Poor outcomes of delirium in the intensive care units are amplified by increasing age: A retrospective cohort study

doi:10.5847/wjem.j.1920-8642.2021.02.006

Abstract

Abstract:

BACKGROUND: Delirium in patients in intensive care units (ICUs) is an acute disturbance and fluctuation of cognition and consciousness. Though increasing age has been found to be related to ICU delirium, there is limited evidence of the effect of age on delirium outcomes. The aim of this study is to investigate the relationship between age categories and outcomes among ICU delirium patients.

METHODS: Data were extracted from the electronic ICU (eICU) Collaborative Research Database with records from 3,931 patients with delirium. Patients were classified into non-aged (<65 years), young-old (65-74 years), middle-old (75-84 years), and very-old (≥85 years) groups. A Cox regression model was built to examine the role of age in death in ICU and in hospital after controlling covariates.

RESULTS: The sample included 1,667 (42.4%) non-aged, 891 (22.7%) young-old, 848 (21.6%) middle-old, and 525 (13.3%) very-old patients. The ICU mortality rate was 8.3% and the hospital mortality rate was 15.4%. Compared with the non-aged group, the elderly patients (≥65 yeras) had higher mortality at ICU discharge (χ ²=13.726, P=0.001) and hospital discharge (χ ²=56.347, P<0.001). The Cox regression analysis showed that age was an independent risk factor for death at ICU discharge (hazard ratio [HR]=1.502, 1.675, 1.840, 95% confidence interval [CI] 1.138-1.983, 1.250-2.244, 1.260-2.687; P=0.004, 0.001, 0.002 for the young-, middle- and very-old group, respectively) as well as death at hospital discharge (HR=1.801, 2.036, 2.642, 95% CI 1.454-2.230, 1.638-2.530, 2.047-3.409; all P<0.001).

CONCLUSIONS: The risks of death in the ICU and hospital increase with age among delirious patients.

Key words: Intensive care, Delirium, Aging, Mortality

Wen Gao, Yu-ping Zhang, Jing-fen Jin. Poor outcomes of delirium in the intensive care units are amplified by increasing age: A retrospective cohort study[J]. World Journal of Emergency Medicine, 2021, 12(2): 117-123.

Figures/Tables 3

Figure 1.

Table 1

Characteristics of ICU delirium patients in different age groups

Variables	Total (n=3,931)	Non-aged group (n=1,667)	Young-old group (n=891)	Middle-old group (n=848)	Very-old group (n=525)	χ²/F	P-value
Male, n (%)	2,095 (53.3)	950 (57.0)	505 (56.7)	416 (49.1)	224 (42.7)	43.178	<0.001
Caucasian, n (%)	3,086 (75.9)	1,270 (76.2)	720 (80.8)	671 (79.1)	425 (81.0)	99.837	<0.001
Medical history, n (%)
Dementia	298 (7.6)	15 (0.9)	42 (4.7)	122 (14.4)	119 (22.7)	343.263	<0.001
Hypertension	2,389 (60.8)	804 (48.2)	614 (68.9)	596 (70.3)	375 (71.4)	191.937	<0.001
Diabetes	572 (14.6)	240 (14.4)	160 (18.0)	130 (15.3)	42 (8.0)	26.881	<0.001
Stroke	463 (11.8)	145 (8.7)	108 (12.1)	137 (16.2)	73 (13.9)	33.242	<0.001
Urgent admission, n (%)	1,815 (46.2)	775 (46.5)	385 (43.2)	386 (45.5)	269 (51.2)	8.781	0.032
APACHE IV score, mean±SD	69.20±26.27	64.07±27.50	71.60±25.90	72.53±25.06	76.05±21.39	41.358	<0.001
Ventilation, n (%)	1,942 (49.4)	929 (55.7)	465 (52.2)	370 (43.6)	178 (33.9)	91.199	<0.001
Metabolic acidosis, n (%)	165 (4.2)	81 (4.9)	37 (4.2)	29 (3.4)	18 (3.5)	3.866	0.276
Sepsis, n (%)	440 (11.2)	178 (10.7)	97 (10.9)	93 (11.0)	72 (13.7)	3.930	0.269
ARDS, n (%)	310 (7.9)	125 (7.5)	71 (8.0)	60 (7.1)	54 (10.3)	5.282	0.152
Sedatives, n (%)
Dexmedetomidine	344 (8.8)	181 (10.9)	64 (7.2)	73 (8.6)	26 (5.0)	21.518	<0.001
Propofol	614 (15.6)	303 (18.2)	133 (14.9)	130 (15.3)	48 (9.1)	25.356	<0.001
Benzodiazepines	258 (6.6)	142 (8.5)	53 (5.9)	46 (5.4)	17 (3.2)	22.198	<0.001
Mortality, n (%)
Intensive care unit	325 (8.3)	112 (6.7)^*	95 (10.7)^*	79 (9.3)^*	39 (7.4)^*	13.726	0.003
Hospital	606 (15.4)	173 (10.4)^*	170 (19.1)^*	162 (19.1)^*	101 (19.2)^*	56.347	<0.001
LOS, days, mean±SD
Intensive care unit^a	4.345±2.228	4.700±2.307^*	4.656±2.234^*	4.083±2.158^*	3.350±1.905^*	28.156	<0.001
Hospital^a	8.147±2.137	8.610±2.254^*	8.551±2.104^*	7.870±2.070^*	6.700±1.858^*	16.510	<0.001
Ventilation-free days, mean±SD	4.188±2.193	4.560±2.270^*	4.457±2.213^*	3.873±2.133^*	3.304±1.884^*	22.769	<0.001

Table 1

Table 2

References 48

1	Lim JU, Lee J, Ha JH, Kang HH, Lee SH, Moon HS . Demographic changes in intensive care units in Korea over the last decade and outcomes of elderly patients: a single-center retrospective study. Korean[J] Crit Care Med. 2017; 32(2):164-73.
2	American Psychiatric Association DSM-Task Force Arlington VA US. Diagnostic and statistical manual of mental disorders: DSM-5™( 5th ed.). Codas. 2013; 25(2):191.
3	Sanchez D, Brennan K, Al Sayfe M, Shunker SA, Bogdanoski T, Hedges S , et al. Frailty, delirium and hospital mortality of older adults admitted to intensive care: the Delirium (Deli) in ICU study. Crit Care. 2020; 24(1):609. doi: 10.1186/s13054-020-03318-2 pmid: 33059749
4	Fuchs S, Bode L, Ernst J, Marquetand J, von Känel R, Böttger S. Delirium in elderly patients: prospective prevalence across hospital services. Gen Hosp Psychiatry. 2020; 67:19-25. doi: 10.1016/j.genhosppsych.2020.08.010 pmid: 32911278
5	Li X, Zhang L, Gong F, Ai Y . Incidence and risk factors for delirium in older patients following intensive care unit admission: a prospective observational study.[J] Nurs Res. 2020; 28(4):e101.
6	Ely EW, Shintani A, Truman B, Speroff T, Gordon SM, Harrell FE , et al. Delirium as a predictor of mortality in mechanically ventilated patients in the intensive care unit. JAMA. 2004; 291(14):1753-62. doi: 10.1001/jama.291.14.1753 pmid: 15082703
7	Inouye SK, Westendorp RGJ, Saczynski JS . Delirium in elderly people. Lancet. 2014; 383(9920):911-22. doi: 10.1016/S0140-6736(13)60688-1
8	Hübscher A, Isenmann S . Delirium: concepts, etiology, and clinical management. Fortschr Neurol Psychiatr. 2016; 84(4):233-44. doi: 10.1055/s-0042-104502 pmid: 27100850
9	Rengel KF, Pandharipande PP, Hughes CG . Special considerations for the aging brain and perioperative neurocognitive dysfunction. Anesthesiol Clin. 2019; 37(3):521-36. doi: 10.1016/j.anclin.2019.04.010 pmid: 31337482
10	Zaal IJ, Devlin JW, Peelen LM, Slooter AJC . A systematic review of risk factors for delirium in the ICU. Crit Care Med. 2015; 43(1):40-7. doi: 10.1097/CCM.0000000000000625 pmid: 25251759
11	Falsini G, Grotti S, Porto I, Toccafondi G, Fraticelli A, Angioli P , et al. Long-term prognostic value of delirium in elderly patients with acute cardiac diseases admitted to two cardiac intensive care units: a prospective study (DELIRIUM CORDIS). Eur Heart J Acute Cardiovasc Care. 2018; 7(7):661-70. doi: 10.1177/2048872617695235 pmid: 29064263
12	Serpytis P, Navickas P, Navickas A, Serpytis R, Navickas G, Glaveckaite S . Age- and gender-related peculiarities of patients with delirium in the cardiac intensive care unit. Kardiol Pol. 2017; 75(10):1041-50. doi: 10.5603/KP.a2017.0122 pmid: 28715077
13	Kotfis K, Szylińska A, Listewnik M, Strzelbicka M, Brykczyński M, Rotteret I , et al. Early delirium after cardiac surgery: an analysis of incidence and risk factors in elderly(≥65 years) and very elderly (≥80 years) patients. Clin Interv Aging. 2018; 13:1061-70. doi: 10.2147/CIA.S166909 pmid: 29881262
14	Benchimol EI, Smeeth L, Guttmann A, Harron K, Moher D, Petersen I , et al. The REporting of studies Conducted using Observational Routinely-collected health Data (RECORD) Statement. PLoS Med. 2015; 12(10):e1001885. doi: 10.1371/journal.pmed.1001885 pmid: 26440803
15	Pollard TJ, Johnson AEW, Raffa JD, Celi LA, Mark RG, Badawi O . The eICU collaborative research database, a freely available multi-center database for critical care research. Sci Data. 2018; 5:180178. doi: 10.1038/sdata.2018.178 pmid: 30204154
16	Ely EW, Inouye SK, Bernard GR, Gordon S, Francis J, May L , et al. Delirium in mechanically ventilated patients: validity and reliability of the Confusion Assessment Method for the intensive care unit (CAM-ICU). JAMA. 2001; 286(21):2703-10. doi: 10.1001/jama.286.21.2703 pmid: 11730446
17	Ely EW, Margolin R, Francis J, May L, Truman B, Dittus R , et al. Evaluation of delirium in critically ill patients: validation of the Confusion Assessment Method for the intensive care unit (CAM-ICU). Crit Care Med. 2001; 29(7):1370-9. doi: 10.1097/00003246-200107000-00012 pmid: 11445689
18	Wassenaar A, van den Boogaard M, Schoonhoven L, Donders R, Pickkers P . Delirium prediction in the intensive care unit: comparison of two delirium prediction models. Crit Care. 2018; 22(1):114. doi: 10.1186/s13054-018-2037-6 pmid: 29728150
19	Vittinghoff E, McCulloch CE. Relaxing the rule of ten events per variable in logistic and Cox regression. Am[J] Epidemiol. 2007; 165(6):710-8.
20	Brummel NE, Bell SP, Girard TD, Pandharipande PP, Jackson JC, Morandi A , et al. Frailty and subsequent disability and mortality among patients with critical illness. Am[J] Respir Crit Care Med. 2017; 196(1):64-72. doi: 10.1164/rccm.201605-0939OC
21	Atterton B, Paulino MC, Povoa P, Martin-Loeches I . Sepsis associated delirium. Medicina (Kaunas). 2020; 56(5):240.
22	Ducos G, Mathe O, Balardy L, Lozano S, Murrek M, Ruiz J , et al. Influence of age on decision-making process to limit or withdraw life-sustaining treatment in the intensive care unit—a single center prospective observational study. J frailty aging. 2017; 6(3):148-53. doi: 10.14283/jfa.2017.22 pmid: 28721432
23	Vargas N, Tibullo L, Landi E, Carifi G, Pirone A, Pippo A , et al. Caring for critically ill oldest old patients: a clinical review. Aging Clin Exp Res. 2017; 29(5):833-45. doi: 10.1007/s40520-016-0638-y pmid: 27761759
24	Nabozny MJ, Barnato AE, Rathouz PJ, Havlena JA, Kind AJ, Ehlenbach WJ , et al. Trajectories and prognosis of older patients who have prolonged mechanical ventilation after high-risk surgery. Crit Care Med. 2016; 44(6):1091-7. pmid: 26841105
25	Murman DL . The impact of age on cognition. Semin Hear. 2015; 36(3):111-21. doi: 10.1055/s-0035-1555115 pmid: 27516712
26	Liang JF, Li ZY, Zhang Y, Zhang W, Dong HS, Zhang Y , et al. Analysis of factors affecting the prognosis of ICU patients by multiple logistic regression model: A retrospective cohort study of 1299 patients in 12 consecutive years. Zhonghua Wei Zhong Bing Ji Jiu Yi Xue. 2017; 29(7):602-7. doi: 10.3760/cma.j.issn.2095-4352.2017.07.006 pmid: 28743336
27	Qiu Y, Jiang L, Xi X . Early incidence and prognosis of ICU-acquired weakness in mechanical ventilation patients. Zhonghua Wei Zhong Bing Ji Jiu Yi Xue. 2019; 31(7):821-6. doi: 10.3760/cma.j.issn.2095-4352.2019.07.005 pmid: 31441403
28	Muscedere J, Waters B, Varambally A, Bagshaw SM, Boyd JG, Maslove D , et al. The impact of frailty on intensive care unit outcomes: a systematic review and meta-analysis. Intensive Care Med. 2017; 43(8):1105-22. doi: 10.1007/s00134-017-4867-0 pmid: 28676896
29	Becker S, Müller J, de Heer G, Braune S, Fuhrmann V, Kluge S. Clinical characteristics and outcome of very elderly patients ≥90 years in intensive care: a retrospective observational study. Ann Intensive Care. 2015; 5(1):53. doi: 10.1186/s13613-015-0053-0 pmid: 26055187
30	Fassier T, Duclos A, Abbas-Chorfa F, Couray-Targe S, West TE, Argaud L , et al. Elderly patients hospitalized in the ICU in France: a population-based study using secondary data from the national hospital discharge database.[J] Eval Clin Pract. 2016; 22(3):378-86.
31	Santana-Cabrera L, Lorenzo-Torrent R, Sánchez-Palacios M, Martín Santana JD, Hernández Hernández JR . Influence of age in the duration of the stay and mortality of patients who remain in an intensive care unit for a prolonged time. Rev Clin Esp. 2014; 214(2):74-8. doi: 10.1016/j.rce.2013.09.005
32	Brummel NE, Balas MC, Morandi A, Ferrante LE, Gill TM, Ely EW . Understanding and reducing disability in older adults following critical illness. Crit Care Med. 2015; 43(6):1265-75. doi: 10.1097/CCM.0000000000000924 pmid: 25756418
33	Stelfox HT, Bagshaw SM, Gao S . A retrospective cohort study of age-based differences in the care of hospitalized patients with sudden clinical deterioration.[J] Crit Care. 2015; 30(5):1025-31.
34	Martin-Loeches I, Guia MC, Vallecoccia MS, Suarez D, Ibarz M, Irazabal M , et al. Risk factors for mortality in elderly and very elderly critically ill patients with sepsis: a prospective, observational, multicenter cohort study. Ann Intensive Care. 2019; 9(1):26. doi: 10.1186/s13613-019-0495-x pmid: 30715638
35	Atramont A, Lindecker-Cournil V, Rudant J, Tajahmady A, Drewniak N, Fouard A , et al. Association of age with short-term and long-term mortality among patients discharged from intensive care units in France. JAMA Netw open. 2019; 2(5):e193215. doi: 10.1001/jamanetworkopen.2019.3215 pmid: 31074809
36	Maldonado JR . Acute brain failure: pathophysiology, diagnosis, management, and sequelae of delirium. Crit Care Clin. 2017; 33(3):461-519. doi: 10.1016/j.ccc.2017.03.013 pmid: 28601132
37	Michels M, Michelon C, Damásio D, Vitali AM, Ritter C, Dal-Pizzol F . Biomarker predictors of delirium in acutely ill patients: a systematic review.[J] Geriatr Psychiatry Neurol. 2019; 32(3):119-36.
38	Toth P, Tarantini S, Csiszar A, Ungvari Z . Functional vascular contributions to cognitive impairment and dementia: mechanisms and consequences of cerebral autoregulatory dysfunction, endothelial impairment, and neurovascular uncoupling in aging. Am[J] Physiol Hear Circ Physiol. 2017; 312(1):H1-20.
39	Amarya S, Singh K, Sabharwal M. Ageing process and physiological changes in Gerontology. 2018. Available at https://www.intechopen.com/books/gerontology/ageing-process-and-physiological-changes.
40	Gardner M, Lightman S, Kuh D, Comijs H, Deeg D, Gallacher J , et al. Dysregulation of the hypothalamic pituitary adrenal (HPA) axis and cognitive capability at older ages: individual participant meta-analysis of five cohorts. Sci Rep. 2019; 9(1):4555. doi: 10.1038/s41598-019-40566-x pmid: 30872618
41	Rea IM, Gibson DS, McGilligan V, McNerlan SE, Denis Alexander H, Ross OA. Age and age-related diseases: role of inflammation triggers and cytokines. Front Immunol. 2018; 9:586. doi: 10.3389/fimmu.2018.00586 pmid: 29686666
42	Simons KS, van den Boogaard M, Hendriksen E, Gerretsen J, van der Hoeven JG, Pickkers P , et al. Temporal biomarker profiles and their association with ICU acquired delirium: a cohort study. Crit Care. 2018; 22(1):137. doi: 10.1186/s13054-018-2054-5 pmid: 29801516
43	Khan BA, Perkins AJ, Prasad NK, Shekhar A, Campbell NL, Gao S , et al. Biomarkers of delirium duration and delirium severity in the ICU. Crit Care Med. 2020; 48(3):353-61. doi: 10.1097/CCM.0000000000004139 pmid: 31770149
44	Kuang ZS, Yang YL, Wei W, Wang JL, Long XY, Li KY , et al. Clinical characteristics and prognosis of community-acquired pneumonia in autoimmune disease-induced immunocompromised host: A retrospective observational study. World[J] Emerg Med. 2020; 11(3):145-51. doi: 10.1046/j.1442-2026.1999.00037.x
45	Gong C, Liu X, Tang Y, Huang Y, Fang H, Cheng Y , et al. Analysis of prognosis risk factors of critically ill patients after cardiac surgery: a consecutive 5-year retrospective study. Zhonghua Wei Zhong Bing Ji Jiu Yi Xue. 2019; 31(7):873-7. doi: 10.3760/cma.j.issn.2095-4352.2019.07.015 pmid: 31441413
46	Alonso A, Ebert AD, Kern R, Rapp S, Hennerici MG, Fatar M . Outcome predictors of acute stroke patients in need of intensive care treatment. Cerebrovasc Dis. 2015; 40(1-2):10-7. doi: 10.1159/000430871 pmid: 26022716
47	Kotfis K, Wittebole X, Jaschinski U, Solé-Violán J, Kashyap R, Leone M , et al. A worldwide perspective of sepsis epidemiology and survival according to age: observational data from the ICON audit.[J] Crit Care. 2019; 51:122-32.
48	Reade MC, Finfer S . Sedation and delirium in the intensive care unit. N Engl[J] Med. 2014; 370(5):444-54.

Variables	Cox regression model 1 (ICU mortality)		Cox regression model 2 (Hospital mortality)
Variables	HR (95% CI)	P-value	HR (95% CI)	P-value
Age group
Non-aged	1 (reference)		1 (reference)
Young-old	1.502 (1.138-1.983)	0.004	1.801 (1.454-2.230)	<0.001
Middle-old	1.675 (1.250-2.244)	0.001	2.036 (1.638-2.530)	<0.001
Very-old	1.840 (1.260-2.687)	0.002	2.642 (2.047-3.409)	<0.001
APACHE IV score	1.010 (1.010-1.018)	<0.001	1.013 (1.010-1.016)	<0.001
Ventilation	1.065 (0.810-1.400)	0.654	1.294 (1.070-1.566)	0.008
Sepsis	1.492 (1.115-1.996)	0.007	1.396 (1.122-1.735)	0.003
Dexmedetomidine	0.449 (0.294-0.684)	<0.001	0.652 (0.485-0.877)	0.005

[1]	Ren-qi Yao, Chao Ren, Di Ren, Jin-xiu Li, Ying Li, Xue-yan Liu, Lei Huang, Yong Liu, Mian Peng, Yong-wen Feng, Yong-ming Yao. Development of septic shock and prognostic assessment in critically ill patients with coronavirus disease outside Wuhan, China [J]. World Journal of Emergency Medicine, 2021, 12(4): 293-298.
[2]	Zi-wei Ke, Yue Jiang, Ya-ping Bao, Ye-qin Yang, Xiao-mei Zong, Min Liu, Xiang-yun Guan, Zhong-qiu Lu. Intensivists’ response to hyperoxemia in mechanical ventilation patients: The status quo and related factors [J]. World Journal of Emergency Medicine, 2021, 12(3): 202-206.
[3]	Yu-qing Cui, Xian-fei Ding, Huo-yan Liang, Dong Wang, Xiao-juan Zhang, Li-feng Li, Quan-cheng Kan, Le-xin Wang, Tong-wen Sun. Efficacy and safety of low-dose corticosteroids for acute respiratory distress syndrome: A systematic review and meta-analysis [J]. World Journal of Emergency Medicine, 2021, 12(3): 207-213.
[4]	Hao-tian Chen, Jian-feng Xu, Xiao-xia Huang, Ni-ya Zhou, Yong-kui Wang, Yue Mao. Blood eosinophils and mortality in patients with acute respiratory distress syndrome: A propensity score matching analysis [J]. World Journal of Emergency Medicine, 2021, 12(2): 131-136.
[5]	Wei Guo, Lin-yu Ran, Ji-hong Zhu, Qing-gang Ge, Zhe Du, Fei-long Wang, Wei-bo Gao, Tian-bing Wang. Identifying critically ill patients at risk of death from coronavirus disease [J]. World Journal of Emergency Medicine, 2021, 12(1): 18-23.
[6]	Hai-jiang Zhou, Tian-fei Lan, Shu-bin Guo. Outcome prediction value of National Early Warning Score in septic patients with community-acquired pneumonia in emergency department: A single-center retrospective cohort study [J]. World Journal of Emergency Medicine, 2020, 11(4): 206-215.
[7]	Miao Yuan, Ding-yi Yan, Fang-shi Xu, Yi-di Zhao, Yang Zhou, Long-fei Pan. Effects of sepsis on hippocampal volume and memory function [J]. World Journal of Emergency Medicine, 2020, 11(4): 223-230.
[8]	Rui-xue Sun, Priscilla Song, Joseph Walline, He Wang, Ying-chun Xu, Hua-dong Zhu, Xue-zhong Yu, Jun Xu. Morbidity and mortality risk factors in emergency department patients with Acinetobacter baumannii bacteremia [J]. World Journal of Emergency Medicine, 2020, 11(3): 164-168.
[9]	Shao-hua Liu, Huo-yan Liang, Hong-yi Li, Xian-fei Ding, Tong-wen Sun, Jing Wang. Effect of low high-density lipoprotein levels on mortality of septic patients: A systematic review and meta-analysis of cohort studies [J]. World Journal of Emergency Medicine, 2020, 11(2): 109-116.
[10]	Wei He, Yue-yang You, Kai Sun, Chen Xie, Yue Ming, Li-na Yu, Feng-jiang Zhang, Min Yan. Admission delay is associated with worse surgical outcomes for elderly hip fracture patients: A retrospective observational study [J]. World Journal of Emergency Medicine, 2020, 11(1): 27-32.
[11]	Chang Pan, Xiao-ran Huang, Jiao-jiao Pang, Kai Cheng, Feng Xu, Yu-guo Chen. Trends in mortality of emergency departments patients in China [J]. World Journal of Emergency Medicine, 2019, 10(3): 152-155.
[12]	Suresh Kumar Arumugam, Insolvisagan Mudali, Gustav Strandvik, Ayman El-Menyar, Ammar Al-Hassani, Hassan Al-Thani. Risk factors for ventilator-associated pneumonia in trauma patients: A descriptive analysis [J]. World Journal of Emergency Medicine, 2018, 9(3): 203-210.
[13]	Yong-xia Gao, Yan-bo Song, Ze-juan Gu, Jin-song Zhang, Xu-feng Chen, Hao Sun, Zhen Lu. Video versus direct laryngoscopy on successful first-pass endotracheal intubation in ICU patients [J]. World Journal of Emergency Medicine, 2018, 9(2): 99-104.
[14]	Saeed Mahmood, Omaima Mahmood, Ayman El-Menyar, Mohammad Asim, Hassan Al-Thani. Predisposing factors, clinical assessment, management and outcomes of agitation in the trauma intensive care unit [J]. World Journal of Emergency Medicine, 2018, 9(2): 105-112.
[15]	Yuzeng Shen, Yee Chien Tay, Edward Wee Kwan Teo, Nan Liu, Shao Wei Lam, Marcus Eng Hock Ong. Association between the elderly frequent attender to the emergency department and 30-day mortality: A retrospective study over 10 years [J]. World Journal of Emergency Medicine, 2018, 9(1): 20-25.