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Abstract
Introduction: We retrospectively investigated prognostic factors for severe abdominal trauma patients evacuated by a physician-staffed helicopter emergency medical service (HEMS) and ground ambulance using the Japan Trauma Data Bank (JTDB). Methods: The study period was from January 2004 to May 2019. The subjects were divided into two groups, according to the type of outcome: the Mortality group, which included patients who ultimately died, and the Survival group, which included patients who obtained a survival outcome. Results: There were 2457 in the Mortality group and 11,326 in the Survival group. When variables that showed statistical significance in the univariate analysis were included in a multivariate analysis, the following variables were identified as significant positive predictors of a fatal outcome: evacuation from the scene, blunt injury, injury severity score, and age; significant negative predictors of a fatal outcome were transportation by the HEMS and revised trauma score. Conclusions: The present study described the usefulness of the HEMS for severe abdominal trauma patients in comparison with ground ambulance transportation using the JTDB.
Keywords: Helicopter ambulance, survival, trauma
How to cite this article: Introduction 
The Ministry of Health, Labor, and Welfare established a physician-staffed helicopter emergency medical service (HEMS) in 2001. The HEMS operates during daytime. The main purpose of the HEMS is early medical intervention rather than early transportation to a hospital for various patients, including those with intrinsic and extrinsic disease.[1] As of January 2021, 53 helicopters had been deployed in 44 prefectures across Japan. In 2019, 23,922 patients were transported by the HEMS.
The Japan Trauma Data Bank (JTDB) was established in 2003 and was authorized by the Japanese Association for the Surgery of Trauma (Trauma Surgery Committee) as well as the Japanese Association for Acute Medicine (Committee for Clinical Care Evaluation). In 2016, 256 major emergency medical institutions across Japan were included in the JTDB.[2],[3],[4] Most of the registered institutions are acute critical care and trauma centers including hospitals with a physician-staffed helicopter base. An analysis using the JTDB revealed that, among patients with major trauma in Japan, transport by helicopter with a physician was associated with an improved survival to hospital discharge compared to transport by ground emergency services.[4] However, what kinds of major trauma are typically useful when patients are transported by the HEMS has not yet been investigated, except for in cases of severe chest trauma.[5] Compared with emergency medical technicians in ground ambulances in Japan, physicians in the HEMS can perform ultrasound to evaluate abdominal injury, use drugs, and perform transfusion and tracheal intubation before cardiac arrest, even in a prehospital setting.[5],[6] Accordingly, we hypothesized that the HEMS might positively influence the outcomes of patients with severe abdominal injury compared with a ground ambulance.
We therefore retrospectively investigated the prognostic factors of severe abdominal trauma patients evacuated by the HEMS and ground ambulance using the JTDB.
Methods The protocol of this retrospective study was approved by our institutional review board, and the examinations were conducted according to the standards of good clinical practice and the Declaration of Helsinki. The approval number was 401.
This study was a retrospective analysis of the JTDB database. The study period was from January 2004 to May 2019. After the application of the exclusion criteria, all severe abdominal trauma patients transported by the HEMS and ground ambulance whose data were registered in the JTDB database were included in the present study. The definition of severe abdominal traumatized patients was an abbreviated injury scale (AIS) of 3–5 because an AIS of 1 or 2 is a minor injury while a 6 is instantaneous deadly trauma.[7] The exclusion criteria were as follows: age, sex, mechanism of injury (penetrating or blunt), origin of transportation (evacuation from scene or inter-hospital transportation), injury severity score (ISS), revised trauma score (RTS) on arrival, or outcome were unknown.[7],[8] The subjects' age, sex, treatments (oxygen, drip infusion, others; including performing ultrasound, using drugs, transfusion, tracheal intubation, thoracostomy, thoracotomy and drainage for cardiac tamponade), prehospital and in-hospital vital signs (systolic blood pressure, heart rate, respiratory rate, Japan Coma Scale [JCS]), RTS on arrival, abdominal AIS, ISS, and the outcome were investigated.[9] The subjects were divided into two groups: the Mortality group, which included patients who ultimately died, and the Survival group, which included patients who obtained a survival outcome. The variables were compared between the two groups.
We also performed a second analysis. The subjects were divided into two groups: The HEMS group included cases transported by the HEMS, while the Ambulance group included cases transported by ground ambulance. The changes in the vital signs between the prehospital and in-hospital settings and the medical treatments administered during transportation in the HEMS group and Ambulance group were also analyzed.
All statistical analyses were performed using the JMP 13.0 software program (SAS Japan Incorporation, Tokyo, Japan). The data were analyzed using a paired Student's t-test for changes in vital signs between prehospital and in-hospital and a nonpaired Student's t-test or the Chi-squared test for comparisons between the two groups. P < 0.01 was considered to indicate a statistically significant difference. All of the data are presented as the mean ± standard deviation or median with the interquartile range. Variables that showed statistical significance (P < 0.01) in a univariate analysis were included in a multivariate analysis to evaluate independent predictors of the survival.
Results During the investigation period, a total of 353,582 patients were registered in the JTDB. Among them, there were 36,797 cases of thoracic trauma, 18,161 cases of severe thoracic trauma, and 14,874 cases of severe thoracic trauma transported by the HEMS or a ground ambulance. After excluding 1091 patients with missing data on the age, sex, mechanism of injury, origin of transportation, ISS, RTS on arrival, or outcome, a total of 13,783 patients were enrolled as subjects, including 2457 in the Mortality group and 11,326 in the Survival group.
The results of the analysis of the two groups are shown in [Table 1]. The average age, ratio of blunt injury, ratio of evacuation from scene, average abdominal AIS, and ratio of helicopter transportation were significantly greater in the Mortality group than in the Survival group, while the average RTS was significantly smaller in the Mortality group than in the Survival group.
Table 1: Background characteristics of subjects in the mortality and survival groups[Table 2] shows the changes in the vital signs between prehospital and in-hospital settings in the Heli and Ambulance groups. The average systolic blood pressure and respiratory rate in the Heli group were significantly greater in the prehospital setting than in the in-hospital setting. The average JCS in the Heli group was significantly smaller in the prehospital setting than in the in-hospital setting (deteriorating unconsciousness). The average systolic blood pressure, respiratory rate, and JCS in the Ambulance group were significantly greater in the prehospital setting than in the in-hospital setting (improving unconsciousness).
Table 2: Vital changes between the prehospital and in-hospital setting in the helicopter group (n=1861) and in the ambulance group (n=11,922)[Table 3] shows the medical treatments administered during transportation between the Heli and Ambulance groups. The ratio of drip infusion was significantly higher in the Heli group than in the Ambulance group. The ratio of other medical interventions was also higher in the Heli group than in the Ambulance group but not to a significant degree.
When variables that showed statistical significance in the univariate analysis in [Table 1] were included in a multivariate analysis, the following variables were identified as significant positive predictors of a fatal outcome: evacuation from the scene, blunt injury, ISS, and age; significant negative predictors of a fatal outcome included transportation by the HEMS and the RTS [Table 4].
Table 4: Results of a multivariate nominal logistic regression analysis for the mortalityThe present findings showed a high frequency of HEMS in the Mortality group, although transportation via HEMS was a negative predictor of a fatal outcome. We therefore performed a further analysis between the HEMS and Ambulance groups concerning the age, ISS and RTS, which are well-known prognostic factors.[8] As a result, the age and ISS in the Heli group were shown to be significantly greater than those in the Ambulance group (52.7 ± 22.7 vs. 47.1 ± 22.4-year-old, <0.0001; 27.9 ± 14.2 vs. 24.9 ± 14.5, <0.0001 respectively). In addition, the RTS of the HEMS group was significantly smaller than that in the Ambulance group (6.41 ± 2.17 vs. 6.66 ± 2.06, <0.0001). After a propensity score-matched analysis, there were no significant differences in the age, ISS, or RTS between the two groups. However, the mortality ratio was significantly smaller in the HEMS group than in the Ambulance group [Table 5].
Discussion This is the first report to describe the usefulness of the HEMS for severe abdominal trauma patients using the JTDB. Based on the results, the ISS and age were identified as positive prognostic factors, and the RTS and transportation by the HEMS were identified as negative prognostic factors for mortality. Among these, the three strongest factors (RTS, ISS, age) are well-known prognostic factors that are included in the Trauma and ISS (TRISS), which is used to predict the survival of trauma patients.[8] Accordingly, the standard predictor of the TRISS might also be useful for predicting the viability of severe abdominal trauma patients.
The present study demonstrated the usefulness of the HEMS for managing severe abdominal trauma patients. As mentioned in the introduction, a physician can perform special medical treatments that are impossible for emergency medical technicians to administer. The higher ratio (not statistically significant) of “other medical interventions” in the Heli group than in the Ambulance group suggested such medical treatments. Concerning changes in vital signs between the two groups, consciousness deterioration after arriving at the hospital might suggest that the patients were treated with sedatives or pain killers for tracheal intubation or surgical intervention. Such early medical intervention performed by physicians in the prehospital setting might result in a survival outcome. Unfortunately, we were unable to determine whether deterioration of consciousness was based on the deterioration of trauma itself or the result of medical intervention. As a result, we were unable to indicate the usefulness of the HEMS among subjects who showed deterioration of consciousness.
The present study showed that evacuation from the scene was more closely associated with mortality than interhospital transportation. In general, in the most severely injured and time-sensitive cases, bypassing the nearest hospital for trauma care can substantially improve the survival outcomes.[10],[11],[12] However, the ISS of the patients who were evacuated from the scene in the present study was significantly greater and the RTS smaller than those in patients with interhospital transportation. These findings suggest that the severity of trauma in patients evacuated from the scene was greater than that in patients who received interhospital transportation in the present study. This severity of trauma may also explain the poor outcome of the patients who were evacuated from the scene.
We also observed that blunt injury was more strongly associated with mortality than penetrating injury. However, the comparison of the outcomes of blunt and penetrating abdominal injury differs among countries.[13],[14],[15] This may be due to the kinds of penetrating injury (with consequently different outcomes) differing among countries. For example, both stab wounds and gunshot wounds were considered “penetrating injury.” However, the survival outcome of stab wounds is generally higher than that of gunshot wounds.[16],[17] In Japan, the use of guns is strictly prohibited, and there are few gunshot wounds.[18] Accordingly, even though the JTDB did not describe the details of penetrating injury, most penetrating wounds in the present study are considered stab wounds. In other countries, however, gunshot wounds are more common than in Japan.[19],[20] These differing backgrounds among countries may contribute to differences in the outcome of penetrating injuries.
The present study was associated with some limitations. First, the study failed to describe in detail the contents of the medical intervention performed during transportation. Because the JTDB was built for the analysis of the activity of emergency medical technicians in a prehospital setting, details concerning the medical intervention performed by physicians in a prehospital setting were not recorded in the JTDB. Second, we did not investigate the time or distance from the scene to the hospital, so whether or not the severe abdominal trauma patients located close to the hospital should be transported by HEMS is unclear. Thus, prospective studies are needed to corroborate or expand on our findings.
Conclusions The present study described the usefulness of the HEMS for severe abdominal trauma patients in comparison with ground ambulance transportation using the JTDB.
Research quality and ethics statement
This study was approved by the Institutional Review Board (Juntendo Shizuoka Hospital IRB# 401). The authors followed applicable EQUATOR Network (http://www.equator-network.org/) guidelines during the conduct of this research project.
Acknowledgment
This manuscript received financial support from the Ministry of Education, Culture, Sports, Science and Technology (MEXT)-Supported Program for the Strategic Research Foundation at Private Universities, 2015-2019 concerning (The constitution of total researching system for comprehensive disaster, medical management, corresponding to wide-scale disaster).
Financial support and sponsorship
This work was supported in part by a Grant-in-Aid for Special Research in Subsidies for ordinary expenses of private schools from The Promotion and Mutual Aid Corporation for Private Schools of Japan.
Conflicts of interest
There are no conflicts of interest.
References 
Correspondence Address:
Youichi Yanagawa
1129 Nagaoka, Izunokuni City, Shizuoka 410-2295
Japan
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/jets.jets_96_21
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