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HEMS vs. EMS Transfer for Acute Aortic Dissection Type A
ORIGINAL RESEARCH
HEMS vs. EMS Transfer for Acute Aortic Dissection Type A Karsten Knobloch, MD, PhD,1 Imke Dehn, MD,1 Nawid Khaladj, MD,2 Christian Hagl, MD, PhD,2 Peter M. Vogt, MD, PhD,1 and Axel Haverich, MD, PhD2
Abstract Background: We thought to evaluate the impact of the mode of physician-based transportation (helicopter emergency medical service [HEMS] vs. ground-based emergency medical service [EMS]) on short- and long-term survival among patients suffering acute aortic dissection type A (AADA) as a primary end-point. Methods: One-hundred-seventy-seven AADA patients (59 ± 13 years) were included who were admitted to a cardiothoracic surgery department with comprehensive transfer documentation. Cox proportional hazard models and log-rank tests were performed as well as Kaplan-Meier survival curves. Follow-up was 93% over 5 ± 23⁄4 years. Results: Cox proportional hazard model found no mortality difference for HEMS versus EMS on primary transport (P = .5), as well as log-rank (Mantel Cox) on interhospital transport (P = 0.5). HEMS interhospital transfer was eightfold more expensive than EMS (HEMS, 3,871; EMS, 497; P = .01). Ninety-nine patients (56%) were alive at follow-up (mean survival, 1,153 days ± 1,124). Mortality after surgery was 2% (3/177) within the first hour, 5% (8/177) within 6 hours, 6% (10/177) within 12 hours, 11% (20/177) within 24 hours, 13% (23/177) within 48 hours, 14% (25/177) within 72 hours, and 26% (46/177) within 30 days after surgery. Conclusions: We found no advantage of survival rates among patients suffering from AADA who were transferred by either HEMS or EMS in primary or secondary transport. Although HEMS traveled a distance more than twofold longer than ground-based EMS at the same mission time, HEMS was eightfold more expensive than ground-based EMS in AADA.
Introduction The total incidence of thoracic aortic disease is unknown; however, the detection rate is increasing.1 An 1. Plastic, hand and reconstructive surgery, Hannover Medical School, Germany 2. Cardiothoracic and vascular surgery, Hannover Medical School, Germany Address for correspondence: Dr. Karsten Knobloch, MD, PhD, Plastic, Hand and Reconstructive Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany; [email protected] 1067-991X/$36.00 Copyright 2009 by Air Medical Journal Associates doi:10.1067/j.amj.200x.xx.xxx 146
aortic dissection type A has a false lumen of the ascending aorta with or without aortic arch participation (composing DeBakey type I + II). Acute aortic dissection type A (AADA) is defined as acute because the pathologic condition took place within 0 to 14 days of surgery. The mortality rate of patients with aortic dissection has been reported as 1% to 2% per hour for the first 24 to 48 hours.2 Also, Meszaros3 described a dramatic course of aortic dissections in a survey of 74 patients: 28.4% died within the first hour, 44.6% within 12 hours, 62.2% within 1 day, and 75.5% within 2 days. This high mortality rate has decreased because of the improvement of surgical therapy by introducing hypothermic circulatory arrest and antegrade cerebral perfusion.4 The occurrence of stroke is principally determined by patient-related and disease-related factors; however, use of cerebral perfusion can significantly reduce the occurrence of temporary neurologic dysfunction.5 An analysis of the international registry of acute aortic dissection showed that contemporary 1- and 3-year survival in patients with AADA treated surgically are excellent.6 Independent predictors of survival during the followup period do not appear to be influenced by in-hospital risks but rather by pre-existing co-morbidities. Therefore, the preclinical time from the very beginning of the symptoms until the start of the cardiothoracic surgical procedure might have an impact on the outcome of patients suffering AADA. This has not been addressed in previous studies. The aim of this investigation was to study whether secondary transfer to a level I cardiothoracic surgical center by helicopter emergency medical services (HEMS) is superior to ground emergency medical services (EMS) regarding long-term survival in Germany. In addition, we investigated the cost-effectiveness of HEMS and EMS. One has to acknowledge that we studied this preclinical situation in Germany, where both HEMS and EMS are equipped with a specially trained emergency physician at the scene, at least one paramedic, and a pilot in case of HEMS. The emergency physician at the scene is board-certified with special expertise in preclinical medicine, trauma, as well as intensive care medicine and intensive care interhospital transfer. Depending on the availability and immediacy of a given transport mode (HEMS or EMS), the emergency call dispatcher allocates an HEMS or EMS to the scene. In case of an interhospital transfer, the transferring hospital calls the emergency dispatcher, who seeks the fastest available Air Medical Journal 28:3
transportation vehicle to the transferring hospital. Typically, distances between 50 and 150 km are to be traveled in our geographic situation, which may not necessarily be the case in other geographic situations.
Methods Inclusion Criteria This study included all patients suffering an AADA surgery referred to Medical School Hannover with a complete HEMS or EMS transfer protocol (for either primary or secondary transfer) that are recorded and stored in the electronic data management system. This archive contains all clinical data of patients admitted since 1996.
Exclusion Criteria Exclusion criteria were all patients suffering aortic dissection Stanford type B despite complete HEMS or EMS transfer protocols, no existing HEMS/EMS protocol in aortic dissections type A, or no information of primary and secondary transportation. A total number of 365 patients suffering from AADA who were treated in the cardiothoracic and vascular department at Hannover Medical School in Germany were tested for eligibility. One hundred seventy-seven patients were eligible for inclusion in this study based on a complete HEMS or EMS transfer protocol. All of these 177 patients underwent emergency aortic surgery because of AADA between 1996 and 2005. The earliest surgery was performed in October 1987 and the latest in February 2005.
Data Collection • General parameters: Age at surgery, sex, date of death, date of hospital admission, distance of primary transfer, distance of secondary transfer, predispositions • Premedical parameters: Date and time of pain, localization and character of pain, unconsciousness, general complaints, place of rescue, recipient of emergency call • Transfer parameters for primary and secondary transport (see Definitions): Date and time of alarm, departure to patient, arrival at patient, handing over, departure to hospital, arrival at hospital, time of transfer, way of transportation (helicopter [HEMS] or ground based [EMS]), accompanying professionals, self-transportation, destination self- transportation, consciousness, Glasgow Coma Scale, systolic and diastolic blood pressure, pulse • Primary hospital: Arrival date, arrival time, symptoms, systolic blood pressure, diastolic blood pressure, pulse, diagnostics • Medical School Hannover: Arrival date, arrival time, diagnostics, motor disorder, blood pressure, pulse, anaesthesia, intubations, surgery date, surgery time, cross-clamp time, time on heart lung machine, time of cerebral perfusion, intensive care time, resuscitation, catecholamine May-June 2009
Follow-up Follow up was performed by direct telephone interview with the patients or relatives. Telephone calls were made to patients’ general practitioners, or a written questionnaire was mailed. The follow-up was 93% (166 cases) complete. End of research was August 1, 2006 (last interview). Mean time of follow-up was 1,881 ± 1,026 days (5 ± 23⁄4 years). Telephone interviews were done based on a standardized questionnaire. In case of death of the patient, a thorough analysis was done regarding date and detailed cause of death with the relatives.
Definitions • Acute aortic dissection type A: AADA was defined as acute because the pathologic condition took place within 0 to 14 days of surgery. An aortic dissection type A has a false lumen of the ascending aorta with or without aortic arch participation (DeBakey types I and II). • Mortality: Early mortality was defined as 30-day mortality. Overall mortality was mortality from date of aortic surgery to the end of the follow-up period. It includes mortality associated with cardiac diseases and mortality not associated with cardiac diseases. • Survival: Survival was defined as survival longer than a certain time t. Survival function represents the likelihood of living at time t of a given individual. • Mode of transport: Primary transport is transfer from the place of accident (scene) to the primary hospital (first hospital reached and approached during rescue). Primary transport is equivalent to rescue. Secondary transport is transfer from the primary hospital to the cardiothoracic surgical department (interhospital transfer). Paramedic transport is carried out by paramedics without an emergency doctor. Self-transport is not accompanied by any medical staff. • Costs: Costs of ground transport were separated into costs for doctor on call and emergency ambulance. An emergency doctor costs 315 for the first hour and 100 every additional hour. Emergency ambulance costs 228, including the first 20 km. Every additional kilometer costs 2.48. Helicopter transport costs 53 per helicopter minute in air, assumed that a helicopter travels at 3 km/min. Information on cost is based on personal communication with the responsible emergency dispatching center and the rescue organizations in the region of Hannover, Germany.
Patient Characteristics Age at AADA surgery was at mean 59 ± 13 years. The youngest patient recorded was 20 years old, and the oldest patient was 86 years old. One hundred fourteen patients (64%) were male, and 63 patients (36%) were female. Three percent (5/177) were transported primarily by HEMS and 24% (42/177) by EMS. In secondary transport, 25% (39/156 patients) had HEMS, and 58% (91/156 patients) had EMS transport. Patients` characteristics were divided into two groups of HEMS (group A) and EMS (group B) (Table 1). 147
Table 1. Patients’ characteristics as well as cardiothoracic surgical parameters for helicopter emergency medical service [HEMS; n=39] (Group A) and ground-based emergency medical service [EMS; n=91] (Group B). 2-tailed independent samples t-test showed no differences between HEMS and EMS HEMS (Group A) EMS (Group B) p value value Patients assessed value Patients assessed (A vs B) Age at surgery (years) 57±15 39/39 58±12 91/91 0.81 Number of peripheral vein catheters 2±1 23/39 2±1 33/91 0.71 Arterial catheter 1±0 5/39 1±0 2/91 Not performed Central venous catheter 1±0 11/39 1±0 13/91 Not performed Time of surgery (min) 256±65 39/39 278±110 91/91 0.24 Time cerebral perfusion (min) 23±15 39/39 26±11 91/91 0.35 Cross-clamp-time (min) 117±45 39/39 113±40 91/91 0.76 Time of intubation (min) 52±60 39/39 78±129 91/91 0.23 Resuscitation postsurgical No 33/39 No 84/91 0.69 Yes 6/39 Yes 7/91 Catecholamines postsurgical No 20/39 No 45/91 0.79 Yes 18/39 Yes 45/91 Days at intensive care unit 5±8 39/39 5±6 91/91 0.79
In 47 (27%) of 177 patients, primary transfers protocols could be analyzed. Twenty-one patients (12%) of 177 were directly transferred to Hannover Medical School (level I cardiothoracic and vascular surgery center) and 26 patients (15%) to regional hospitals. One-hundred-fiftysix patients (88%) had been transferred from a regional hospital to Hannover Medical School (level I cardiothoracic and vascular surgery center).
Statistical Analysis A P value less than .05 was considered statistically significant for all analyses. Survival functions were calculated and displayed by Kaplan-Meier curves. Modes of primary transport were analyzed by Pearson chi-square test. Modes of secondary transportation were analyzed by Kaplan-Meier survival curves compared using log-rank tests. Comparison of HEMS and EMS was done by twoFigure 1. Thirty-day mortality after AADA surgery, displayed by Kaplan-Meier curves.
tailed independent samples t-test. Distance of transportation and transfer times have been analyzed with regard to the survival by a Cox proportional hazard model, as well as the two-tailed independent samples t-test, also described by box-plots. Comparison of costs of primary and secondary transportation was done using the twotailed independent samples t-test and was described by box-plots. Statistical analysis was performed using SPSS 13 software (SPSS Inc., Chicago, IL).
Results Survival Rates Ninety-nine patients (56%) were alive at follow-up 3.5 years after AADA. Forty-six patients (26%) died during the first 30 days after surgery, and 21 patients (12%) died after the first 30 days postsurgery (Figs. 1, 2). Sixty-two patients (35%) died during the first year after surgery.
Mortality after Cardiothoracic Surgery Mortality after surgery was 2% (3/177) within the first hour, 5% (8/177) within 6 hours, 6% (10/177) within 12 hours, 11% (20/177) within 24 hours, 13% (23/177) within 48 hours, 14% (25/177) within 72 hours, and 26% (46/177) within 30 days after surgery. Twenty patients (11%) died of non–cardiac-associated reasons. Mean survival was 1,153 ± 1,124 (31⁄2 years ± 31⁄4).
Primary Transfer Type of Transfer: The choice of primary transport vehicle was not significant for survival (P = .78; Pearson chisquared). Independent samples t-test showed no significant difference in transportation distance of HEMS and EMS (P = .76). Cox proportional hazard model showed no significance for primary distances (30-day mortality, P = .545; overall mortality, P = .516). 148
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Figure 2. Overall mortality after AADA surgery, displayed by Kaplan-Meier curves.
way and return. Costs of HEMS were 836 ± 530 (5/157), based on 36 ± 26 km (5/157). Independent samples t-test showed no significant difference in costs of primary transportation between HEMS and EMS (P = 2.02).
Secondary Transfer
Figure 3. No significant difference in 30-day mortality (P = .5, logrank test) was seen between HEMS (n = 39) and EMS (n = 91), displayed by Kaplan-Meier curves.
Figure 4. No significant difference in overall mortality (P = .5, logrank test) was seen between HEMS (n = 39) and EMS (n = 91), displayed by Kaplan-Meier curves.
Type of Secondary Transfer: No significance was evident for secondary transfer by HEMS versus EMS regarding longterm mortality (P = 0.5) (Figs. 3, 4). Independent samples t-test showed no significant differences between HEMS and EMS, except the distance traveled during secondary transport (Tables 2–4). HEMS covered a distance of 110 ± 79 km and EMS a distance of 41 ± 57 (P = .01). Independent samples t-test showed a significant difference in transportation distance of HEMS in contrast to EMS in secondary transportation (P = 0.01) (Fig. 5). Cox proportional hazard model showed no significance of difference in transportation distance on mortality (30-day mortality, P = .623; overall mortality, P = .278). Independent samples t-test did not show any significant difference in transportation time of HEMS and EMS in secondary transportation (P = .76) (Fig. 6). Cox proportional hazard model showed no significance of difference in transportation time on mortality (30-day mortality, P = .9; overall mortality, P = .87). Time for alarm was analyzed in detail for secondary transport: • Time from alarm to arrival of secondary transport vehicle at primary hospital: HEMS (6/39) 66 ± 46 min; EMS (4/91) 48 ± 116 minutes • Time from alarm to patient´s arrival at Medical School Hannover: HEMS (6/39) 124 ± 63 minutes; EMS (6/91) 116 ± 98 minutes Costs of Secondary Transport: Secondary transfer costs in EMS were 497 ± 720 (82/156), calculated on 68 ± 78 minutes) emergency doctor time (81/156) and 137 ± 102 km emergency ambulance transport (82/156) one way and return. Secondary HEMS was 3,871 ± 2,790, based on 219 ± 158 km (39/156) one way and return. Independent samples t-test showed a significant difference in costs of secondary transportation (P = .01) (Fig. 7). HEMS secondary transfer for AADA was eight times more expensive than EMS.
Discussion
Costs of Primary Transport: Ground-based primary transport costs 296 ± 543 (33/157) based on 75 ± 96 minutes for doctor on call (26/157) and 25 ± 28 km for the emergency ambulance (33/157). Calculation was done with correction for self-transportation. Calculation of costs was done oneMay-June 2009
We hypothetized that survival among patients suffering from AADA is influenced by the mode of interhospital transportation (HEMS vs. EMS). Interestingly, we could not detect a significant difference between HEMS in contrast to EMS for interhospital transfer regarding either short-term or long-term mortality up to 3.5 years after cardiothoracic surgery. This result has to be discussed in relation to the current emergency service situation in Germany. A board-certified emergency physician with special expertise in preclinicial medicine, trauma management, and interhospital transfer medicine is provided on both ground-based EMS and 149
Table 2. Time course from AADA symptoms to AADA surgery in a level-I cardiothoracic department for patients transferred by either helicopter emergency medical service [HEMS; n=39] (Group A) or emergency medical service [EMS; n=91] (Group B). 2tailed independent samples t-test showed significant differences between HEMS and EMS for secondary transfer distance (p=0.01). HEMS (Group A) EMS (Group B) p value value (n=39) value (n=91) (A vs B) Symptoms to primary hospital (min) 115±117 26/39 104±129 28/91 0.78 Time at primary hospital (min) 1587±2447 38/39 2088±2907 50/91 0.38 Time from alarm to arrival of secondary vehicle (min) 66±46 6/39 48±49 4/91 0.58 Time of secondary transfer (min) 39±19 39/39 37±42 91/91 0.77 Distance of secondary transfer (km) 110±79 39/39 41±57 91/91 0.01 Presurgery time at cardiothoracic surgery center (min) 520±1246 39/39 551± 1521 91/91 0.92
Table 3. AADA patients’ mental and physical status at primary transport by helicopter emergency medical service [HEMS; n=5] (Group A) or emergency medical service [EMS; n=42] (Group B). 2-tailed independent samples t-test showed no differences between HEMS and EMS. HEMS (Group A) EMS (Group B) p value value (n=5) value (n=42) (A vs B) Consciousness evident 5/5 evident 26/42 0.33 Lost 0/5 Lost 5/42 Glasgow Coma Scale 15±1 5/5 12±4 19/42 0.22 Systolic blood pressure (mmHg) 110±31 5/5 130±49 20/42 0.31 Diastolic blood pressure (mmHg) 60±18 4/5 73±16 11/42 0.26 Pulse 65±18 5/5 69±24 22/42 0.68 Motor disorders No 3/5 (15%) No 27/42 (64%) 0.13 Yes 2/5 (40%) Yes 4/42 (10%) Preclinical intubation/mechanical No 5/5 (100%) No 29/42 (70%) 0.56 ventilation Yes 0/5 Yes 2/42 (5%) Preclincial resuscitation No 5/5 (100%) No 30/42 (71%) 0.68 Yes 0/5 Yes 1/42 (1%) Catecholamines preclincal No 5/5 (100%) No 30/42 (71%) 0.68 Yes 0/5 Yes 1/42 (1%)
HEMS services. All 76 emergency helicopters throughout Germany are staffed with one emergency physician and at least one or two flight nurses. Furthermore, interhospital transfer of critical ill patients is feasible using a mobile intensive care unit, which is equipped with advanced respiratory and hemodynamic support facilities. We thought that the HEMS service might be superior to ground-based EMS, especially regarding the time of transfer. However, the transfer times were not significantly different despite the twofold longer distance traveled by HEMS versus EMS interhospital transfer. Thus, longer distances were traveled using HEMS versus EMS in the same time. The strength of this study is the currently largest patient cohort analyzed with a complete interhospital transfer protocol and the detailed perioperative and postoperative documentation. The follow-up was 93%, with 1,881 ± 1,026 days (5 ± 23⁄4 years). Based on the intrahospital, the 30-days, and 150
the long-term survival rates, we thought it would be appropriate to determine the effect size of the mode of transportation as the primary endpoint. Although survival among patients suffering AADA is multifactorial, time has been consistently identified as a crucial factor. Given the aforementioned report in acute aortic dissection type A, each hour until the cardiac operation will increase mortality by 1%. Currently there is no comparable published study determining the impact of the mode of preclinical or interhospital transportation among patients suffering from AADA. Stone et al7 found no difference of HEMS versus EMS interhospital transport among cardiac patients with unstable angina or myocardial infarction. Mitchell and Tallon8 analyzed a cohort of 34 patients suffering suspected aortic emergencies transferred by HEMS only. Boyd et al9 described a benefit of interhospital HEMS transport on trauma patients’ survival. Comparing HEMS Air Medical Journal 28:3
Table 4. AADA patients’ mental and physical status at secondary transport by helicopter medical service [HEMS; n=39] (Group A) or emergency medical service [EMS; n=91] (Group B). 2-tailed independent samples t-test showed no differences between HEMS and EMS. Parameters during secondary HEMS (Group A) EMS (Group B) p value transport (interhospital transfer) value (n=39) value (n=91) (A vs B) Consciousness evident 26/39 (67%) evident 38/91 (42%) 0.61 Lost 13/39 (33%) Lost 15/91 (16%) Glasgow Coma Scale 11±5 33/39 11±6 39/91 0.91 Systolic blood pressure (mmHg) 123±27 32/39 124±31 46/91 0.95 Diastolic blood pressure (mmHg) 70±20 28/39 70±16 35/91 0.93 Pulse 86±22 31/39 85±23 46/91 0.87 Motor disorders No 36/39 (92%) No 49/91 (54%) 0.97 Yes 3/39 (7%) Yes 4/91(4%) Interhospital intubation/mechanical No 29/39 (74%) No 39/91 (43%) 0.93 ventilation Yes 10/39 (26%) Yes 14/91 (15%) Interhospital resuscitation No 39/39 (100%) No 52/91 (57%) 0.39 Yes 0/39 Yes 1/91(1%) Interhospital catecholamines No 35/39 (90%) No 45/91 (49%) 0.49 Yes 4/39 (10%) Yes 8/91(9%)
versus EMS with regard to primary rescue, a broader number of studies have been published focusing on trauma patients. However, the role of HEMS in primary trauma transfer remains controversial regarding mortality. Whereas some, such as Cunningham et al,10 Fühler,11 and Biewener et al,12 found no confirmation of a better survival on HEMStransported patients, others, such as Frink et al13 and Mitchell et al,14 identified benefit on survival for HEMS rescue. Di Bartolomeo et al,15 who analyzed traumatic cardiac arrest, showed no significant benefit for HEMS in contrast to EMS. Conversely, HEMS transfer for patients suffering stroke seemed superior to ground-based EMS. Therefore, distinct clinical entities might exert a differential pattern regarding the outcome based on mode of transportation. It
has to be clearly pointed out that our preclinical and clinical situation with a dense network of HEMS and EMS with a huge overlap as well as no real remote areas might be somewhat different from some areas in northern America. Although HEMS traveled a distance more than twice as far as ground-based EMS for interhospital transfer (P = .01), this difference of distance was not significant regarding mortality because the time was the same. It is current practice that distance is a criterion for putting HEMS into action, at least in Germany. However, we found no significant difference between HEMS and EMS in secondary transfer time. Time from alarm for HEMS at primary hospital until arrival at primary hospital (66 minutes) and Medical School Hannover (124 minutes) was longer
Figure 5. HEMS (n = 39) traveled more than twofold longer secondary transport (interhospital) distances (P = .01; two-tailed independent samples t-test) than ground-based EMS (n = 115), displayed by box-plot.
Figure 6. No significant differences in secondary transport time (P = .76, two-tailed independent samples t-test) between HEMS (n = 39) and EMS (n = 74), displayed by box-plot.
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Figure 7. HEMS (n = 39) was eightfold more expensive (P = .01; two-tailed independent samples t-test) than EMS (n = 82), displayed by box-plot.
cohort of 177 patients suffering from AADA transferred to a single cardiothoracic center is the largest study to date, the patient cohort is still small in contrast, for example, to patients suffering from acute myocardial infarction. Acute aortic dissection type A is not a common diagnosis of chest pain. We performed a retrospective chart analysis with a prospective follow-up. A prospective randomized trial to compare EMS with HEMS might be a superior study design; however, this is limited in practice by a number of factors. We thought to standardize the study as much as possible by having a single cardiothoracic department perform all of the aortic surgery procedures. However, several distinct cardiac surgeons performed the procedures, which might confound the mortality rates as well.
Conclusions
than for EMS (48 minutes primary hospital/115 minutes Medical School Hannover). Nicholl17 analyzed activation time, response time, and on-scene time for HEMS, which was longer on average than for ground transport, but mostly depending on longer distances. Also, Ringburg18 described longer times for HEMS; however, when corrected for severity of trauma and patient characteristics, no influence on mortality of trauma patients could be seen. Frink et al13 showed no influence of longer HEMS rescue times on mortality of polytraumatized patients, in contrast to ground-based EMS. Besides mortality rates, we were interested in the calculated costs of either HEMS or EMS interhospital transfer. HEMS (3,871) was eightfold more expensive than EMS (497) for interhospital transfer of AADA patients. This is in line with Nicholl et al,17 calculating costs of HEMS as 595 pounds and EMS as 97 pounds. In 1997, Gearhart et al19 applied a cost-effectiveness analysis from the service provider’s perspective to cost and effectiveness estimates of HEMS for trauma patients. The effectiveness estimates were calculated with the trauma injury severity score (TRISS) methodology from literature sources and data from a cohort of patients transported by helicopter during 1994 and 1995. Transport costs were $2,214 per patient, and each additional survivor's hospitalization averaged $15,883. For the base case (five additional survivors per 100 patients flown), cost per life was $60,163, and discounted cost per year of life was $2,454. The authors assumed that helicopter air medical transport provides a substantial survival benefit for trauma patients, suggesting that this service is a cost-effective option for the treatment of trauma patients. However, these costs were calculated 12 years ago and do not necessarily correspond to various emergency medical systems over the world.
Limitations When interpreting our data, several limitations have to be taken into account. Despite the fact that the presented 152
We found no advantage of survival rates among patients suffering AADA transferred by either HEMS or EMS in primary or secondary transport. Although HEMS traveled a distance more than twofold longer than ground-based EMS at the same mission time, HEMS was eightfold more expensive than ground-based EMS in AADA.
References 1. Olsson C, Thelin S, Ståhle E, Ekbom A, Granath F. Thoracic aortic aneurysm and dissection: Increasing prevalence and improved outcomes reported in a nationwide population-based study of more than 14,000 cases from 1987 to 2002. Circulation 2006;114:2611-8. 2. Hirst AE Jr, Johns VJ Jr, Kime SW Jr. Dissecting aneurysm of the aorta: A review of 505 cases. Medicine (Baltimore) 1958;37:217-79. 3. Mészáros I, Mórocz J, Szlávi J, Schmidt J, Nagy L, Somogyi J, et al. Incidence and mortality of aortic dissection. Orv Hetil 1997;138:2783-8. 4. Nienaber C, Fattori R. Diagnosis and treatment of aortic diseases. Dordrecht: Kluwer Academic Publishers; 1999. 5. Hagl C, Ergin MA, Galla JD, Lansman SL, McCullough JN, Spielvogel D, et al. Neurologic outcome after ascending aorta-aortic arch operations: Effect of brain protection technique in high-risk patients. J Thorac Cardiovasc Surg 2001;121:1107-21. 6. Tsai TT, Evangelista A, Nienaber CA, Trimarchi S, Sechtem U, Fattori R, et al. Long-term survival in patients presenting with type A acute aortic dissection: Insights from the International Registry of Acute Aortic Dissection (IRAD). Circulation 2006;114(1 Suppl):I350-6. 7. Stone CK, Hunt RC, Sousa JA, Whitley TW, Thomas SH. Interhospital transfer of cardiac patients: Does air transport make a difference? Air Med J 1994;13:159-62. 8. Mitchell AD, Tallon JM. Air medical transport of suspected aortic emergencies. Air Med J 2002;21:34-7. 9. Boyd CR, Corse KM, Campbell RC. Emergency interhospital transport of the major trauma patient: air versus ground. J Trauma 1989;29:789-93; discuss. 793-4. 10. Cunningham P, Rutledge R, Baker CC, Clancy TV. A comparison of the association of helicopter and ground ambulance transport with the outcome of injury in trauma patients transported from the scene. J Trauma 1997;43:940-6. 11. Fühler, M. Die präklinische Versorgung des pädiatrischen Traumapatienten. Ein retrospektiver Vergleich zwischen luft- und bodenbebundener Rettung. Dissertation, Medizinische Hochschule Hannover; 2004. 12. Biewener A, Aschenbrenner U, Rammelt S, Grass R, Zwipp H. Impact of helicopter transport and hospital level on mortality of polytrauma patients. J Trauma 2004;56:94-8. 13. Frink M, Probst C, Hildebrand F, Richter M, Hausmanninger C, Wiese B, et al. The influence of transportation mode on mortality in polytraumatized patients: An analysis based on the German Trauma Registry. Unfallchirurgie 2007;110:334-40. 14. Mitchell AD, Tallon JM, Sealy B. Air versus ground transport of major trauma patients to a tertiary trauma centre: a province-wide comparison using TRISS analysis. Can J Surg 2007;50:129-33. 15. Di Bartolomeo S, Sanson G, Nardi G, Michelutto V, Scian F. HEMS vs. Ground-BLS care in traumatic cardiac arrest. Prehosp Emerg Care 2005;9:79-84.
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16. Conroy MB, Rodriguez SU, Kimmel SE, Kasner SE. Helicopter transfer offers a potential benefit to patients with acute stroke. Stroke 1999;30:2580-4. 17. Nicholl JP, Beeby NR, Brazier JE. A comparison of the costs and performance of an emergency helicopter and land ambulances in a rural area. Injury 1994;25:145-53. 18. Ringburg AN, Spanjersberg WR, Frankema SP, Steyerberg EW, Patka P, Schipper IB. Helicopter emergency medical services (HEMS): impact on on-scene times. J Trauma 2007;63:258-62. 19. Gearhart PA, Wuerz R, Localio AR. Cost-effectiveness analysis of helicopter EMS for trauma patients. Ann Emerg Med 1997;30:500-6.
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HEMS vs. EMS Transfer for Acute Aortic Dissection Type A Karsten Knobloch, MD, PhD,1 Imke Dehn, MD,1 Nawid Khaladj, MD,2 Christian Hagl, MD, PhD,2 Peter M. Vogt, MD, PhD,1 and Axel Haverich, MD, PhD2
Abstract Background: We thought to evaluate the impact of the mode of physician-based transportation (helicopter emergency medical service [HEMS] vs. ground-based emergency medical service [EMS]) on short- and long-term survival among patients suffering acute aortic dissection type A (AADA) as a primary end-point. Methods: One-hundred-seventy-seven AADA patients (59 ± 13 years) were included who were admitted to a cardiothoracic surgery department with comprehensive transfer documentation. Cox proportional hazard models and log-rank tests were performed as well as Kaplan-Meier survival curves. Follow-up was 93% over 5 ± 23⁄4 years. Results: Cox proportional hazard model found no mortality difference for HEMS versus EMS on primary transport (P = .5), as well as log-rank (Mantel Cox) on interhospital transport (P = 0.5). HEMS interhospital transfer was eightfold more expensive than EMS (HEMS, 3,871; EMS, 497; P = .01). Ninety-nine patients (56%) were alive at follow-up (mean survival, 1,153 days ± 1,124). Mortality after surgery was 2% (3/177) within the first hour, 5% (8/177) within 6 hours, 6% (10/177) within 12 hours, 11% (20/177) within 24 hours, 13% (23/177) within 48 hours, 14% (25/177) within 72 hours, and 26% (46/177) within 30 days after surgery. Conclusions: We found no advantage of survival rates among patients suffering from AADA who were transferred by either HEMS or EMS in primary or secondary transport. Although HEMS traveled a distance more than twofold longer than ground-based EMS at the same mission time, HEMS was eightfold more expensive than ground-based EMS in AADA.
Introduction The total incidence of thoracic aortic disease is unknown; however, the detection rate is increasing.1 An 1. Plastic, hand and reconstructive surgery, Hannover Medical School, Germany 2. Cardiothoracic and vascular surgery, Hannover Medical School, Germany Address for correspondence: Dr. Karsten Knobloch, MD, PhD, Plastic, Hand and Reconstructive Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany; [email protected] 1067-991X/$36.00 Copyright 2009 by Air Medical Journal Associates doi:10.1067/j.amj.200x.xx.xxx 146
aortic dissection type A has a false lumen of the ascending aorta with or without aortic arch participation (composing DeBakey type I + II). Acute aortic dissection type A (AADA) is defined as acute because the pathologic condition took place within 0 to 14 days of surgery. The mortality rate of patients with aortic dissection has been reported as 1% to 2% per hour for the first 24 to 48 hours.2 Also, Meszaros3 described a dramatic course of aortic dissections in a survey of 74 patients: 28.4% died within the first hour, 44.6% within 12 hours, 62.2% within 1 day, and 75.5% within 2 days. This high mortality rate has decreased because of the improvement of surgical therapy by introducing hypothermic circulatory arrest and antegrade cerebral perfusion.4 The occurrence of stroke is principally determined by patient-related and disease-related factors; however, use of cerebral perfusion can significantly reduce the occurrence of temporary neurologic dysfunction.5 An analysis of the international registry of acute aortic dissection showed that contemporary 1- and 3-year survival in patients with AADA treated surgically are excellent.6 Independent predictors of survival during the followup period do not appear to be influenced by in-hospital risks but rather by pre-existing co-morbidities. Therefore, the preclinical time from the very beginning of the symptoms until the start of the cardiothoracic surgical procedure might have an impact on the outcome of patients suffering AADA. This has not been addressed in previous studies. The aim of this investigation was to study whether secondary transfer to a level I cardiothoracic surgical center by helicopter emergency medical services (HEMS) is superior to ground emergency medical services (EMS) regarding long-term survival in Germany. In addition, we investigated the cost-effectiveness of HEMS and EMS. One has to acknowledge that we studied this preclinical situation in Germany, where both HEMS and EMS are equipped with a specially trained emergency physician at the scene, at least one paramedic, and a pilot in case of HEMS. The emergency physician at the scene is board-certified with special expertise in preclinical medicine, trauma, as well as intensive care medicine and intensive care interhospital transfer. Depending on the availability and immediacy of a given transport mode (HEMS or EMS), the emergency call dispatcher allocates an HEMS or EMS to the scene. In case of an interhospital transfer, the transferring hospital calls the emergency dispatcher, who seeks the fastest available Air Medical Journal 28:3
transportation vehicle to the transferring hospital. Typically, distances between 50 and 150 km are to be traveled in our geographic situation, which may not necessarily be the case in other geographic situations.
Methods Inclusion Criteria This study included all patients suffering an AADA surgery referred to Medical School Hannover with a complete HEMS or EMS transfer protocol (for either primary or secondary transfer) that are recorded and stored in the electronic data management system. This archive contains all clinical data of patients admitted since 1996.
Exclusion Criteria Exclusion criteria were all patients suffering aortic dissection Stanford type B despite complete HEMS or EMS transfer protocols, no existing HEMS/EMS protocol in aortic dissections type A, or no information of primary and secondary transportation. A total number of 365 patients suffering from AADA who were treated in the cardiothoracic and vascular department at Hannover Medical School in Germany were tested for eligibility. One hundred seventy-seven patients were eligible for inclusion in this study based on a complete HEMS or EMS transfer protocol. All of these 177 patients underwent emergency aortic surgery because of AADA between 1996 and 2005. The earliest surgery was performed in October 1987 and the latest in February 2005.
Data Collection • General parameters: Age at surgery, sex, date of death, date of hospital admission, distance of primary transfer, distance of secondary transfer, predispositions • Premedical parameters: Date and time of pain, localization and character of pain, unconsciousness, general complaints, place of rescue, recipient of emergency call • Transfer parameters for primary and secondary transport (see Definitions): Date and time of alarm, departure to patient, arrival at patient, handing over, departure to hospital, arrival at hospital, time of transfer, way of transportation (helicopter [HEMS] or ground based [EMS]), accompanying professionals, self-transportation, destination self- transportation, consciousness, Glasgow Coma Scale, systolic and diastolic blood pressure, pulse • Primary hospital: Arrival date, arrival time, symptoms, systolic blood pressure, diastolic blood pressure, pulse, diagnostics • Medical School Hannover: Arrival date, arrival time, diagnostics, motor disorder, blood pressure, pulse, anaesthesia, intubations, surgery date, surgery time, cross-clamp time, time on heart lung machine, time of cerebral perfusion, intensive care time, resuscitation, catecholamine May-June 2009
Follow-up Follow up was performed by direct telephone interview with the patients or relatives. Telephone calls were made to patients’ general practitioners, or a written questionnaire was mailed. The follow-up was 93% (166 cases) complete. End of research was August 1, 2006 (last interview). Mean time of follow-up was 1,881 ± 1,026 days (5 ± 23⁄4 years). Telephone interviews were done based on a standardized questionnaire. In case of death of the patient, a thorough analysis was done regarding date and detailed cause of death with the relatives.
Definitions • Acute aortic dissection type A: AADA was defined as acute because the pathologic condition took place within 0 to 14 days of surgery. An aortic dissection type A has a false lumen of the ascending aorta with or without aortic arch participation (DeBakey types I and II). • Mortality: Early mortality was defined as 30-day mortality. Overall mortality was mortality from date of aortic surgery to the end of the follow-up period. It includes mortality associated with cardiac diseases and mortality not associated with cardiac diseases. • Survival: Survival was defined as survival longer than a certain time t. Survival function represents the likelihood of living at time t of a given individual. • Mode of transport: Primary transport is transfer from the place of accident (scene) to the primary hospital (first hospital reached and approached during rescue). Primary transport is equivalent to rescue. Secondary transport is transfer from the primary hospital to the cardiothoracic surgical department (interhospital transfer). Paramedic transport is carried out by paramedics without an emergency doctor. Self-transport is not accompanied by any medical staff. • Costs: Costs of ground transport were separated into costs for doctor on call and emergency ambulance. An emergency doctor costs 315 for the first hour and 100 every additional hour. Emergency ambulance costs 228, including the first 20 km. Every additional kilometer costs 2.48. Helicopter transport costs 53 per helicopter minute in air, assumed that a helicopter travels at 3 km/min. Information on cost is based on personal communication with the responsible emergency dispatching center and the rescue organizations in the region of Hannover, Germany.
Patient Characteristics Age at AADA surgery was at mean 59 ± 13 years. The youngest patient recorded was 20 years old, and the oldest patient was 86 years old. One hundred fourteen patients (64%) were male, and 63 patients (36%) were female. Three percent (5/177) were transported primarily by HEMS and 24% (42/177) by EMS. In secondary transport, 25% (39/156 patients) had HEMS, and 58% (91/156 patients) had EMS transport. Patients` characteristics were divided into two groups of HEMS (group A) and EMS (group B) (Table 1). 147
Table 1. Patients’ characteristics as well as cardiothoracic surgical parameters for helicopter emergency medical service [HEMS; n=39] (Group A) and ground-based emergency medical service [EMS; n=91] (Group B). 2-tailed independent samples t-test showed no differences between HEMS and EMS HEMS (Group A) EMS (Group B) p value value Patients assessed value Patients assessed (A vs B) Age at surgery (years) 57±15 39/39 58±12 91/91 0.81 Number of peripheral vein catheters 2±1 23/39 2±1 33/91 0.71 Arterial catheter 1±0 5/39 1±0 2/91 Not performed Central venous catheter 1±0 11/39 1±0 13/91 Not performed Time of surgery (min) 256±65 39/39 278±110 91/91 0.24 Time cerebral perfusion (min) 23±15 39/39 26±11 91/91 0.35 Cross-clamp-time (min) 117±45 39/39 113±40 91/91 0.76 Time of intubation (min) 52±60 39/39 78±129 91/91 0.23 Resuscitation postsurgical No 33/39 No 84/91 0.69 Yes 6/39 Yes 7/91 Catecholamines postsurgical No 20/39 No 45/91 0.79 Yes 18/39 Yes 45/91 Days at intensive care unit 5±8 39/39 5±6 91/91 0.79
In 47 (27%) of 177 patients, primary transfers protocols could be analyzed. Twenty-one patients (12%) of 177 were directly transferred to Hannover Medical School (level I cardiothoracic and vascular surgery center) and 26 patients (15%) to regional hospitals. One-hundred-fiftysix patients (88%) had been transferred from a regional hospital to Hannover Medical School (level I cardiothoracic and vascular surgery center).
Statistical Analysis A P value less than .05 was considered statistically significant for all analyses. Survival functions were calculated and displayed by Kaplan-Meier curves. Modes of primary transport were analyzed by Pearson chi-square test. Modes of secondary transportation were analyzed by Kaplan-Meier survival curves compared using log-rank tests. Comparison of HEMS and EMS was done by twoFigure 1. Thirty-day mortality after AADA surgery, displayed by Kaplan-Meier curves.
tailed independent samples t-test. Distance of transportation and transfer times have been analyzed with regard to the survival by a Cox proportional hazard model, as well as the two-tailed independent samples t-test, also described by box-plots. Comparison of costs of primary and secondary transportation was done using the twotailed independent samples t-test and was described by box-plots. Statistical analysis was performed using SPSS 13 software (SPSS Inc., Chicago, IL).
Results Survival Rates Ninety-nine patients (56%) were alive at follow-up 3.5 years after AADA. Forty-six patients (26%) died during the first 30 days after surgery, and 21 patients (12%) died after the first 30 days postsurgery (Figs. 1, 2). Sixty-two patients (35%) died during the first year after surgery.
Mortality after Cardiothoracic Surgery Mortality after surgery was 2% (3/177) within the first hour, 5% (8/177) within 6 hours, 6% (10/177) within 12 hours, 11% (20/177) within 24 hours, 13% (23/177) within 48 hours, 14% (25/177) within 72 hours, and 26% (46/177) within 30 days after surgery. Twenty patients (11%) died of non–cardiac-associated reasons. Mean survival was 1,153 ± 1,124 (31⁄2 years ± 31⁄4).
Primary Transfer Type of Transfer: The choice of primary transport vehicle was not significant for survival (P = .78; Pearson chisquared). Independent samples t-test showed no significant difference in transportation distance of HEMS and EMS (P = .76). Cox proportional hazard model showed no significance for primary distances (30-day mortality, P = .545; overall mortality, P = .516). 148
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Figure 2. Overall mortality after AADA surgery, displayed by Kaplan-Meier curves.
way and return. Costs of HEMS were 836 ± 530 (5/157), based on 36 ± 26 km (5/157). Independent samples t-test showed no significant difference in costs of primary transportation between HEMS and EMS (P = 2.02).
Secondary Transfer
Figure 3. No significant difference in 30-day mortality (P = .5, logrank test) was seen between HEMS (n = 39) and EMS (n = 91), displayed by Kaplan-Meier curves.
Figure 4. No significant difference in overall mortality (P = .5, logrank test) was seen between HEMS (n = 39) and EMS (n = 91), displayed by Kaplan-Meier curves.
Type of Secondary Transfer: No significance was evident for secondary transfer by HEMS versus EMS regarding longterm mortality (P = 0.5) (Figs. 3, 4). Independent samples t-test showed no significant differences between HEMS and EMS, except the distance traveled during secondary transport (Tables 2–4). HEMS covered a distance of 110 ± 79 km and EMS a distance of 41 ± 57 (P = .01). Independent samples t-test showed a significant difference in transportation distance of HEMS in contrast to EMS in secondary transportation (P = 0.01) (Fig. 5). Cox proportional hazard model showed no significance of difference in transportation distance on mortality (30-day mortality, P = .623; overall mortality, P = .278). Independent samples t-test did not show any significant difference in transportation time of HEMS and EMS in secondary transportation (P = .76) (Fig. 6). Cox proportional hazard model showed no significance of difference in transportation time on mortality (30-day mortality, P = .9; overall mortality, P = .87). Time for alarm was analyzed in detail for secondary transport: • Time from alarm to arrival of secondary transport vehicle at primary hospital: HEMS (6/39) 66 ± 46 min; EMS (4/91) 48 ± 116 minutes • Time from alarm to patient´s arrival at Medical School Hannover: HEMS (6/39) 124 ± 63 minutes; EMS (6/91) 116 ± 98 minutes Costs of Secondary Transport: Secondary transfer costs in EMS were 497 ± 720 (82/156), calculated on 68 ± 78 minutes) emergency doctor time (81/156) and 137 ± 102 km emergency ambulance transport (82/156) one way and return. Secondary HEMS was 3,871 ± 2,790, based on 219 ± 158 km (39/156) one way and return. Independent samples t-test showed a significant difference in costs of secondary transportation (P = .01) (Fig. 7). HEMS secondary transfer for AADA was eight times more expensive than EMS.
Discussion
Costs of Primary Transport: Ground-based primary transport costs 296 ± 543 (33/157) based on 75 ± 96 minutes for doctor on call (26/157) and 25 ± 28 km for the emergency ambulance (33/157). Calculation was done with correction for self-transportation. Calculation of costs was done oneMay-June 2009
We hypothetized that survival among patients suffering from AADA is influenced by the mode of interhospital transportation (HEMS vs. EMS). Interestingly, we could not detect a significant difference between HEMS in contrast to EMS for interhospital transfer regarding either short-term or long-term mortality up to 3.5 years after cardiothoracic surgery. This result has to be discussed in relation to the current emergency service situation in Germany. A board-certified emergency physician with special expertise in preclinicial medicine, trauma management, and interhospital transfer medicine is provided on both ground-based EMS and 149
Table 2. Time course from AADA symptoms to AADA surgery in a level-I cardiothoracic department for patients transferred by either helicopter emergency medical service [HEMS; n=39] (Group A) or emergency medical service [EMS; n=91] (Group B). 2tailed independent samples t-test showed significant differences between HEMS and EMS for secondary transfer distance (p=0.01). HEMS (Group A) EMS (Group B) p value value (n=39) value (n=91) (A vs B) Symptoms to primary hospital (min) 115±117 26/39 104±129 28/91 0.78 Time at primary hospital (min) 1587±2447 38/39 2088±2907 50/91 0.38 Time from alarm to arrival of secondary vehicle (min) 66±46 6/39 48±49 4/91 0.58 Time of secondary transfer (min) 39±19 39/39 37±42 91/91 0.77 Distance of secondary transfer (km) 110±79 39/39 41±57 91/91 0.01 Presurgery time at cardiothoracic surgery center (min) 520±1246 39/39 551± 1521 91/91 0.92
Table 3. AADA patients’ mental and physical status at primary transport by helicopter emergency medical service [HEMS; n=5] (Group A) or emergency medical service [EMS; n=42] (Group B). 2-tailed independent samples t-test showed no differences between HEMS and EMS. HEMS (Group A) EMS (Group B) p value value (n=5) value (n=42) (A vs B) Consciousness evident 5/5 evident 26/42 0.33 Lost 0/5 Lost 5/42 Glasgow Coma Scale 15±1 5/5 12±4 19/42 0.22 Systolic blood pressure (mmHg) 110±31 5/5 130±49 20/42 0.31 Diastolic blood pressure (mmHg) 60±18 4/5 73±16 11/42 0.26 Pulse 65±18 5/5 69±24 22/42 0.68 Motor disorders No 3/5 (15%) No 27/42 (64%) 0.13 Yes 2/5 (40%) Yes 4/42 (10%) Preclinical intubation/mechanical No 5/5 (100%) No 29/42 (70%) 0.56 ventilation Yes 0/5 Yes 2/42 (5%) Preclincial resuscitation No 5/5 (100%) No 30/42 (71%) 0.68 Yes 0/5 Yes 1/42 (1%) Catecholamines preclincal No 5/5 (100%) No 30/42 (71%) 0.68 Yes 0/5 Yes 1/42 (1%)
HEMS services. All 76 emergency helicopters throughout Germany are staffed with one emergency physician and at least one or two flight nurses. Furthermore, interhospital transfer of critical ill patients is feasible using a mobile intensive care unit, which is equipped with advanced respiratory and hemodynamic support facilities. We thought that the HEMS service might be superior to ground-based EMS, especially regarding the time of transfer. However, the transfer times were not significantly different despite the twofold longer distance traveled by HEMS versus EMS interhospital transfer. Thus, longer distances were traveled using HEMS versus EMS in the same time. The strength of this study is the currently largest patient cohort analyzed with a complete interhospital transfer protocol and the detailed perioperative and postoperative documentation. The follow-up was 93%, with 1,881 ± 1,026 days (5 ± 23⁄4 years). Based on the intrahospital, the 30-days, and 150
the long-term survival rates, we thought it would be appropriate to determine the effect size of the mode of transportation as the primary endpoint. Although survival among patients suffering AADA is multifactorial, time has been consistently identified as a crucial factor. Given the aforementioned report in acute aortic dissection type A, each hour until the cardiac operation will increase mortality by 1%. Currently there is no comparable published study determining the impact of the mode of preclinical or interhospital transportation among patients suffering from AADA. Stone et al7 found no difference of HEMS versus EMS interhospital transport among cardiac patients with unstable angina or myocardial infarction. Mitchell and Tallon8 analyzed a cohort of 34 patients suffering suspected aortic emergencies transferred by HEMS only. Boyd et al9 described a benefit of interhospital HEMS transport on trauma patients’ survival. Comparing HEMS Air Medical Journal 28:3
Table 4. AADA patients’ mental and physical status at secondary transport by helicopter medical service [HEMS; n=39] (Group A) or emergency medical service [EMS; n=91] (Group B). 2-tailed independent samples t-test showed no differences between HEMS and EMS. Parameters during secondary HEMS (Group A) EMS (Group B) p value transport (interhospital transfer) value (n=39) value (n=91) (A vs B) Consciousness evident 26/39 (67%) evident 38/91 (42%) 0.61 Lost 13/39 (33%) Lost 15/91 (16%) Glasgow Coma Scale 11±5 33/39 11±6 39/91 0.91 Systolic blood pressure (mmHg) 123±27 32/39 124±31 46/91 0.95 Diastolic blood pressure (mmHg) 70±20 28/39 70±16 35/91 0.93 Pulse 86±22 31/39 85±23 46/91 0.87 Motor disorders No 36/39 (92%) No 49/91 (54%) 0.97 Yes 3/39 (7%) Yes 4/91(4%) Interhospital intubation/mechanical No 29/39 (74%) No 39/91 (43%) 0.93 ventilation Yes 10/39 (26%) Yes 14/91 (15%) Interhospital resuscitation No 39/39 (100%) No 52/91 (57%) 0.39 Yes 0/39 Yes 1/91(1%) Interhospital catecholamines No 35/39 (90%) No 45/91 (49%) 0.49 Yes 4/39 (10%) Yes 8/91(9%)
versus EMS with regard to primary rescue, a broader number of studies have been published focusing on trauma patients. However, the role of HEMS in primary trauma transfer remains controversial regarding mortality. Whereas some, such as Cunningham et al,10 Fühler,11 and Biewener et al,12 found no confirmation of a better survival on HEMStransported patients, others, such as Frink et al13 and Mitchell et al,14 identified benefit on survival for HEMS rescue. Di Bartolomeo et al,15 who analyzed traumatic cardiac arrest, showed no significant benefit for HEMS in contrast to EMS. Conversely, HEMS transfer for patients suffering stroke seemed superior to ground-based EMS. Therefore, distinct clinical entities might exert a differential pattern regarding the outcome based on mode of transportation. It
has to be clearly pointed out that our preclinical and clinical situation with a dense network of HEMS and EMS with a huge overlap as well as no real remote areas might be somewhat different from some areas in northern America. Although HEMS traveled a distance more than twice as far as ground-based EMS for interhospital transfer (P = .01), this difference of distance was not significant regarding mortality because the time was the same. It is current practice that distance is a criterion for putting HEMS into action, at least in Germany. However, we found no significant difference between HEMS and EMS in secondary transfer time. Time from alarm for HEMS at primary hospital until arrival at primary hospital (66 minutes) and Medical School Hannover (124 minutes) was longer
Figure 5. HEMS (n = 39) traveled more than twofold longer secondary transport (interhospital) distances (P = .01; two-tailed independent samples t-test) than ground-based EMS (n = 115), displayed by box-plot.
Figure 6. No significant differences in secondary transport time (P = .76, two-tailed independent samples t-test) between HEMS (n = 39) and EMS (n = 74), displayed by box-plot.
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Figure 7. HEMS (n = 39) was eightfold more expensive (P = .01; two-tailed independent samples t-test) than EMS (n = 82), displayed by box-plot.
cohort of 177 patients suffering from AADA transferred to a single cardiothoracic center is the largest study to date, the patient cohort is still small in contrast, for example, to patients suffering from acute myocardial infarction. Acute aortic dissection type A is not a common diagnosis of chest pain. We performed a retrospective chart analysis with a prospective follow-up. A prospective randomized trial to compare EMS with HEMS might be a superior study design; however, this is limited in practice by a number of factors. We thought to standardize the study as much as possible by having a single cardiothoracic department perform all of the aortic surgery procedures. However, several distinct cardiac surgeons performed the procedures, which might confound the mortality rates as well.
Conclusions
than for EMS (48 minutes primary hospital/115 minutes Medical School Hannover). Nicholl17 analyzed activation time, response time, and on-scene time for HEMS, which was longer on average than for ground transport, but mostly depending on longer distances. Also, Ringburg18 described longer times for HEMS; however, when corrected for severity of trauma and patient characteristics, no influence on mortality of trauma patients could be seen. Frink et al13 showed no influence of longer HEMS rescue times on mortality of polytraumatized patients, in contrast to ground-based EMS. Besides mortality rates, we were interested in the calculated costs of either HEMS or EMS interhospital transfer. HEMS (3,871) was eightfold more expensive than EMS (497) for interhospital transfer of AADA patients. This is in line with Nicholl et al,17 calculating costs of HEMS as 595 pounds and EMS as 97 pounds. In 1997, Gearhart et al19 applied a cost-effectiveness analysis from the service provider’s perspective to cost and effectiveness estimates of HEMS for trauma patients. The effectiveness estimates were calculated with the trauma injury severity score (TRISS) methodology from literature sources and data from a cohort of patients transported by helicopter during 1994 and 1995. Transport costs were $2,214 per patient, and each additional survivor's hospitalization averaged $15,883. For the base case (five additional survivors per 100 patients flown), cost per life was $60,163, and discounted cost per year of life was $2,454. The authors assumed that helicopter air medical transport provides a substantial survival benefit for trauma patients, suggesting that this service is a cost-effective option for the treatment of trauma patients. However, these costs were calculated 12 years ago and do not necessarily correspond to various emergency medical systems over the world.
Limitations When interpreting our data, several limitations have to be taken into account. Despite the fact that the presented 152
We found no advantage of survival rates among patients suffering AADA transferred by either HEMS or EMS in primary or secondary transport. Although HEMS traveled a distance more than twofold longer than ground-based EMS at the same mission time, HEMS was eightfold more expensive than ground-based EMS in AADA.
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16. Conroy MB, Rodriguez SU, Kimmel SE, Kasner SE. Helicopter transfer offers a potential benefit to patients with acute stroke. Stroke 1999;30:2580-4. 17. Nicholl JP, Beeby NR, Brazier JE. A comparison of the costs and performance of an emergency helicopter and land ambulances in a rural area. Injury 1994;25:145-53. 18. Ringburg AN, Spanjersberg WR, Frankema SP, Steyerberg EW, Patka P, Schipper IB. Helicopter emergency medical services (HEMS): impact on on-scene times. J Trauma 2007;63:258-62. 19. Gearhart PA, Wuerz R, Localio AR. Cost-effectiveness analysis of helicopter EMS for trauma patients. Ann Emerg Med 1997;30:500-6.
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