1. Introduction
Traffic accidents result in approximately 1.35 million deaths and more than 50 million injuries worldwide each year [1]. Traffic accidents are the leading cause of death in people aged 5 to 29 years and the second most common mechanism of injury in the elderly [1, 2]. These accidents are the main cause of disability, in the long term, so for every death, three severe injuries occur [3], and two injured people become permanently disabled [4]. According to Forensic Medicine Organization, in 2018, 17183 deaths and 367451 injuries were registered in the Iran due to traffic accidents [5]. Care and treatment in traffic accidents are time-dependent; a few minutes delay in providing medical services can mean the difference between life and death [6, 7]. Most deaths due to traffic accidents occur in the first hour after the accident [6].
Effective prehospital emergency care reduces the risk of death by 25% [8]. Air emergency medical service is a vital component of this care system [4]. The main task of the air emergency is to provide primary care at the scene of the accident and to transfer the patients to the hospitalquickly [9]. Today, air emergencies to transport patients are common in most developed countries [10]. Air emergencies can extend geographical access to a hospital [11]. One of the limitations of air emergency over ground emergency is the safety issue. The crash of emergency helicopters over the past few years has raised concerns about air emergency safety [12]. The next limitation of air emergency is its higher cost. The use of air emergencies in the United States shows a cost increase of $ 200-240 million compared to ground emergencies [13].
Studies have been conducted on the outcome of air and ground emergency transport patients. Some studies have confirmed an increased survival rate in air emergencies [7, 14, 15, 16, 17]. Other studies have shown this increase in specific groups [18, 19, 20]. Another group of studies did not report a change in outcome [11, 21, 22]. These different results may be due to the type of study, statistical methods, differences in prehospital emergency systems in different countries, patients studied, the educational level of caregivers, limited sample size, and insufficient control of confounding variables. So, it is difficult to compare and generalize results [12, 19, 23]. Air emergency in Qom Province was established in August 2014 [24]. Qom is the second smallest province in Iran. This province has the highest urbanization rate and the shortest road routes in the country. But, it is the transportation route from and to 17 provinces of the country that increases the probability of traffic accidents [25, 26]. Therefore, the present study was designed and conducted to investigate the outcome of air and ground emergency patients in traffic accidents in Qom Province from 2015 to 2019.

2. Materials and Methods
In this retrospective descriptive-analytical study, we examined by numerical method all road traffic accident patients transferred to Shahid Beheshti Hospital in Qom by ground or air from March 21, 2015, to March 20, 2019. Prehospital exclusion criteria included treatment at the accident scene without transferring to a hospital, against medical advice with transfer to a hospital, death at the scene, cardiopulmonary resuscitation during transfer, burns, intra-city accidents, mission time from 20:00 to 6:00, and prehospital record deficiencies. Hospital exclusion criteria also included hospital death, against medical advice to discontinue treatment, transfer to another hospital to continue treatment, escape from the hospital, and deficiencies in the hospital record. A researcher-made checklist whose content validity was approved by faculty members was used to collect study data. The collected data included the type of transfer, age, sex, type of trauma (head and face, neck, chest, abdomen, hands, feet, back, and genital area), distance from the hospital, primary vital signs (systolic blood pressure, heart rate, respiration rate and level of consciousness according to the Glasgow Coma Scale [GCS] ), duration of the mission (duration of arrival at the scene: receiving the mission until arrival at the scene, duration of presence at the scene: reaching the scene of the accident until the transfer to the hospital, duration of arrival at the hospital: movement from the scene of the accident to the arrival of the patients to the hospital) and the day of the accident (official holiday or weekend [Thursday and Friday], working days).
To control the confounders, we used propensity score matching using R software version 3.6.2. After matching, data analysis was performed by the t test and Chi-square test. A significance level less than 0.05 was considered for the two-tailed tests. Outcomes studied included length of hospital stay, intensive care unit, duration of mechanical ventilation, and need for immediate surgery. The duration of hospitalization in the hospital and intensive care unit was measured in days, and the duration of mechanical ventilation was measured in hours. The need for immediate surgery was defined as surgery in the first 24 hours of hospitalization. The generalized linear model evaluated the outcome of the length of hospital stay, length of stay in the intensive care unit, and duration of mechanical ventilation. Logistic regression was used to analyze the outcome of the need for immediate surgery. This article is part of an approved Master’s degree dissertation submitted to Qom School of Nursing, approved by the Ethics Committee of Qom University of Medical Sciences (Code: IR.MUQ.REC.1399.067).

3. Results
Out of all injured people, 1075(4.7%) were transported to the hospital by helicopter and 22124(95.3%) by ambulance. The patients included 566 air emergency patients and 1491 ground road emergency patients. After matching the two groups, the number of patients in each ground and air group reached 566 (Figure 1).

Most of the patients were men (62.3%). The Mean±SD age of the patients was 30.64±16.39 years. The Mean±SD distance of the patients was 39.12±20.84 km. The Mean±SD time to reach the scene of the accident was 12.12±7.7 minutes and the Mean±SD time to be present at the scene of the accident was 15.39±10.56 minutes and the Mean±SD time to transfer the patients to the hospital was 15.46±5.10 minutes (Table 1).

The incidence of traffic accidents on holidays and weekends in air emergencies was higher (53%) (P=0.028). Head and face trauma was higher in air emergency patients (9.2%) (P=0.028). Also, back trauma was more in this group (21.7%) (P=0.002). Duration of arrival at the scene in air emergency patients were significantly longer than ground emergency patients (7.70±5.18 min) (P<0.001). But duration of presence at the scene (12.17±8.33)(P=0.041) and duration of arrival at the hospital (13.12±4.75) (P<0.001) in air emergency patients were significantly shorter than ground emergency patient.
Ground emergency patients stayed 0.15 days (about 3.6 hours) more than air emergency patients in the intensive care unit, but this difference was not statistically significant (P=0.718). The length of hospital stay increases by 0.93 days (approximately 22.3 hours) per unit reduction in the GCS before treatment (P<0.001). Injured patients with leg trauma were hospitalized in the intensive care unit for 1.11 days (about 26.6 hours) more than non-traumatized patients (P=0.005).
Ground emergency patients were under mechanical ventilation 8.40 hours longer than that for air emergency patients, but this difference was not significant (P=0.507). Male patients were under mechanical ventilation 9.93 hr longer than female patients (P<0.001). This time increases for each unit decrease in GCS before arriving the hospital by 14.82 hr (P<0.001). Also, the patients with leg trauma were mechanically ventilated for about 22 hr more than those without leg trauma (P=0.004).
Air emergency patients were hospitalized in the hospital 1.27 days (about 30.6 hours) more than ground emergency patients, but this increase was not significant (P=0.089). This period increases by 1.58 days (approximately 37.9 hours) per unit decrease in GCS (P<0.001). Also, the patients people with abdominal trauma were hospitalized 2.63 days (about 63.2 hours) more than injured people without abdominal trauma (P<0.001) and the patients with leg trauma for 2.70 days (approximately 64.8 hours) more than the patients without leg trauma (P<0.001) (Table 2).

The chance of surgery in air emergency patients is 84.8% higher than ground emergency patients (95%CI: 0.086-0.267; P<0.001). The chance of immediate surgery in patients with head and face trauma is 41.6% higher than patients without head and face trauma (95%CI: 0.423-0.807; P=0.001). The chance of immediate surgery in patients with abdominal trauma is 55.8% higher than those without abdominal trauma (95%CI: 0.718-0.272; P=0.001). The chance of immediate surgery in patients with back trauma is 49% higher than patients without back trauma (95%CI: 0.338-0.743 P=0.001) (Table 3).

4. Discussion
The present study used prehospital and hospital information of traffic accident patients and analyzed them to evaluate the outcome of road traffic accident patients regarding the transfer method. Considering the relatively recent use of helicopters in transporting the patients in Qom Province, our findings can help evaluate and inform practical, evidence-based solutions for prehospital transportation of the patients. This study compared the outcome of patients in a type of trauma caused by a traffic accident just outside the city, transported by nurses and paramedics with the same continuing training courses, by helicopter, in a province, to a hospital. These criteria prevent or reduce the damaging effects. In addition, to minimize the bias of selecting air or ground emergency patients, a propensity score matching was used to adjust the variables. The use of generalized linear model analysis and logistic regression methods also increased the study’s accuracy.
In the present study, 4.7% of the patients were transported by air emergency. A study by Abe et al. in Japan shows that 8.6% of patients were transported by air. This study was performed on different types of trauma and was not specific to traffic accidents [16]. Three previous studies from Germany also reported more use of air emergencies (31.2%-37.7%) [19, 27, 28]. In some prehospital systems, the transfer of urban patients is also done by air, but in Qom Province, air emergency is not sent to inside city missions. This issue can make a difference in the use of air emergencies.
The time to reach the accident scene in the air emergency was longer than the ground emergency. Some factors can affect this time. According to a study by al-Thani et al. in Qatar, due to the weather conditions, the helicopter must be stationed inside the hangar, and it takes approximately 7 minutes for the air emergency to be ready to fly [11]. But the Qom emergency helicopter is not in the hangar, and this period is probably shorter. Nevertheless, much time is spent preparing and coordinating air emergency flights that could not be accounted for in the present study. This time of preparation and coordination increases the time to reach the accident scene. Ground-based road emergency bases are also located in the area and are sent on a traffic accident mission. Still, the air emergency is located in Qom and needs to be sent for a longer distance (53.11 ±18.30 km) than the ground emergency (25.13 ±11.93 km). The average duration of presence at the scene in the air emergency was less than the ground emergency. This result is in line with the study of Eghbali et al. in Qom [29]. 
In Qom Province, a direct air ambulance is not usually sent to the scene. First, a ground emergency is sent to the scene, and then an air emergency. In a situation where the number of injured is high, and there is a need to transfer some injured by the ground emergency, the ground emergency remains at the scene until the air emergency arrives and delivers the patients, and then the patients are transferred to the hospital. This procedure can affect the duration of presence at the scene in the ground emergency. The average transfer time from the accident scene to the hospital was also shorter in the air emergency. The arrival time at the hospital is usually announced when the helicopter grounds at the hospital. The helicopter grounding pad is located in the open area of Shahid Beheshti Hospital in Qom, and the patients are transported from the yard to the emergency department by a hospital ambulance. This time required to transfer from the pad to the emergency department is not calculated and recorded, but the patients of the ground emergency go directly to the hospital’s emergency department. 
In severely injured and time-sensitive injuries, cutting the duration of presence at the scene and transporting the patients to a hospital may be a valuable component of an air emergency. Therefore, given the greater chance of emergency surgery in air emergency patients, a different outcome might have occurred if these patients had been transported by ground emergency. Although in this study, air emergency showed a shorter duration of presence at the scene and transfer to the hospital, in some studies, no correlation was observed between the time and outcome of the patients. After adjusting for the severity of the injury and the characteristics of the patients, Ringburg et al. found no association between the long duration of the arriving scene and the death [30]. Newgard et al. also evaluated the golden hour in the prehospital emergency department. They found that shorter prehospital time was ineffective in survival in traumatic adults [23]. Brown et al. examined prehospital time in ground and air emergency patients. They found that only prehospital airway transfer time between 6 and 30 minutes increases survival, while transfer time less than 5 minutes and more than 30 minutes was not affected by the type of transport [7].
In this study, the difference in the length of hospital stay in the two groups of air and ground emergencies was not significant. The length of hospital stay varies in different studies [11, 15, 31]. In the study of Michael et al., the average length of hospital stay in the air emergency (8 days) was significantly longer than the ground emergency (5.2 days). But Kim et al. stated that this value does not differ between the two groups [4]. In the present study, the difference in the length of hospital stay was not only related to the type of transfer to the hospital but also several other factors, including male gender, older age, decreased level of consciousness before the hospital, and type of trauma to the abdomen and legs. It may also be related to the severity of the injury, underlying illness and medical history, and the actions of the hospital team that were not examined in this study. In the present study, the difference in the length of hospital stay in the intensive care unit between the air and ground emergency groups was not significant. 
The difference in the length of hospital stay in the intensive care unit is significant in some studies [4, 11, 15]. In the study of Michael et al., the mean duration of hospitalization in the intensive care unit in the air emergency (3 days) was longer than the ground emergency (0.5 days). In the present study, this period was longer for the patients of the ground emergency. In this study, male gender, older age, decreased level of consciousness before the hospital, and the type of leg trauma during hospitalization in the intensive care unit were influential factors. In this study, the type of injury was examined, but the severity of the injury to different parts of the body was not determined, a factor that could be effective during your stay in the intensive care unit. Also, in this study, there was no significant difference between air and ground emergency patients in the duration of mechanical ventilation. The duration of mechanical ventilation of air and ground emergency patients was significantly different in the study of Michael et al. [15] but was not significant in some studies [7, 11, 31]. In the present study, male gender, older age, decreased level of consciousness before the hospital, and leg trauma increased the chance of mechanical ventilation in traffic accident patients. The need for immediate surgery was greater in air emergency patients than in ground emergency patients. Some studies have not found a significant difference in the need for immediate surgery [4, 7, 31]. In this study, air emergency transfer, older age, increasing the duration of the presence and duration of the transfer, the trauma to the head and face, abdomen, legs, back, and transfer during the holidays and weekends, show an increase in the need for immediate surgery. With older age, the length of hospital stay and intensive care unit and mechanical ventilation, and the need for immediate surgery increases. Hranjek et al. found that the severity of the injury, blood pressure, and mechanical ventilation were independent predictors of mortality in the elderly [32]. Therefore, more attention should be paid to the triage of the elderly injured.
One of the factors affecting the outcome of the patients is the triage at the scene of the accident, and based on that, the choice of transfer method is chosen. Because of the small area of Qom Province (11526 km2), which is the second smallest province in Iran [25], the long distance from the hospital was probably not the main reason for using the air emergency, but age and clinical condition, such as the severity of injury and level of consciousness, significantly affect the use of air emergency. Gries et al. evaluated 2111 patients and reported no clinical advantage in sending an air ambulance regardless of triage criteria. The researchers suggested that the presence of an emergency physician on the scene and the care of complex emergencies and the reduction of prehospital time should be the primary uses of air emergencies [18]. According to the findings of Shaw et al. and Verkreus et al., a prehospital system should use more straightforward and more accurate criteria to reduce overuse of air emergencies and demonstrate the benefits of time and survival [33, 34]. For more effective use of air emergencies, basic guidelines should focus on clear criteria for reducing prehospital transfer time, clinical triage (level of consciousness and severity of injury), and environmental factors (access to ground emergency and distance from hospital). 
Researchers often debate whether air emergency was cost-effective in survival gains in the case of higher-level triage of minor injuries, higher costs, or the risk of transportation in air emergency versus ground emergency [17, 35, 36, 37]. Delgado et al. addressed these issues in their cost-effectiveness model based on the relative reduction in mortality risk, higher triage, transfer cost and risk, and other factors. They found that air emergencies would be cost-effective by reducing the transfer of minor injuries or improving the outcome of long-term disability and caused at least a 15% reduction in deaths or a significant improvement in long-term disability [13].
This observational study may have intrinsic defects, including the possibility of incorrect information entry. The present data may have a measurement error. This study lacks the Severity Injury Scale (ISS) data. This study limited its analysis to the initial outcome at the hospital and did not evaluate the long-term outcome in the patients. We did not analyze the effect of the type of treatment on the scene on the outcome of the patients. The present study may not be generalizable to other geographical areas. For these reasons, larger studies in different areas need to be repeated to prove the findings.

5. Conclusion
There was no significant difference between air and ground emergency patients in the duration of hospitalization in the intensive care unit, duration of mechanical ventilation, and length of hospital stay. Air emergency patients needed more immediate surgery. In general, male patients, old age, decreased level of consciousness before the hospital, and leg traumas were predictors of increased length of hospital stay, intensive care unit, and mechanical ventilation. Older age, longer stay at the accident scene and transfer to the hospital, trauma to the head and face, abdomen, back, legs, and transfer during the holidays and weekends were predictors of an increased need for immediate surgery. This study can determine the criteria of clinical triage and key environmental factors. If the patients are properly triaged based on the type of injury and the level of consciousness before arriving at the hospital and transferred to the hospital by air emergency for treatment, they can enjoy the benefits of the transfer type. More research is needed to make the best use of air emergencies and identify relevant subgroups.

Ethical Considerations
Compliance with ethical guidelines
This article was approved by the Ethics Committee of Qom University of Medical Sciences (Code: IR.MUQ.REC.1399.067). 

Funding
This study was financially supported by Qom University of Medical Sciences.

Authors' contributions
All authors equally contributed to preparing this article.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The researchers would like to thank all the colleagues of the School of Nursing and 115 Qom Emergency Personnel who collaborated in this research.


References

1. World Health Organization (WHO). Global status report on road safety 2018 [Internet]. 2018 [Updated 2018 July 17]. Available from: https://www.who.int/publications/i/item/9789241565684
2. Pandya SR, Yelon JA, Sullivan TS, Risucci DA. Geriatric motor vehicle collision survival: The role of institutional trauma volume. Journal of Trauma. 2011; 70(6):1326-30. [DOI:10.1097/TA.0b013e31820e327c] [PMID]
3. McGarvey C, Hamilton K, Donnelly J, Nicholson AJ. Trends in road transport collision deaths in the Irish paediatric population: A retrospective review of mortality data, 1991-2015. BMJ Paediatrics Open. 2019; 3(1):e000361. [DOI:10.1136/bmjpo-2018-000361] [PMID] [PMCID]
4. Kim OH, Roh YI, Kim HI, Cha YS, Cha KC, Kim H, et al. Reduced mortality in severely injured patients using hospital-based helicopter emergency medical services in interhospital transport. Journal of Korean Medical Science. 2017; 32(7):1187-94. [DOI:10.3346/jkms.2017.32.7.1187] [PMID] [PMCID]
5. Forensic Medicine Organization. Statistics of deaths and injuries from traffic accidents referring to forensic medicine centers of Iran [Internet]. 2019. Available from: ^{https://www.lmo.ir/web_directory/53999.html: 2018 30/9/2019}
6. Pham H, Puckett Y, Dissanaike S. Faster on-scene times associated with decreased mortality in Helicopter Emergency Medical Services (HEMS) transported trauma patients. Trauma Surgery & Acute Care Open. 2017; 2(1):e000122. [DOI:10.1136/tsaco-2017-000122] [PMID] [PMCID]
7. Brown JB, Gestring ML, Guyette FX, Rosengart MR, Stassen NA, Forsythe RM, et al. Helicopter transport improves survival following injury in the absence of a time-saving advantage. Surgery. 2016; 159(3):947-59. [DOI:10.1016/j.surg.2015.09.015] [PMID] [PMCID]
8. World Health Organization (WHO). Post-crash response: Supporting those affected by road traffic crashes [Internet]. 2016 [Updated 2016 October 30]. Available from: https://www.who.int/publications/i/item/post-crash-response-supporting-those-affected-by-road-traffic-crashes
9. Abrahamsen EB, Selvik JT, Dahle AN, Asche F, Abrahamsen HB. A socio-economic analysis of increased staffing in the Norwegian helicopter emergency medical service. Scandinavian Journal of Trauma, Resuscitation and Medicine. 2018; 26(1):83. [DOI:10.1186/s13049-018-0548-4] [PMID] [PMCID]
10. Widener MJ, Ginsberg Z, Schleith D, Floccare DJ, Hirshon JM, Galvagno S. Ground and helicopter emergency medical services time tradeoffs assessed with geographic information. Aerospace Medicine and Human Performance. 2015; 86(7):620-7. [DOI:10.3357/AMHP.4173.2015] [PMID]
11. Al-Thani H, El-Menyar A, Pillay Y, Mollazehi M, Mekkodathil A, Consunji R. In-hospital outcome based on the mode of ems transportation in a high-income rapidly developing middle eastern country. Global Journal of Health Science. 2017; 9(2):246-55. [DOI:10.5539/gjhs.v9n2p246]
12. Galvagno Jr SM, Sikorski R, Hirshon JM, Floccare D, Stephens C, Beecher D, et al. Helicopter emergency medical services for adults with major trauma. Cochrane Database of Systematic Reviews. 2015; 2015(12):CD009228. [DOI:10.1002/14651858.CD009228.pub3] [PMID] [PMCID]
13. Delgado MK, Staudenmayer KL, Wang NE, Spain DA, Weir S, Owens DK, et al. Cost-effectiveness of helicopter versus ground emergency medical services for trauma scene transport in the United States. Annals of Emergency Medicine. 2013; 62(4):351-64.e19. [DOI:10.1016/j.annemergmed.2013.02.025] [PMID] [PMCID]
14. Stewart KE, Cowan LD, Thompson DM, Sacra JC, Albrecht R. Association of direct helicopter versus ground transport and in‐hospital mortality in trauma patients: A propensity score analysis. Academic Emergency Medicine. 2011; 18(11):1208-16. [DOI:10.1111/j.1553-2712.2011.01207.x] [PMID]
15. Michaels D, Pham H, Puckett Y, Dissanaike S. Helicopter versus ground ambulance: Review of national database for outcomes in survival in transferred trauma patients in the USA. Trauma Surgery & Acute Care Open. 2019; 4(1):e000211. [DOI:10.1136/tsaco-2018-000211] [PMID] [PMCID]
16. Abe T, Takahashi O, Saitoh D, Tokuda Y. Association between helicopter with physician versus ground emergency medical services and survival of adults with major trauma in Japan. Critical Care. 2014; 18(4):R146. [DOI:10.1186/cc13981] [PMID] [PMCID]
17. Galvagno SM, Haut ER, Zafar SN, Millin MG, Efron DT, Koenig GJ, et al. Association between helicopter vs ground emergency medical services and survival for adults with major trauma. JAMA. 2012; 307(15):1602-10. [DOI:10.1001/jama.2012.467] [PMID] [PMCID]
18. Gries A, Lenz W, Stahl P, Spiess R, Studiengruppe B. [On-scene times for helicopter services. Influence of central dispatch center strategy (German)]. Anaesthesist. 2014; 63(7):555-62. [DOI:10.1007/s00101-014-2340-9] [PMID]
19. Andruszkow H, Schweigkofler U, Lefering R, Frey M, Horst K, Pfeifer R, et al. Impact of helicopter emergency medical service in traumatized patients: Which patient benefits most? PLoS One. 2016; 11(1):e0146897. [DOI:10.1371/journal.pone.0146897] [PMID] [PMCID]
20. Bekelis K, Missios S, Mackenzie TA. Prehospital helicopter transport and survival of patients with traumatic brain injury. Annals of Surgery. 2015; 261(3):579-85. [DOI:10.1097/SLA.0000000000000672] [PMID] [PMCID]
21. Al-Thani H, El-Menyar A, Latifi R. Prehospital versus emergency room intubation of trauma patients in Qatar: A -2- year observational study. North American Journal of Medicine and Science. 2014; 6(1):12-8. [DOI:10.4103/1947-2714.125855] [PMID] [PMCID]
22. Stewart CL, Metzger RR, Pyle L, Darmofal J, Scaife E, Moulton SL. Helicopter versus ground emergency medical services for the transportation of traumatically injured children. Journal of Pediatric Surgery. 2015; 50(2):347-52. [DOI:10.1016/j.jpedsurg.2014.09.040] [PMID]
23. Newgard CD, Schmicker RH, Hedges JR, Trickett JP, Davis DP, Bulger EM, et al. Emergency medical services intervals and survival in trauma: Assessment of the “golden hour” in a North American prospective cohort. Annals of Emergency Medicine. 2010; 55(3):235-46.e4. [DOI:10.1016/j.annemergmed.2009.07.024] [PMID] [PMCID]
24. Young Journalist Club. Inauguration of Qom air emergency base with the presence of the minister of health (Persian) [Internet]. 2014 [Updated 2014 August 9]. Available from: https://www.yjc.news/00Kis0
25. Razzaghi A, Soori H, Kavousi A, Abadi A, Khosravi A. Factors with the highest impact on road traffic deaths in Iran: An ecological study. Archives of Academic Emergency Medicine. 2019; 7(1):e38. [PMID]
26. Parvaresh MM, Asayesh H, Haji MHM, Jodaki K, Bagheri MJ, Jamshidi M. [Epidemiology of road accident death in Qom Province, 2014 (Iran) (Persian)]. Qom University of Medical Sciences Journal. 2017; 11(8):94-100. http://journal.muq.ac.ir/article-1-962-en.html
27. Andruszkow H, Lefering R, Frink M, Mommsen P, Zeckey C, Rahe K, et al. Survival benefit of helicopter emergency medical services compared to ground emergency medical services in traumatized patients. Critical Care. 2013; 17(3):R124. [DOI:10.1186/cc12796] [PMID] [PMCID]
28. Andruszkow H, Hildebrand F, Lefering R, Pape HC, Hoffmann R, Schweigkofler U. Ten years of helicopter emergency medical services in Germany: Do we still need the helicopter rescue in multiple traumatised patients? Injury. 2014; 45(Suppl 3):S53-8. [DOI:10.1016/j.injury.2014.08.018] [PMID]
29. Hamta A, Kazemnejad A, Gholami Fesharaki M, Farhadi R. Effectiveness of cervical cerclage on preterm delivery and neonatal outcome in twin pregnancies: Propensity score matching analysis. Iranian Red Crescent Medical Journal. 2017; 19(5):e40600. [DOI:10.5812/ircmj.40600]
30. Ringburg AN, Spanjersberg WR, Frankema SP, Steyerberg EW, Patka P, Schipper IB. Helicopter Emergency Medical Services (HEMS): Impact on on-scene times. Journal of Trauma and Acute Care Surgery. 2007; 63(2):258-62. [DOI:10.1097/01.ta.0000240449.23201.57] [PMID]
31. Zhu TH, Hollister L, Opoku D, Galvagno Jr SM. Improved survival for rural trauma patients transported by helicopter to a verified trauma center: A propensity score analysis. Academic Emergency Medicine. 2018; 25(1):44-53. [DOI:10.1111/acem.13307] [PMID] [PMCID]
32. Hranjec T, Sawyer RG, Young JS, Swenson BR, Calground JF. Mortality factors in geriatric blunt trauma patients: Creation of a highly predictive statistical model for mortality using 50,765 consecutive elderly trauma admissions from the National Sample Project. The American Surgeon. 2012; 78(12):1369-75. [DOI:10.1177/000313481207801229] [PMID] [PMCID]
33. Shaw JJ, Psoinos CM, Santry HP. It’s all about location, location, location: A new perspective on trauma transport. Annals of Surgery. 2016; 263(2):413-8. [DOI:10.1097/SLA.0000000000001265] [PMID] [PMCID]
34. Vercruysse GA, Friese RS, Khalil M, Ibrahim-Zada I, Zangbar B, Hashmi A, et al. Overuse of helicopter transport in the minimally injured: A health care system problem that should be corrected. Journal of Trauma and Acute Care Surgery. 2015; 78(3):510-5. [DOI:10.1097/TA.0000000000000553] [PMID]
35. Sullivent EE, Faul M, Wald MM. Reduced mortality in injured adults transported by helicopter emergency medical services. Prehospital Emergency Car. 2011; 15(3):295-302. [DOI:10.3109/10903127.2011.569849] [PMID]
36. Brown JB, Forsythe RM, Stassen NA, Gestring ML. The National Trauma Triage Protocol: Can this tool predict which patients with trauma will benefit from helicopter transport? Journal of Trauma and Acute Care Surgery. 2012; 73(2):319-25. [DOI:10.1097/TA.0b013e3182572bee] [PMID]
37. Brown JB, Leeper CM, Sperry JL, Peitzman AB, Billiar TR, Gaines BA, et al. Helicopters and Injured Kids: Improved survival with scene air medical transport in the pediatric trauma population. Journal of Trauma and Acute Care Surgery. 2016; 80(5):702-10. [DOI:10.1097/TA.0000000000000971] [PMID] [PMCID]