Article, Emergency Medicine

Age effects on case fatality rates of injury patients by mechanism

a b s t r a c t

Background: Case fatality from injury increases exponentially with age. The objective of this study is to identify age effects on case fatality of injury patients by injury mechanism.

Methods: This is an observational study using the Emergency Department-based Injury In-depth Surveillance data from 2007 to 2012. Eligibility was all injured patients, excluding those with unknown information for age, disposition after emergency department or admission, or injury mechanism. End point of this study was Inhospital mortality. Injury mechanism was categorized into road transport injury (RTI), fall, collision, cut/pierce, burn, poisoning, and miscella- neous. Case fatality ratio was calculated to evaluate age effects on case fatality by injury mechanism and gender.

Result: Among 927 011 injury patients, a total of 924 755 patients were analyzed. Total case fatality rate was 0.9%, and rates by injury mechanisms were 4.4% in poisoning, 2.1% in RTI, and 0.8% in fall. By age and gender, the highest crude case fatality rate was 19.74% observed in older than 80-year-old men with poisoning. Case fatality ratios in both genders increased by age from 60- to 69-, 70- to 79-, to older than 80-year-old patients; ratios by injury mechanisms were 13.71, 20.76, and 22.29 (male) and 7.21, 11.18, and 13.05 (female) in poisoning; 5.46, 9.30, and 14.13 (male) and 3.90, 7.96, and 12.08 (female) in RTI; 1.22, 1.52, and 2.02 (male) and 1.14, 2.15, and 6.42 (female) in burn.

Conclusions: Case fatality rates of injury increased with age; however, the trends in increase differed by injury mecha- nisms and gender. Strategies for injury prevention and decreasing mortality should consider the age effects on case fa- tality of different injury mechanisms.

(C) 2015

? Funding acknowledgment: The study was funded by the Korea Centers for Disease Control and Prevention (2007-2012).

?? Conflicts of interest: None.

? Author contributions: Drs Park and Ro had full access to all of the data in the study and

take responsibility for the integrity of the data and the accuracy of the data analysis; study concept and design: YJ Park, YS Ro, SD Shin, and KJ Song; acquisition, analysis, or interpreta- tion of data: YJ Park, YS Ro, SD Shin, and KJ Song; drafting of the manuscript: YJ Park, YS Ro, SD Shin, and KJ Song; critical revision of the manuscript for important intellectual content: SD Shin, KJ Song, SC Lee, YJ Kim, JY Kim, KJ Hong, and SC Kim; statistical analysis: YJ Park, YS Ro, and JE Kim; obtained funding: SD Shin, KJ Song, and SC Lee; administrative, technical, or material support: JE Kim and MJ Kim; study supervision: YS Ro, SD Shin, and KJ Song; man- uscript approval: all authors.

?? Disclosures: None.

* Corresponding author at: Laboratory of Emergency Medical Services, Seoul National University Hospital Biomedical Research Institute, 101 Daehak-Ro, Jongno-Gu, Seoul 110-7443, Republic of Korea. Tel.: +82 2 2072 1700; fax: +82 2 744 3967.

E-mail addresses: [email protected] (Y.J. Park), [email protected] (Y.S. Ro), [email protected] (S.D. Shin), [email protected] (K.J. Song), [email protected] (S.C. Lee), [email protected] (Y.J. Kim), [email protected] (J.Y. Kim), [email protected] (K.J. Hong), [email protected] (J.E. Kim), [email protected] (M.J. Kim), [email protected] (S.C. Kim).

Introduction

Injury is a growing Public health problem accounting for 16% of the global Disease burden [1,2]. Approximately 13 000 people die every day due to injuries totaling 8.7% of deaths in the world. Among injury mech- anisms, road transport injury (RTI) was 1 of the top 5 causes for the years of life lost in 2013, and other major causes including drowning, fall, and burn also resulted in high mortality [2]. Deaths due to injuries represent only a small fraction of all patients with injuries, and the total public health burden in the injury pyramid is much greater.

population aging is also an important issue in public health, and the large proportion of elderly in populations continues to grow [3]. The av- erage age of injured patients as well as the proportion of elderly among the injured patients is also increasing year by year [4-6]. Injuries in the elderly are increasing at an incident rate that is 7 times higher than that of younger adults [3]. Previous studies suggest that injured elderly are associated with higher case fatality rate, admission rate, hospital stays, and event-related health care costs [5-10]. The risk of case fatality

http://dx.doi.org/10.1016/j.ajem.2015.12.024

0735-6757/(C) 2015

increased exponentially with age of the injured, and the cutoff age for increased mortality varied from early 40- to 70-year-olds in previous studies [11-13].

Injury mechanism is also a known independent risk factor for case fatality [6,14,15]. Road transport injury and penetrating trauma from gunshot were the most fatal injury mechanisms in all age groups, and fall in the elderly and burn in children were associated with greater physical and Economic burdens in addition to case fatality or disability [2,5,6,14-16]. Fall injuries increased annually by an average of 3% [5], whereas age-standardized mortality from RTI were decreasing in trend [2,6]. The epidemiologic characteristics and clinical course of patients were differentially observed according to injury mechanisms.

As the population continues to mature, identifying the age effects on clinical outcomes by injury mechanism is important for developing bet- ter intervention strategies and dealing with increasing public health burden of injury. Few studies comparing the age effects on case fatality by injury mechanism have been reported, but those few studies mostly reported on the increase in the burden of injury by age only for specific injury mechanisms such as blunt or penetrating trauma. The objectives of this study were to identify the age effects on case fatal- ity rate of injury patients and to compare the trends between different injury mechanisms.

Materials and methods

Study design and setting

This is an observational study using the Emergency Department- Based Injury In-Depth Surveillance (EDIIS) database in Korea. The EDIIS is a nationwide, prospective database of injury patients visiting emergency department (ED) of 20 tertiary academic teaching hospitals, which was sampled geographically by the Korea Centers for Disease Control and Prevention (CDC) for gathering injury-related information for planning national policy for injury prevention. The Ministry of Health and Welfare designated EDs into 3 levels according to the re- sources and functional requirements: level 1 (n = 19) and level 2 (n = 110) EDs have more resources and better facilities for emergency care and must be staffed by emergency physicians 24 hours a day and 365 days a year. The participating EDs for EDIIS consisted of 10 level 1

EDs and 10 level 2 EDs, and the annual number of visits ranged from 30 000 to 90 000. The EDIIS project was organized and financially sup- ported by the Korea CDC.

Data source and collection

The EDIIS was designed based on the core data set of the Internation- al Classification of External Causes of Injuries proposed by the World Health Organization and includes patients’ demographic information, injury-related information, prehospital emergency medical service re- cords, clinical findings, diagnostic assessment and medical treatment in the ED, ED disposition, and patient outcome after admission if the pa- tient was admitted [17].

Primary surveillance and data collection were done by general phy- sicians, and most of the recorded information was supervised and re- vised daily by emergency medicine physicians and trained research coordinators. All research coordinators were trained before joining this project and regularly entered the surveillance data into a Web- based database system of the Korea CDC. The Quality management com- mittee of this project reviewed the data every month and provided feedback to maintain the quality of data.

Study population

The study population was all patients who visited 1 of the 20 EDs between January 2007 and December 2012 with sustained injury, excluding cases with unknown age, injury mechanism, and/or clinical outcomes. Patients visiting the EDs for recurrent complications after injury were not included in this study.

Main outcomes

The study outcome was inhospital mortality, defined as death in ED or during initial admission resulting from the injury event regardless of the duration from injury to death, measured at discharge from ED or hospital.

8 unknown age

924,755 patients included

924,763

926,000

927,003

927,011 patients

1,003 unknown ED disposition

1,237 unknown result of admission

8 unknown injury mechanism

Fig. 1. Study population flow.

Table 1

Demographics findings of study population by injury mechanism

Injury mechanism

Total

RTI Fall Collision Cut/pierce Burn Poisoning Miscellaneous

n

%

n

%

n

%

n

%

n

%

n

%

n

%

n

%

Total 924 755 Age

0-9 244 930

26.5

158 677

16 367

10.3

257 913

85 385

33.1

237 027

79 839

33.7

103 760

20 154

19.4

22 635

8413

37.2

23 876

2361

9.9

120 867

32 411

26.8

10-19 105 547

11.4

20 666

13.0

22 151

8.6

36 814

15.5

10 807

10.4

1766

7.8

1788

7.5

11 555

9.6

20-29 124 670

13.5

27 680

17.4

23 338

9.0

32 445

13.7

18 696

18.0

3089

13.6

3216

13.5

16 206

13.4

30-39 123 500

13.4

25 834

16.3

23 230

9.0

30 357

12.8

19 009

18.3

3228

14.3

3817

16.0

18 025

14.9

40-49 115 942

12.5

23 112

14.6

24 874

9.6

26 794

11.3

16 128

15.5

2803

12.4

4245

17.8

17 986

14.9

50-59 96 040

10.4

20 720

13.1

26 507

10.3

18 200

7.7

11 609

11.2

2066

9.1

3309

13.9

13 629

11.3

60-69 55 835

6.0

13 631

8.6

20 446

7.9

7505

3.2

4867

4.7

767

3.4

2232

9.3

6387

5.3

70-79 39 904

4.3

8641

5.4

20 016

7.8

3619

1.5

1943

1.9

359

1.6

2000

8.4

3326

2.8

>= 80 18 387

Gender

Male 566 072

2.0

61.2

2026

97 875

1.3

61.7

11 966

148 164

4.6

57.4

1454

161 967

0.6

68.3

547

62 859

0.5

60.6

144

11 824

0.6

52.2

908

10 748

3.8

45.0

1342

72 635

1.1

60.1

Mortality

Total 8188

0.9

3409

2.1

1955

0.8

252

0.1

136

0.1

58

0.3

1056

4.4

1322

1.1

ED 4917

0.5

2079

1.3

956

0.4

114

0.0

92

0.1

42

0.2

579

2.4

1055

0.9

Ward/ICU 3271

0.4

1330

0.8

999

0.4

138

0.1

44

0.0

16

0.1

477

2.0

267

0.2

Abbreviations: RTI, road transport injury; ICU, intensive care unit.

Variables and measurements

The main exposure of interest was age of the injured patient on the day of visit to an ED. Age was categorized by decades into 9 groups from 0 to 9 years old to older than 80-year-old group.

Injury mechanism was classified based on International Classifica- tion of External Causes of Injuries into 7 groups of RTI, fall, collision, cut and pierce, burn, poisoning, and miscellaneous. Road transport injury was defined as injuries related to modes of transportation including motor vehicle occupant, pedestrian, bicycle, motorcycle, farming or in- dustrial vehicle, leisure vehicle, and more. Fall was defined as injuries resulting from abrupt descending by force of gravity including falling on the same level, from a height, and on the stairs. Collision was all inju- ries resulting from being struck by blunt forces such as objects, human, and animal and other. Cut and pierce included injuries resulting from cut, piecing, penetration, stabbing, gunshot, needlestick, sting, animal or human bite, and other. Burn was all thermal injuries from fire, smoke, steam, sunlight, hot water or object, and more. Poisoning includ- ed injuries resulting from exposure to chemical or Toxic substances including drug, gas, and other solid or liquid substances. The miscella- neous group included injuries of mechanical force, drowning, asphyxia, hanging, and other mechanisms in which the number of total cases was relatively small. Information about the circumstances of injury episodes

including mechanism of infliction was obtained from patients or their guardians during patient examination by emergency physicians and general physicians.

Statistical analysis

Descriptive analysis was performed to examine the distribution of age, gender, and inhospital mortality between injury mechanisms. To inspect the age effects on case fatality rate by injury mechanisms, the age-specific case fatality rates at 10-year age intervals were calculated and compared. In addition, the adjusted odds ratios (AORs) and 95% confidence intervals (CIs) of age on study end points were calculated for each injury mechanism using logistic regression analysis adjusting for gender, with the 30- to 39-year-old group as reference. Variables were adjusted in the model as potential confounders if they block all backdoor paths from the main exposure to the outcome in directed acy- clic graph (DAG) models (Fig. 2), affect the outcome, and are not medi- ators in a causal pathway [18,19]. To compare the age effects between different injury mechanisms, the case fatality ratios and 95% CIs were calculated as the specific case fatality rate of each injury mechanism, age, and gender group divided by the crude case fatality rate of all inju- ries. Case fatality ratio greater than 1 indicated that there was excess

Table 2

Crude case fatality rate (%) by age, gender, and injury mechanism

Gender Injury mechanism

RTI Fall Collision Cut/pierce Burn Poisoning Miscellaneous

Male

Female

Male

Female

Male

Female

Male

Female

Male

Female

Male

Female

Male

Female

Male

Female

Total Age 0-9

0.98

0.09

0.74

0.07

2.45

0.70

1.66

0.70

0.86

0.05

0.62

0.03

0.13

0.01

0.06

0.01

0.15

0.00

0.10

0.01

0.30

0.02

0.21

0.00

6.54

0.15

2.69

0.19

1.13

0.14

1.04

0.07

10-19

0.33

0.26

1.03

0.75

0.34

0.38

0.02

0.00

0.00

0.00

0.31

0.12

0.00

0.00

0.40

0.25

20-29

0.57

0.42

1.41

0.68

0.64

0.53

0.07

0.03

0.09

0.04

0.07

0.06

1.21

0.63

0.77

0.86

30-39

0.72

0.53

1.72

0.51

0.71

0.73

0.14

0.01

0.15

0.05

0.30

0.13

3.15

1.07

0.73

1.50

40-49

1.15

0.70

2.46

1.13

1.12

0.58

0.27

0.08

0.29

0.16

0.49

0.22

5.41

1.70

1.22

1.38

50-59

1.74

0.90

3.27

1.64

1.64

0.51

0.41

0.10

0.16

0.22

1.09

0.28

7.25

3.38

1.99

1.43

60-69

3.05

1.64

4.83

3.45

2.45

0.81

0.64

0.21

0.48

0.15

1.08

1.01

12.14

6.39

2.93

2.04

70-79

5.25

2.82

8.24

7.05

2.89

1.26

0.62

0.60

1.15

0.78

1.34

1.90

18.38

9.89

6.74

4.79

>= 80

6.32

3.33

12.51

10.70

3.46

2.04

1.68

0.87

1.42

0.89

1.79

5.68

19.74

11.55

10.55

6.17

Table 3

Adjusted odds ratios of age on injury case fatality stratified by injury mechanism

Injury mechanism

Total

RTI

Fall

Collision

Cut/pierce

Burn

Poisoning

Miscellaneous

Age

AOR (95% CI)

AOR (95% CI)

AOR (95% CI)

AOR (95% CI)

AOR (95% CI)

AOR (95% CI)

AOR (95% CI)

AOR (95% CI)

0-9

0.13 (0.11-0.15)

0.55 (0.44-0.68)

0.06 (0.04-0.09)

0.11 (0.05-0.23)

0.06 (0.01-0.45)

0.11 (0.08-0.16)

10-19

0.46 (0.40-0.52)

0.72 (0.61-0.86)

0.47 (0.36-0.61)

0.18 (0.08-0.41)

0.03a (0.00-0.22)

1.05 (0.31-3.57)

0.05a (0.02-0.13)

0.34 (0.24-0.48)

20-29

0.80 (0.72-0.89)

0.89 (0.76-1.05)

0.86 (0.69-1.08)

0.58 (0.33-1.04)

0.60 (0.29-1.21)

0.30 (0.06-1.44)

0.45 (0.29-0.70)

0.82 (0.65-1.03)

30-39

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

40-49

1.53 (1.40-1.68)

1.56 (1.35-1.80)

1.29 (1.06-1.58)

2.13 (1.37-3.32)

2.19 (1.29-3.72)

1.65 (0.63-4.33)

1.70 (1.28-2.28)

1.28 (1.05-1.56)

50-59

2.23 (2.04-2.43)

2.12 (1.85-2.44)

1.67 (1.38-2.02)

3.22 (2.07-5.01)

1.65 (0.90-3.02)

3.14 (1.27-7.79)

2.69 (2.03-3.55)

1.83 (1.50-2.22)

60-69

3.97 (3.63-4.33)

3.56 (3.10-4.09)

2.49 (2.07-3.01)

5.15 (3.17-8.38)

3.20 (1.69-6.07)

4.85 (1.75-13.42)

4.88 (3.71-6.42)

2.66 (2.15-3.29)

70-79

6.91 (6.34-7.53)

6.73 (5.87-7.70)

3.16 (2.63-3.80)

7.35 (4.23-12.78)

9.66a (5.40-17.31)

11.25a (4.41-28.70)

7.97 (6.11-10.40)

6.21 (5.04-7.64)

>= 80

8.21 (7.43-9.08)

10.90 (9.15-12.99)

4.43 (3.65-5.38)

16.03 (8.77-29.32)

9.15 (6.79-12.32)

8.78 (6.85-11.26)

Adjusted odds ratio was calculated adjusting for gender and 30- to 39-year-old group as a reference for each injury mechanism.

a Two age groups were combined due to the small number of deaths.

mortality in the specific group compared to all injured patients. All statistical analysis was performed using SAS software, version 9.4 (SAS Institute, Inc, Cary, NC). P values were based on a 2-sided significance level of .05.

Ethics statements

The study was reviewed and approved by the Institutional Review Board of Seoul National University Hospital (IRB no. 1103-152-357). In- formed consent was waived, and patient information was anonymized before analysis.

Results

Among 927 011 injured patients, 924 755 patients (99.8%) were analyzed excluding those with unknown age (n = 8), unknown ED disposition (n = 1003), unknown hospital outcome (n = 1237), and unknown mechanism of injury (n = 8) (Fig. 1).

Table 1 shows patient demographics by injury mechanisms. Fall, poisoning, and RTI were Major injury mechanisms in the elderly group, whereas fall, collision, and burn were frequent in the children

group. Total case fatality rate was 0.9%, and crude case fatality rates by injury mechanism were 4.4% in poisoning, 2.1% in RTI, and 0.8% in fall.

Crude case fatality rates by age and gender varied from 0.07% to 6.32% for all injury patients, and the highest crude case fatality rate was 19.74% observed in older than 80-year-old man with poisoning. The crude case fatality rate tended to increase according to patients’ age for all injury mechanisms (Table 2).

To evaluate the age effect in each injury mechanism, the AORs (95% CI) of case fatality in each age group compared to 30- to 39-year-old group with same mechanism are reported in Table 3. The AORs (95% CI) of case fatality in 70- to 79-year-old group and older than 80-year- old group compared to 30- to 39-year-old group were 7.35 (4.23- 12.78) and 16.03 (8.77-29.32) in collision, 6.73 (5.87-7.70) and 10.90 (9.15-12.99) in RTI, and 7.97 (6.11-10.40) and 9.15 (6.79-12.32) in poi-

soning, respectively. There were dose-response relationships of age ef- fects on case fatality for all injuries and by specific injury mechanisms. To evaluate the effect of injury mechanism, a multivariable logistic regression model was conducted adjusting for age and gender. The AORs (95% CI) of case fatality compared to fall were 5.40 (4.99-5.83) in poisoning, 2.93 (2.76-3.10) in RTI, 1.84 (1.71-1.98) in miscellaneous,

0.55 (0.42-0.71) in burn, 0.23 (0.19-0.27) in cut and pierce, and 0.22

(0.20-0.25) in collision.

Table 4

Case fatality ratio and 95% CI by age, gender, and injury mechanism

Injury mechanism

Total

RTI

Fall

Collision

Cut/pierce

Burn

Poisoning

Miscellaneous

CFR (95% CI)

CFR (95% CI)

CFR (95% CI)

CFR (95% CI)

CFR (95% CI)

CFR (95% CI)

CFR (95% CI)

CFR (95% CI)

Male

0-9

0.10 (0.08-0.12)

0.79 (0.61-0.99)

0.06 (0.04-0.08)

0.01 (0.00-0.03)

0.00 (0.00-0.03)

0.02 (0.00-0.13)

0.17 (0.02-0.62)

0.16 (0.10-0.24)

10-19

0.37 (0.32-0.42)

1.17 (0.99-1.37)

0.39 (0.29-0.50)

0.03 (0.01-0.06)

0.00 (0.00-0.06)

0.35 (0.07-1.04)

0.00 (0.00-0.66)

0.45 (0.30-0.66)

20-29

0.65 (0.59-0.71)

1.59 (1.39-1.81)

0.72 (0.58-0.89)

0.08 (0.04-0.13)

0.10 (0.04-0.18)

0.08 (0.00-0.44)

1.36 (0.74-2.29)

0.87 (0.68-1.10)

30-39

0.81 (0.74-0.88)

1.94 (1.72-2.19)

0.80 (0.66-0.97)

0.16 (0.10-0.22)

0.16 (0.10-0.26)

0.34 (0.11-0.78)

3.56 (2.62-4.74)

0.83 (0.66-1.02)

40-49

1.30 (1.21-1.40)

2.78 (2.48-3.09)

1.26 (1.08-1.47)

0.30 (0.22-0.40)

0.33 (0.22-0.47)

0.55 (0.22-1.13)

6.11 (4.92-7.49)

1.38 (1.17-1.62)

50-59

1.97 (1.84-2.10)

3.70 (3.33-4.10)

1.85 (1.62-2.11)

0.47 (0.35-0.62)

0.18 (0.09-0.32)

1.23 (0.61-2.20)

8.19 (6.80-9.77)

2.25 (1.93-2.61)

60-69

3.44 (3.21-3.68)

5.46 (4.92-6.05)

2.77 (2.43-3.15)

0.72 (0.49-1.03)

0.55 (0.30-0.92)

1.22 (0.33-3.14)

13.71 (11.62-16.07)

3.31 (2.73-3.98)

70-79

5.93 (5.54-6.34)

9.30 (8.41-10.27)

3.27 (2.85-3.73)

0.70 (0.35-1.25)

1.29 (0.67-2.26)

1.52 (0.18-5.48)

20.76 (17.90-23.95)

7.61 (6.27-9.17)

>= 80

7.13 (6.44-7.89)

14.13 (11.82-16.77)

3.91 (3.24-4.67)

1.89 (0.87-3.60)

1.61 (0.33-4.69)

2.02 (0.05-11.24)

22.29 (17.52-27.97)

11.91 (8.99-15.48)

Female

0-9

0.08 (0.06-0.11)

0.79 (0.57-1.07)

0.04 (0.02-0.07)

0.01 (0.00-0.03)

0.01 (0.00-0.08)

0.00 (0.00-0.11)

0.22 (0.03-0.79)

0.08 (0.04-0.15)

10-19

0.30 (0.23-0.37)

0.85 (0.61-1.15)

0.43 (0.27-0.63)

0.00 (0.00-0.05)

0.00 (0.00-0.11)

0.14 (0.00-0.78)

0.00 (0.00-0.36)

0.28 (0.14-0.49)

20-29

0.48 (0.41-0.55)

0.76 (0.60-0.96)

0.60 (0.45-0.79)

0.04 (0.01-0.11)

0.04 (0.01-0.12)

0.07 (0.00-0.38)

0.71 (0.38-1.22)

0.97 (0.74-1.25)

30-39

0.59 (0.52-0.68)

0.58 (0.43-0.76)

0.83 (0.63-1.06)

0.01 (0.00-0.07)

0.06 (0.02-0.16)

0.15 (0.02-0.53)

1.21 (0.78-1.79)

1.70 (1.37-2.09)

40-49

0.79 (0.70-0.89)

1.28 (1.04-1.55)

0.66 (0.49-0.86)

0.09 (0.04-0.19)

0.18 (0.09-0.34)

0.25 (0.05-0.73)

1.92 (1.39-2.59)

1.56 (1.23-1.95)

50-59

1.02 (0.91-1.13)

1.85 (1.56-2.18)

0.58 (0.44-0.75)

0.12 (0.04-0.25)

0.24 (0.12-0.45)

0.32 (0.07-0.94)

3.82 (2.86-4.98)

1.62 (1.26-2.06)

60-69

1.85 (1.67-2.04)

3.90 (3.37-4.49)

0.91 (0.73-1.13)

0.24 (0.09-0.52)

0.17 (0.04-0.50)

1.14 (0.31-2.91)

7.21 (5.51-9.28)

2.31 (1.72-3.04)

70-79

3.18 (2.92-3.46)

7.96 (7.00-9.02)

1.43 (1.21-1.67)

0.67 (0.34-1.21)

0.88 (0.36-1.82)

2.15 (0.59-5.51)

11.18 (9.02-13.69)

5.41 (4.28-6.75)

>= 80

3.77 (3.40-4.16)

12.08 (9.85-14.67)

2.31 (1.97-2.69)

0.99 (0.43-1.94)

1.01 (0.21-2.95)

6.42 (2.08-14.98)

13.05 (9.97-16.78)

6.96 (5.16-9.19)

Abbreviation: CFR, case fatality ratio.

Inter-facility transfer

Case-fatality

Injury mechanism

Hospital treatment

prehospital management

Injury severity

Gender

Age

Fig. 2. Directed acyclic graph model.

To compare the age effect between injury mechanisms, the case fatality ratios by injury mechanism, age, and gender are presented in Table 4. Case fatality ratios (95% CI) of older than 80-year-old male group were 22.29 (17.52-27.97) in poisoning, 14.13 (11.82-16.77) in

RTI, 11.91 (8.99-15.48) in miscellaneous, and 2.02 (0.05-11.24) in burn, whereas in older than 80-year-old female group, the ratios were

13.05 (9.97-16.78) in poisoning, 12.08 (9.85-13.67) in RTI, 6.96 (5.16-

9.19) in miscellaneous, and 6.42 (2.08-14.98) in burn. Case fatality ra- tios in 70- to 79-year-old male were 20.76 (17.90-23.95) in poisoning,

9.30 (8.41-10.27) in RTI, 7.61 (6.27-9.17) in miscellaneous, and 1.52 (0.18-5.48) in burn; in 70- to 79-year-old female, the ratios were

11.18 (9.02-13.69) in poisoning, 7.96 (7.00-9.02) in RTI, 5.41 (4.28-

6.75) in miscellaneous, and 2.15 (0.59-5.51) in burn. The highest case fatality ratio was 22.29 in male older than 80 years with poisoning, which means that there were 22.29 times excess mortality cases than the Expected mortality cases using crude case fatality rate. There were different trends of age effects on case fatality ratios according injury mechanisms. The case fatality ratios increased relatively rapidly by age in patients with poisoning, RTI, miscellaneous injuries, burn (only fe- male), and fall, whereas those with collision, cut and pierce, and burn (male) observed relatively slow increase or no increase at all.

Discussion

This study evaluated age effects on case fatality rate of injured pa- tients and compared the age effects between injury mechanisms using a nationwide and prospective registry in Korea. There were dose- response relationships observed between age and case fatality in specif- ic injury mechanisms. Older patients were more likely to die of injuries compared with younger patients with the same injury mechanism. When the age effects were compared between mechanisms of injury, however, the case fatality ratios only increased with age in injuries of poisoning, RTI, miscellaneous causes, burn (only female), and fall. It means older patients with the aforementioned injury mechanisms ob- served excess mortality than the expected mortality based on the over- all case fatality rate of all injured patients. These findings suggest that age is a risk factor for higher case fatality from injury, and the age- related case fatality ratios increase rapidly in some injury mechanisms, highlighting the need to develop better strategies for managing the complex care needs of these patients.

Age is an independent risk factor for the case fatality of injury pa- tients [7-9,11,20]. The cutoff age for the increased injury case fatality was suggested in previous studies; the age-related change in outcomes may begin at various ages including as early as age 40 [13], mid-50 [8,11], or older than 65 [12,21]. In this study, the effect measure (AOR) showed statistically significant increase in case fatality by age. Com- pared to 30 to 39 years old with the same injury mechanism, patients older than 40 years were more likely to die of injuries of all mechanisms. Furthermore, the increasing trend in mortality was more pronounced in 70- to 79-year-old group and older; for example, the AORs for 70- to 79-

year-old and older than 80-year-old patients with RTI were 6.73 (5.87- 7.70) and 10.90 (9.15-12.99), respectively. These findings may be attributed to most of the elderly having 1 or more chronic condi- tions including cardiovascular disease [22], thus leaving them more vulnerable to Hemodynamic compromise and acute stressful conditions. In addition, dysregulation of posttraumatic inflammatory responses also contributes to the high mortality of the elderly [23].

In this study, fall was the most common injury mechanism in the el- derly, and its crude case fatality rate was 0.9%. A previous study showed the increasing incidence and hospital admission of fall-related injuries, and the increment of incidence among the elderly was 2-fold greater than in young adults [5]. In this study, fall was the third most fatal injury mechanism after poisoning and RTI. Previous studies reported that fall- related severe injuries and case fatality accounted for a half of all severe injury hospitalization [5,6,24]. Exercises such as tai-chi and yoga for the elderly would enhance postural control and reduce the incidence and severity of fall injury [25].

Comparing the age effects between mechanisms of injury, the case fatality ratios of poisoning and RTI rapidly increased by age. Poisoning was associated with a high incidence in the elderly and was the most fatal injury mechanism (case fatality rate, 4.4%) in this study. The highest case fatality ratio (22.29) was shown in male older than 80 years with poisoning, indicating a significant number of excess mor- tality cases in this group. In Korea, 4.4% of all out-of-hospital cardiac ar- rests with noncardiac etiology were caused by poisoning, and the elderly patients were more likely to us insecticides or herbicides rather than drugs [26]. The elderly patients may, therefore, be injured from more fatal substances, attributing to a Rapid increase in case fatality ratio by age. Public health policies such as registration and ban on the sales and production of toxic materials would reduce the incidence of deliberate poisoning [27,28]. Road transport injury was the second most fatal injury mechanism in this study and was also the second most common injury mechanism in the elderly. Road transport injury is 1 of top 5 causes of all mortality globally, and its absolute incidence is increasing as the number of vehicles increases [2,6]. Road transport injury is predicted to have higher case fatality and more functional im- pairment compared to other blunt trauma [15]. The elderly and children are defined as vulnerable road users, and they are more likely to use the road as pedestrians or bicycle users who are at a higher risk for severe injury. As such, education, enforcement, and engineering are the highly effective Prevention strategies for RTI.

The case fatality ratios of cut and pierce injuries were relatively low in all age groups. In Korea, guns are strongly prohibited by law. There was some evidence that the case fatality of penetrating trauma was higher than that of blunt trauma in some countries where possession of firearm is approved [11]. However, gunshot wounds are extremely rare in Korea, and most cut and pierce injuries would be relatively less life threatening. Therefore, case fatality from cut and pierce would be lower compared to other countries.

Injuries are a global health burden, and aging is also an important issue in public health. The elderly population is predicted to expand an- nually, and the proportion of the elderly will reach 20% of the global population in 2050. The magnitude of increase in case fatality ratio of in- jury by age was large in the elderly while small in younger patients. These findings suggest the need for developing better strategies for managing the complex care needs of the elderly patients including inva- sive monitoring and aggressive triage approach to reduce undertriage [5,8]. In addition, careful consideration of the interaction between injury mechanism and age would help enhance the management and out- comes of injury.

Study limitations

The study has several limitations. First, we analyzed injured patients visiting the 20 EDs participating in the EDIIS. These EDs perform at rel- atively higher Service levels (level 1 or 2), and injured patients visiting EDs of lower level were not included in this study. This selection bias can cause underestimation or overestimation of age effect on the case fatality of injured patients. Second, there were many factors associated with case fatality of injured patients including injury severity, prehospital management, and hospital treatment (Fig. 2). In this study, we assumed that those factors were all mediators of age effects as they lie on the long causal pathway leading from patients’ age to fa- tality. Potential confounders were adjusted in the main analysis if they block all backdoor paths from the main exposure to the outcome, affect the outcome, and are not mediators in DAG model [18,19]. An undirect- ed path between the exposure variable and the outcome variable was termed a backdoor path if it starts with an arrow pointing into the expo- sure variable. Assuming that injury mechanism was an effect modifier, we conducted the main analysis stratified by injury mechanism. Injury mechanism was a collider in this DAG model, and therefore, a new path between age and gender was opened up by conditioning on the collider. Using the rules of DAG models, we selected gender as a mini- mally sufficient conditioning set to estimate the unbiased effect of age. However, there is a possibility that there is some backdoor path that can bias the age effects on case fatality. Third, this was an observational study, not an intervention trial. There may be significant potential biases that were not controlled. Fourth, we measured inhospital mortality of injured patients visiting the ED and did not identify mortality caused di- rectly by the injury event. Lastly, long-term mortality resulting from the injury event was not included.

Conclusions

The risk of case fatality for injured patients increased rapidly by age for each mechanism of injury. Comparing age effects between mecha- nisms of injury, poisoning, RTI, burn (only female), and fall resulted in rapid increments in the case fatality ratio by age. These mechanisms of injury were associated with excess mortality cases in the elderly compared to all injured patients. These epidemiologic characteristics should be considered in developing strategies for injury prevention and decreasing mortality and disability from injury.

Acknowledgment

This study was financially supported by Korea Centers for Disease Control and Prevention of the Republic of Korea Government (2007-2012).

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