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Resuscitative Endovascular Balloon Occlusion of the Aorta: A Gap Analysis of Severely Injured UK Combat Casualties

Morrison, Jonathan J.*†; Ross, James D.; Rasmussen, Todd E.§∥; Midwinter, Mark J.†¶; Jansen, Jan O.**††‡‡

doi: 10.1097/SHK.0000000000000136
Clinical Aspects
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ABSTRACT The control of torso and junctional zone bleeding in combat casualties is particularly challenging because of its noncompressible nature. Resuscitative endovascular balloon occlusion of the aorta (REBOA) has demonstrated promise in translational large animal and early clinical series as an effective resuscitation and hemorrhage control adjunct. However, it is unknown what proportion of combat casualties has an injury pattern and clinical course that is amenable to REBOA deployment. The prospective UK Joint Theatre Trauma Registry was used to retrospectively identify all UK military personnel who has sustained a severe combat injury, defined as an Abbreviated Injury Scale of three or greater, in the course of 10 years. Patients were then divided into three groups based on Abbreviated Injury Scale injury pattern: no indications for REBOA, contraindications (mediastinal, cervical, and axillary hemorrhage), and indications (torso and pelvic hemorrhage). From a total of 1,317 patients, 925 (70.2%) had no indication, 148 (11.2%) had a contraindication, and 244 (18.5%) had an indication for REBOA. Within the group with indications for REBOA, there were 174 deaths: 79 at the point of wounding, 66 en route to hospital, and 29 in-hospital deaths. The median (interquartile range) time to death in patients dying en route was 75 (42–109) min, and the median prehospital time for casualties admitted to hospital was 61 (34–89) min. One-in-five severely injured UK combat casualties have a focus of hemorrhage in the abdomen or pelvic junctional region potentially amenable to REBOA deployment. The UK military should explore REBOA as a potential en route hemorrhage control and resuscitation adjunct.

*Academic Unit of Surgery, Glasgow Royal Infirmary, Glasgow; and The Academic Department of Military Surgery & Trauma, Royal Centre for Defence Medicine, Birmingham, UK; 59th Medical Wing, Lackland Air Force Base (San Antonio), Texas; §The Norman M. Rich Department of Surgery, The Uniformed Services University of the Health Sciences, Bethesda; and US Combat Casualty Care Research Program, Fort Detrick, Maryland; and National Institute of Health Research, Surgical Reconstruction and Microbiology Research Centre, Queen Elizabeth Hospital, Birmingham; **144 Parachute Medical Squadron, 16 (Air Assault) Medical Regiment; and ††Aberdeen Royal Infirmary and ‡‡NHS Research Scotland, HSRU, Aberdeen, UK

Received 1 Dec 2013; first review completed 20 Dec 2013; accepted in final form 7 Jan 2014

Address reprint requests to Jonathan J. Morrison, MRCS, The Academic Department of Military Surgery & Trauma, Royal Centre for Defence Medicine, Birmingham Research Park, Vincent Drive, Edgbaston, Birmingham, B15 2SQ, UK E-mail: jjmorrison@outlook.com.

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INTRODUCTION

Hemorrhage is the leading cause of potentially preventable death following both civilian and military traumas (1, 2). The last decade of war in Iraq and Afghanistan has seen significant innovation in the management of compressible hemorrhage—extremity bleeding amenable to control by simple pressure—which has translated to improved survival (3). However, bleeding from noncompressible sites within the torso and junctional regions (groin and axilla) remains a significant cause of mortality (4–6).

A recent review of 10 years of US military deaths identified 24.3% of casualties as having a potentially survivable injury, of which 90.9% were due to hemorrhage (1). The largest focus was truncal (67.3%) followed by junctional (19.2%) and extremity (13.5%) sources. Importantly, nine out of 10 deaths occurred before admission to a medical treatment facility (MTF). There is a pressing need for a hemorrhage control and resuscitation adjunct that can be deployed before MTF admission to sustain life until definitive hemorrhage control can be attained.

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a technique that has demonstrated promise in both large animal and early clinical case series, as an adjunct that supports central perfusion and controls arterial inflow (7–10). Two functional aortic zones of occlusion have been described: thoracic (zone I) and infrarenal (zone III), for exsanguinating abdominal and pelvic hemorrhage, respectively (7).

However, despite compelling evidence demonstrating the favorable hemodynamic profile of aortic occlusion in hemorrhage, it is unknown what proportion of combat casualties have an injury pattern and clinical course that would be amenable to REBOA deployment. The aim of this study was to evaluate 10 years of consecutive UK combat casualties to identify patients that might have benefitted from REBOA.

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METHODS

This study was conducted following approval from the Royal Centre for Defence Medicine Academic Unit. The prospectively collected UK Joint Theatre Trauma Registry (JTTR) was used to retrospectively identify all UK military personnel sustaining a severe combat injury in one or more body region, in Iraq or Afghanistan, between August 2002 through July 2012. Severe injury was defined as a military Abbreviated Injury Scale (AIS) score of three or greater in any AIS body region. The 2005 military AIS scores were used to calculate both the Injury Severity Score (ISS) and the New Injury Severity Score (NISS).

The UK JTTR is a performance improvement tool that captures data on all casualties admitted to UK MTFs. It is most detailed in the case of UK military personnel, as the JTTR has visibility of this population from the point of wounding to either discharge or postmortem examination. Importantly, the JTTR includes data pertaining to casualties who do not survive to MTF admission, permitting the comprehensive analysis of a consecutive population of wartime injured.

Suitability for REBOA was initially determined by injury pattern using AIS coding. Three categories were defined: indicated, contraindicated, and not indicated (Table 1). In general terms, zone I REBOA was deemed indicated in the setting of abdominal hemorrhage: high grade (AIS ≥4) solid organ, mesenteric disruption, or injury to a named vessel proximal to the aortic bifurcation. Zone III REBOA was deemed indicated in pelvic/groin hemorrhage: pelvic fracture with ring disruption, traumatic amputation at/near the hip, or injury to a named vessel proximal to the femoral segments.

Table 1

Table 1

Contraindication to REBOA was defined as a focus of noncompressible hemorrhage proximal to the zone of occlusion. This included thoracic aortic disruption, and arterial injury located within the superior mediastinum, neck, and axillary regions. Patients with both an indication and contraindication for REBOA were included only in the contraindicated group, and patients with neither were placed in the no-indication group.

Patients with an injury pattern indication for REBOA then underwent a detailed review of their registry record including examination of prehospital and in-hospital free-text description fields. This enabled the identification of patients who had signs of life (SOLs) at the point of wounding, but lost cardiac output en route to an MTF. This is important, as the purpose of this study was to identify a population where REBOA has a realistic window of opportunity for deployment. Patients with catastrophic wounding and cardiac arrest at the point of wounding will not benefit from REBOA. Categorization of SOL was deliberately conservative; in the absence of documentation to that effect, patients were assumed to have died at the point of wounding.

The operative indications for patients undergoing thoracotomy and laparotomy were also retrieved. Thoracotomy indications were divided into three categories: thoracic hemorrhage control (control of bleeding vessels, lung parenchyma), nonhemorrhage control (control of air leaks, release of tamponade), and resuscitation (aortic cross clamping, cardiac massage). Laparotomy indications were similarly classified: abdominal hemorrhage control (packing, organ removal), nonhemorrhage control (management of hollow organ injury), and proximal control (control of lower-extremity inflow via the abdomen).

This permits not only an analysis of types of surgical maneuvers required, but also the identification of a population of patients who required only arterial control in isolation. For example, patients with very proximal traumatic amputations can require a laparotomy to obtain vascular inflow control of the iliac arteries, but no other abdominal intervention. The intraoperative use of REBOA may have a role in avoiding cavity surgery for isolated arterial control (11).

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RESULTS

During the decade of war between August 2002 through July 2012, there were a total of 1,317 UK military personnel who sustained one or more severe combat injury and were entered into the UK JTTR (Fig. 1). This was associated with a high burden of injury as indicated by a mean ISS of 40 (SD, 27) and a mortality rate of 43.2%. In terms of injury pattern, 925 patients (70.2%) had no indication for REBOA, 148 (11.2%) had a contraindication, and 244 (18.5%) had an injury pattern that might have been amenable to REBOA.

Fig. 1

Fig. 1

Of the 244 with an injury pattern indication for REBOA, 145 patients (59.4%) died before MTF admission: 79 patients were considered to have died at the point of wounding, and 66 died en route to an MTF. Of the 99 admitted to an MTF, 29 patients subsequently died of their injuries, with 70 survivors. The indicated zone of occlusion was consistent across these four groups (P = 0.791), with zone I indicated in 147 (60.2%) and zone III in 97 (39.8%) of the cohort (Fig. 2). Only the patients who survived beyond the point of wounding (n = 165) will be analyzed further and are considered in three groups: en route deaths, MTF deaths, and survivors.

Fig. 2

Fig. 2

The sex, age, and mechanism of injury were consistent across en route deaths, MTF deaths, and survivors (Table 2). The cohort could be characterized as largely male, in their mid-20s, predominantly injured by an explosive event. As per the selection criteria, there was a high preponderance of abdominal and lower-extremity injuries across all three groups. There was a stepwise increase in injury burden across the groups as measured by both ISS and NISS (P < 0.001). Patients who died en route to an MTF had the greatest injury burden, followed by MTF deaths, with survivors sustaining the lowest injury burden. This pattern was mirrored when considering anatomical injury pattern with patients dying en route sustaining a significantly greater proportion of severe head and chest injuries compared with the other groups.

Table 2

Table 2

Of the 66 patients who died en route to an MTF, reliable time of death was recorded in 36 patients (54.5%) with median (interquartile range [IQR]) time of 75 (42–109) min. While all patients had a focus of noncompressible hemorrhage, traumatic brain injury (TBI) was felt to be the greater contributor to mortality in 19 patients (28.8%).

Of the 99 patients who survived to MTF admission (i.e., MTF deaths and survivors), prehospital time was available in 57 (57.6%) of cases, with a median (IQR) time of 61 (34–89) min. Medical treatment facility deaths had a lower admission systolic blood pressure, pulse rate, and Glasgow Coma Scale score compared with survivors (Table 3). Of the 29 MTF deaths, all had a focus of hemorrhage, but the primary cause of death was noncompressible hemorrhage in 14 (48.3%), TBI in nine (31.0%), and multiple organ failure in six (20.7%).

Table 3

Table 3

The use of thoracotomy, laparotomy, and pelvic fixation for hemorrhage control was used similarly between fatalities and survivors (Table 3). However, resuscitative thoracotomy was used in a greater proportion of fatalities (52.2% vs. 8.3%; P < 0.001). Interestingly, within the 70 survivors, four (8.3%) required a thoracotomy, and eight (11.4%) required a laparotomy for aortic/iliac control in isolation; that is, no other thoracic or abdominal intervention was required.

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DISCUSSION

This study is the first to examine a consecutive population of wartime wounded to evaluate the potential role of REBOA as a hemorrhage control and resuscitative adjunct. The current study demonstrates that one in five patients sustaining a severe injury had an injury pattern that is potentially amenable to this maneuver, although 79 (32.3%) had no SOL at the scene, and REBOA is unlikely to change their outcome. However, 89 patients (36.5%) had a spontaneous circulation that deteriorated into circulatory arrest before or upon MTF admission. Resuscitative endovascular balloon occlusion of the aorta may have utility in this group, by sustaining central perfusion until definitive hemorrhage control can be attained.

Patients with critical bleeding require concomitant resuscitation and hemorrhage control (12). The last decade has seen significant advances in the field of resuscitation, with formalized damage control resuscitation algorithms capable of correcting even profound physiological abnormality intraoperatively (13). This has resulted in the lowest died-of-wounds rate in contemporary conflict (14); however, this is dependent on a casualty surviving to an MTF, and it is now well established that the majority of deaths occur before admission (1, 4, 5).

The fundamental problem is how to get an exsanguinating patient to definitive hemorrhage control before they undergo a circulatory arrest. Definitive hemorrhage control is generally achieved using either operative or angioembolic techniques (15). This requires trained personnel working with well-maintained infrastructure support by an appropriate logistical chain and as such is only really practical in a formal MTF. Clearly one solution is to move the MTF closer to the point of wounding; however, this is rarely practical in dynamic and kinetic military operations. An alternative solution is the deployment of an adjunct that can support the spontaneous circulation until definitive hemorrhage control.

Aortic balloon occlusion, as achieved by REBOA, results in a hemodynamic profile, which is highly beneficial to trauma patients as demonstrated in both animal (8, 16) and human studies (10). First, provided the hemorrhagic focus is perfused distal to the balloon, inflation will control arterial inflow slowing the rate of exsanguination. Second, the increase in afterload will enhance both myocardial and cerebral perfusion. This may be of particular importance in the setting of TBI where the maintenance of cerebral perfusion helps to reduce secondary brain injury. The current study reports that approximately a third of patients had sustained a TBI in addition to their hemorrhagic focus. However, this neuroprotective effect is strictly theoretical, and currently there is no supporting human evidence.

Furthermore, REBOA may have a role as a surgical adjunct by reducing the need for cavity surgery in patients requiring arterial control in isolation. The current study demonstrates that of the 70 patients who survived, 14 required a laparotomy or thoracotomy purely for proximal control of the aorta or iliac segments. The operating room use of REBOA could have theoretically eliminated the need for open surgery, reducing the associated physiological penalty. This has the greatest potential for patients sustaining a dismounted complex blast injury where the control of pelvic and proximal extremity hemorrhage often necessitates a laparotomy (11, 17).

Although the concept of REBOA may appear attractive, it is important to acknowledge the practical challenges involved in the deployment of this adjunct, especially in the pre-MTF setting. The main issues relate to obtaining arterial access and the “blind” insertion of a catheter system without fluoroscopic assistance. Arterial access in hypotensive patients is challenging, and this step has limited the effectiveness of aortic balloon occlusion in the historic literature (18). However, with the refinement of endovascular technology and the availability of portable ultrasound imaging devices, the chances of successful arterial cannulation can be optimized (10).

Furthermore, the risks of blind insertion are also being minimized with a number of technical innovations combined with an improved understanding of aortic morphometry. Novel REBOA systems have been designed that combine a low-profile, unibody construction with self-centering capability to maintain aortic travel (19). Computed tomography–based morphometric analysis has permitted the characterization of the internal-external relationship between the aorta and torso height (20, 21). This has enabled the development of equations that can reliably predict the insertion length required to occlude the desired aortic zone (21).

With these challenges in mind, the deployment of a REBOA system is really practical only during the en route phase of evacuation, where care can be delivered in a more permissive environment. Advanced medical retrieval (AMR) platforms such as the UK Medical Emergency Response Team and the USAF Tactical Critical Care Evacuation Team are ideally placed to deploy REBOA (22, 23).

These platforms already deliver a suite of advanced interventions such as drug-assisted intubation, central venous access, and the administration of blood products (22). Importantly, the skill set required to perform these interventions is similar to those required to deploy a REBOA catheter. Clinicians need to be familiar and well practiced with Seldinger vascular access techniques and the use of invasive monitoring. These practical skills need to be combined with prompt injury pattern recognition and decisive decision making (10).

Furthermore, the current study reports a median (IQR) time to death in patients with SOLs en route, who die before MTF admission of 75 (42–109) min. This, theoretically, may be a long-enough window in which an AMR platform could retrieve a patient and deploy a REBOA system en route to an MTF and definitive hemorrhage control.

The current study has a number of important limitations that require discussion. The most important caveat is that the reported analysis is strictly theoretical. The reality is that the majority of patients who die before MTF admission have sustained a high burden of injury and that, even with immediate operative intervention and resuscitation, salvage is not ensured.

Furthermore, the current study does not report comprehensive time-of-death data, and it is unknown if the window for REBOA deployment is actually shorter than reported. However, within the deployed experience of the authors, these figures are not incongruous.

It is also important not to overstate the case for REBOA as other mechanical adjuncts for resuscitation and hemorrhage control have come and gone. Pneumatic antishock garments is such an example that generated much interest through the 1970s and 1980s, but ultimately, there has been no demonstrable reduction in mortality, length of stay hospital, or ICU stay (24). A key difference with REBOA is that it combines both hemorrhage control and resuscitation, setting it apart from many other mechanical adjuncts. With these points in mind, the current study makes a compelling case for the pre-MTF deployment of REBOA in torso and pelvic hemorrhage.

In conclusion, one in five severely injured UK combat casualties has a focus of hemorrhage in the abdomen or pelvic junctional region. This is associated with a high burden of mortality, and there exists a discreet and definable group of patients that undergo exsanguination en route to an MTF. These patients would theoretically benefit from the deployment of a REBOA system, ideally onboard an AMR platform that is clinically well supported. The UK Defence Medical Service should explore the use of REBOA during the en route phase of care for patients with evidence of noncompressible hemorrhage that are at risk of exsanguinating before definitive hemorrhage control.

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ACKNOWLEDGMENTS

The authors thank the staff at the UK JTTR, Royal Centre for Defence Medicine, Birmingham, United Kingdom, for providing the data for analysis.

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Keywords:

Hemorrhage control; trauma; military surgery; REBOA; Resuscitative endovascular balloon occlusion of the aorta; resuscitation

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