontaneous breathing, and acceptable blood gas analysis index. The ATAAD patients discharged from the ICU were handed over to the surgical team for continued post-operative care in the cardiac surgical ward.
Statistical analysis
The software SPSS 25.0 was used for data analysis. Normal continuous variables were presented as mean ± standard and were compared using Student’s t-test. The non-normal continuous variables were expressed as the median and interquartile range (IQR) and were compared by the Mann–Whitney U test. Categorical variables were summarized using frequency counts and percentages, and tested by the chi-square or Fisher exact test. Variables with a p-value less than 0.05 in univariate analysis were integrated into the multivariate analysis and developed a logistic regression equation model to predict ICU readmission. R software (version 4.1.2) was used to draw the nomogram for visualizing the model. In the nomogram, the score corresponding to each predictor was determined based on the regression coefficients in the model and summed to obtain a total score. The total score corresponded to the risk probability of ICU readmission. The bootstrapping method was used for internal validation, which involved repeatedly extracting the same number of samples 1000 times from the database, then placing them back and evaluating the model in the generated new samples. The area under the receiver operating characteristic curve (AUC) was used to test the discrimination of the model. A tenfold cross validation was adopted for reliability of the model. Model fit was assessed via Hosmer–Lemeshow (H–L) test and calibration curve. Decision curve analysis (DCA) was used to evaluate the clinical net benefit of the prediction model.
Results
Patient characteristics and risk factors
A total of 923 samples were included, of which 77 were excluded, leaving 846 samples for the final analysis, shown in Fig. 1. After exclusions for incomplete data, 57 ATAAD patients (6.7%) were readmitted to the ICU after transfer to the ward.
The characteristics of ATAAD patients are shown in Table 1. 651 (77.0%) of participants were male and 110 (13.0%) were older than 65 years. ATAAD patients with bounce backs had longer operating time as compared to non-readmitted patients (337.25 ± 77.37 vs. 311.40 ± 82.78 min, P = 0.022), were more likely to receive CRRT (26.3% vs. 6.2%, P < 0.001) and tracheotomy (14.0% vs. 3.9%, P < 0.001). Compared to the non-readmission group, patients in the readmission group had higher BMI (26.24 ± 3.57 vs. 24.81 ± 3.23 kg/m2, P = 0.001). The results also revealed significant differences in the length of initial ICU stay between two groups (P < 0.001).
Prediction model
The univariate analysis showed that ≥ 65 years old, BMI ≥ 28 kg/m2, operating time, tracheotomy, CRRT, and the length of initial ICU stay were associated with ICU readmission (P < 0.05). There is no collinearity and low correlation among risk factors, with VIF values of variables ranging from 1.023 to 1.118. The multivariate regression model revealed that 5 variables were independent risk factors of ICU readmission in ATAAD patients, including ≥ 65 years old (OR = 2.168, P = 0.039), BMI ≥ 28 kg/m2 (OR = 2.268, P = 0.022), tracheotomy (OR = 6.003, P = 0.001), CRRT (OR = 2.859, P = 0.009), and the length of initial ICU stay (OR = 1.107, P < 0.001), reported in Table 2.
For visualization and convenience of clinical application, we constructed a nomogram combining the risk value and regression equation. The score of each variable was shown at the top of the scale, and a vertical line down from the total points row to obtain the risk probability. With an increased score, the risk of ICU readmission was additionally increased, presented in Fig. 2.
Qualitative characteristics of the prediction model
The AUC of the prediction model was 0.837 (95%CI: 0.789–0.884). The optimal cutoff value of 0.057 with a sensitivity of 77.2%, specificity of 76.6%, and accuracy of 76.6%. After 1000 bootstrap resamples for internal verification, the average AUC of this model was 0.836 (95%CI: 0.835–0.838). The results of tenfold cross validation demonstrated a mean absolute error of 0.114 and root mean square error of 0.234. The calibration curve also indicated acceptable agreement of the predicted probability with the actual observed probability, presented in Fig. 3. The DCA demonstrated that the benefit curve was higher than the extreme curves when the threshold probability was approximately 5%–52%, which meant the application of the nomogram model would add more benefit than either treat-all strategy and treat-none strategy, presented in Fig. 4.
Decision curve analyses of the model. X-axis: The threshold probability of ICU readmission at which the patient would be classified as being at high risk for being readmitted to the ICU. Y-axis: The net benefit represents that the benefits obtained from preventing ATAAD patients from ICU readmission exceed the potential harm caused by unnecessary prevention
Discussion
ICU readmission is regarded as a quality indicator of critical care, associated with higher in-hospital mortality, poorer long-term outcomes, and increased hospitalization costs [12]. The previous findings of being readmitted to cardiovascular ICU remain controversial, and research on ATAAD is lacking [13]. In this study, we included 5 variables to develop a nomogram to predict the risk of ICU readmission in ATAAD patients.
The average rate of ICU readmission for cardiac surgery patients ranges from 1.9% to 3.5% in large-sample investigations [2, 5]. However, we found that 6.7% of ATAAD patients were readmitted to ICU after surgery in this study, which is higher than the previous results. Patients with aorta surgery experienced higher ICU readmission than other cardiovascular diseases [5]. ATAAD is the most lethal aortic condition, however, most patients are referred from the other hospitals in developing countries and take longer times from onset to surgery with worse disease conditions [1, 14]. At the same time, compared to general cardiovascular surgery, the required surgery of ATAAD is more complex with a high incidence of severe postoperative complications, [15, 16] which may result in the relatively high incidence of bouncing back to ICU.
A study targeting Chinese patients undergoing cardiac surgery has shown that elderly individuals have a higher risk of readmission [17]. This is supported by our data. Post-ICU patients are at high risk for adverse events because of the severity of their illness and the complexity of care required. However, compared to young patients, elderly patients have an increased incidence of co-morbidities, poorer ability to meet physiological needs, and longer recovery times [18, 19], especially for ATAAD patients with open surgical repair. Consequently, readmitted patients tend to be older than those not readmitted [20].
Our results indicate that ATAAD patients with high BMI have a higher risk of being readmitted to ICU. In a previous study, for patients undergoing cardiac surgery, high BMI is associated with increased utilization of ICU resources and a high risk of ICU readmission, [21] which is also supported by our data. Aortic dissection patients with high BMI are prone to impaired mobility, balance, and physical function, with a higher incidence of obesity-associated comorbidities [22]. Therefore, the attending should pay more attention to ATAAD patients with high BMI on clinical rounds to prevent ICU readmission.
CRRT is the primary form of renal replacement therapy for patients with kidney injury for providing a slow, gentle, and continuous kidney support [23, 24]. A survey on heart valve surgery found that patients with renal failure have higher risk of ICU readmission [17]. In this study, we also found that ATAAD patients receiving CRRT treatment are also more likely to be readmitted. Clinicians should increase their awareness that how to prevent renal injury during the early postoperative period and avoid excessive use of CRRT.
Tracheotomy is considered the major characteristic of ICU readmission after discharge from critical care [25]. Consistent with the previous finding, ATAAD patients with tracheostomy had a higher risk of ICU readmission. Tracheostomy is indicated for anticipated prolonged ventilation and relief of airway obstruction, [26] however, may lead to complications such as hemorrhage and respiratory infections [27]. In addition, it can also pose an elevated risk of 30-day readmission after discharge from the hospital [9].
The length of initial ICU stay is considered one of the strongest risk factors of ICU readmission [7]. Our study also demonstrates the importance of the length of initial ICU stay in predicting the risk of readmission for ATAAD patients. Prolongation of exposure to the ICU may indicate higher severity of illness and worse physical conditions that increase the possibility of ICU readmission.
A few studies in the past have tried to develop machine learning models of ICU admission [28, 29]. However, tracing the process of these models is difficult for lacking transparency in analysis [30]. In clinical practice, the presence of interpretability barriers in machine learning models makes it difficult for clinicians to judge and guide their decisions [31]. Sean et al. [32] developed a prediction model through a survey of 10,799 patients with cardiac surgery. However, this model excludes patients undergoing complex operations on the aortic arch with more critical postoperative conditions. Given the limitations of previous models, this study has filled the gap in predicting ICU readmission of ATAAD patients. In this study, the AUC was 0.837, which is better than the study in cardiac surgery ICU (AUC = 0.81) and the study in surgical critical care (AUC = 0.78) [6, 7]. Compared with the previous model, [6] this prediction model in ATAAD supplements the collection of treatment information during the ICU period. This model maintains acceptable discrimination and calibration to quickly identify ATAAD patients at high risk of readmission.
The risk assessment of ICU readmission can be conducted before being transferred out of the ICU, for estimating the level of care required in the ward. Patients with higher risk can be discharged to wards with a better nursing-patient ratio for close monitoring and given proactive nursing plans to prevent condition deterioration. In addition, based on the model, rational application of CRRT and tracheotomy, and early transfer planning to avoid prolonged ICU stay all help to reduce the incidence of ICU readmission.
Limitations
This study still has the following several limitations. Based on the retrospectively collected data and the lack of information on the use of drugs such as antibiotics, there are inherent design biases in this study. With small sample size, our model needs to be further verified by large, multi-center, prospective cohort studies.
Conclusions
In this study, we identified the independent risk factors of ICU readmission in ATAAD patients. Based on these factors, we constructed a prediction model using nomogram. The AUC of the model was 0.837 and the model fit well in calibration curve. This model may provide a reference to identify ICU readmission in ATAAD patients.
Data availability
All data generated or analyzed during this study are included in the article.
Abbreviations
- ATAAD:
-
Acute type A aortic dissection
- ICU:
-
Intensive care unit
- BMI:
-
Body mass index
- LVEF:
-
Left ventricular ejection fraction
- CABG:
-
Coronary artery bypass surgery
- CPB:
-
Cardiopulmonary bypass
- CRRT:
-
Continuous renal replacement therapy
- PMV:
-
Prolonged mechanical ventilation
- IQR:
-
Interquartile range
- AUC:
-
Area under the receiver operating characteristic curve
- H-T test:
-
Hosmer–Lemeshow test
- DCA:
-
Decision curve analysis
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Acknowledgements
We would also like to thank the hospital for supporting data collection of this study.
Funding
This research was funded by Fujian Provincial Finance Special Project [grant number: 2021XH019], Key Laboratory of Cardio-Thoracic Surgery (Fujian Medical University), Fujian Province University, and The Fifth Batch of Hospital Key Discipline Construction Projects [grant number: 2022YYZDXK01].
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Contributions
YJ Lin and LW Chen designed and conceived the whole study. H Ni and YC Peng analyzed and interpreted the data. H Ni and Q Pan drafted the manuscript. ZL G and SL L collected the data. All authors provided an important revision of this manuscript.
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Ethics approval and consent to participate
This study was approved by the ethical review committee of the Fujian Medical University Union Hospital (2022KY128). The research ethics committee waived the requirement for informed consent for retrospective samples.
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All authors have given their consent for publication.
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The authors declare no competing interests.
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Ni, H., Peng, Y., Pan, Q. et al. Prediction model of ICU readmission in Chinese patients with acute type A aortic dissection: a retrospective study. BMC Med Inform Decis Mak 24, 358 (2024). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12911-024-02770-2
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DOI: https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12911-024-02770-2