Article Text
Abstract
Developments in military personal armour have aimed to achieve a balance between anatomical coverage, protection and mobility. When death is likely to occur within 60 min of injury to anatomical structures without damage control surgery, then these anatomical structures are defined as ‘essential’. However, the medical terminology used to describe coverage is challenging to convey in a Systems Requirements Document (SRD) for acquisition of new armour and to ultimately translate to the correct sizing and fitting of personal armour. Many of those with Ministry of Defence responsible for the procurement of personal armour and thereby using SRDs will likely have limited medical knowledge; therefore, the potentially complex medical terminology used to describe the anatomical boundaries must be translated into easily recognisable and measurable external landmarks. We now propose a complementary classification for ballistic protection coverage, termed threshold and objective, based on the feasibility of haemorrhage control within the prehospital environment.
- cardiothoracic surgery
- orthopaedic & trauma surgery
- thoracic surgery
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Introduction
Attempts at prevention of war injury through the use of personal armour has been documented for millennia. Warriors depicted on the Stele of Vultures, an ancient monument commemorating a battle c.4000 years ago, can be seen wearing war helmets with rudimentary facial protection.1 Body armour is defined as a type of personal protective equipment worn by military personnel designed to prevent or reduce injury from ballistic projectiles penetrating structures within the thorax and abdomen.2 The current body armour worn by UK Armed Forces personnel is the VIRTUS personal armour and load carriage system3 and comprises soft and hard elements (Figure 1). The soft element is in the form of a vest manufactured from high-performance fibres, providing protection against low-velocity fragments and protection from high-velocity rifle bullets is provided by ceramic-faced, composite-backed hard armour plates.
To optimise the design of body armour, the anatomical structures requiring coverage need to be articulated. These are medical judgements taking into account, for example, likely distance from a medical facility and the types of threats requiring mitigation. Coverage can then be modified by means of a risk-based analysis that includes human factor considerations, such as comfort, fit, equipment integration and interoperability.2 In recent years, there has been a paradigm shift in how armour design has been developed and optimised with a significant increase in clinical input based on injury analysis.4 In 2015/2016, clinicians, scientists and mathematical modellers working for different parts of the UK Ministry of Defence (MoD) collaborated to achieve multidisciplinary consensus on those ‘essential’ and ‘desirable’ anatomical structures within the torso (Table 1).2 Here we propose an additional complementary classification of coverage, termed threshold and objective, and their application to coverage of the torso. The aim of these additional descriptions is to assist with the definition of future personal armour by linking internal anatomy to external surface landmarks and anthropometric data. This will be a key element of the risk-based analysis to ensure personal armour provides the optimum anatomical coverage across the full range of armour sizes necessary for the UK Armed Forces population.
Essential and desirable medical coverage
The torso is considered a single anatomical area that comprises the thorax and abdomen.2 In an analysis of a cohort of >700 UK service personnel with battlefield gunshot injuries during Iraq and Afghanistan, the overall mortality rate was 24%. After head injury, trauma to the torso was the second most common cause of death on the battlefield.5
For UK Armed Forces personnel, the required area of coverage of personal armour for the torso was redefined in 2016 based on medical analysis of injury patterns, using the terms essential and desirable 2 (Table 1). This classification enabled the first objective comparisons of the coverage provided to the essential and desirable structures by personal armour using the Coverage of Armour Tool. The aim was to define the area of coverage of personal armour based on clinical evidence only, and to be independent of the materials technology available. Area of coverage could subsequently be modified to meet other system requirements such as level of protection (to match severity of threat), mobility, equipment integration, interoperability, comfort and acceptable thermal burden.6
Anatomical structures were defined as essential or desirable based on evidence as to the likelihood of death after injury. Essential structures were those deemed likely to result in death within 60 min of significant injury unless damage control surgery (DCS) could be achieved within this time. This was representative of the clinical timelines seen in recent conflicts in Afghanistan specifically.7 Desirable structures were of three types: (1) those which if injured would lead to death outside 60 min from injury, (2) those in which it was recognised that injury may cause life-changing morbidity and (3) those for which rehabilitation is particularly challenging.2 We believe that defining structures in relation to the time to DCS and not just ‘time to medical care’, as used in the past, is an important differentiation because surgical intervention is the only means of achieving definitive control of non-compressible torso haemorrhage (NCTH). At the time of the published consensus in 2016, the thoracic component of the trachea was not included as being essential due to a lack of published evidence to directly support its inclusion. However, our group believes that the intrathoracic part of the trachea (before it bifurcates into the main bronchi) should be included as it is not amenable to prehospital cricothyroidotomy, as is the cervical part of the trachea.
Future developments in clinical treatments may allow extension of the time to DCS. For example, novel haemostatic agents such as intra-abdominal foam8 9 and endovascular or extravascular occlusion of aortic blood flow10 are under investigation as temporary methods of control of NCTH.11 At present, these techniques are not widely available in UK military practice. Even if potential benefits are realised, these bridging measures only allow extension of the time to DCS and do not replace the need for surgery. Similarly, a recent systematic review has demonstrated the benefit of administering prehospital plasma on patient survival in mature civilian trauma systems.12 The effect of prehospital blood product transfusion on extending the window to DCS has validity but has not yet been explicitly demonstrated.
A new proposal: threshold and objective coverage
Medical analysis has successfully identified which anatomical structures need to be protected to reduce the consequences of combat injury (secondary prevention). However, it has been challenging to convey how a particular internal anatomical structure relates to external landmarks and to translate this to personal armour coverage requirements in Systems Requirements Documents (SRDs) for future acquisition. Those using SRDs will likely have limited medical knowledge, and therefore the medical terminology used to describe the anatomical boundaries must be translated into easily recognisable and measurable external landmarks (Table 2).
The terms threshold and objective are terms already widely used within SRDs in Defence Acquisition as described in Joint Service Publication (JSP) 65513 and Knowledge in Defence (KiD).14 JSP 655 is the policy and guidance on MoD investment approvals and scrutiny. KiD defines how the MoD conducts, governs and controls the Defence acquisition process and is the primary bearer of all policy and guidance governing Defence’s project delivery and commercial functions. While the definitions of essential and desirable coverage refer to internal anatomical structures,2 our threshold and objective coverage definitions uses the corresponding surface landmarks,15 and further classifies according to the feasibility of haemorrhage control within the prehospital environment. Therefore, to maintain consistency with Defence acquisition nomenclature in SRDs, ‘threshold’ coverage is the absolute minimum area/size that must be afforded coverage by personal armour. Less than the threshold would not be considered to provide an improvement over current capabilities and is not medically recommended. ‘Objective’ coverage is what armour should aspire to achieve. For personal armour coverage, objective coverage should encompass the additional area(s) to be covered as far as practicably possible as this could significantly increase operational utility (eg, increase the time to DCS) and mitigate the risk of death in 60 min or less if injured, but while also not impeding mobility, weight and thermal burden. At present, Objective coverage is an aspiration for future innovation in both personal armour materials as well as clinical treatment. The threshold and objective measures of personal armour coverage aim to provide clearer definitions of the coverage required to provide optimum protection in the future battlespace, based on underpinning medical understanding and research.
Applying the principles of threshold and objective coverage to the torso
The boundaries of those anatomical structures requiring ‘essential’ coverage from projectiles directed toward the front of the torso can be defined by three external landmarks (Figure 2). Analysis of CT scans has demonstrated that all the ‘essential’ anatomical components are within the thorax (ie, bounded by the ribcage) with the exception of the abdominal portion of the aorta.15 Medical coverage for projectiles directed toward the rear of the torso should be a mirror image of that directed from the front; therefore, additional external landmarks for the rear are not recommended.
Vertical measurements of the torso
The three vertical landmarks for determining the vertical measurements of torso coverage are the suprasternal notch (SSN), lower border of the ribcage and the iliac crest. Bleeding structures within the ribcage are inaccessible to most prehospital medical provision and therefore bleeding cannot be stopped until advanced medical care is reached (Table 2). Ongoing haemorrhage from the thorax requires thoracotomy, with poor survival in the military environment.16 17 In an observational study of 65 consecutive patients undergoing resuscitative thoracotomy following wartime injury, the observed survival rate was 22%.18 This means that the threshold coverage must include the majority of the ribcage, that is, from SSN to lower border of ribcage. Exsanguinating haemorrhage in the abdomen or pelvis could, in future, potentially be controlled by occlusion of the abdominal part of the aorta,19 so would be considered within the objective coverage area (Figure 1). We note that external aortic compression through the use of a the abdominal aortic and junctional tourniquet benefits only a very small proportion of injuries,20 and that the role of injected intracavitary self-expanding foam or resuscitative endoluminal balloon occlusion of the aorta (REBOA) in the prehospital military environment remains uncertain.20 21 However, the technique of REBOA continues to develop and is being rapidly adopted by many prehospital teams,22 and we therefore believe it should be considered within the framework of objective coverage.
Horizontal measurements of the torso
Currently soft armour covers the whole width of the torso, using the external landmarks of the acromion processes as the most lateral extent superiorly. In contrast, the hard armour plate requires cut-out areas to ensure movement of the shoulders (Figure 3). Therefore, the ‘superior width’ of threshold coverage should be related to the width of the vascular components of the mediastinum (heart and aorta), and the ‘inferior width’ must cover the liver and spleen. For threshold coverage, the superior width should be asymmetrical to the midline, reflecting that the majority of the vascular components of the mediastinum are just to the left of the midline. For example, approximately two-thirds of the bulk of the heart is to the left of the midline, and the descending aorta superiorly is found to the left of the vertebral column.23 Other considerations should inform the objective, such as any required symmetry of the superior width to enable identical front and rear coverage. The values provided are based on the premise of a projectile being directed from the front of an individual, and tolerances in terms of shots angled from other directions will be incorporated based on percentiles of torso width based on the representative population.
Future considerations
The definitions of medical coverage for personal armour are not fixed. They must be chosen based on the current as well as future medical treatment options and evacuation timelines. For example, the current anatomical structures requiring essential medical coverage were based on the premise that, if injured, death is highly likely within the first 60 min unless DCS is performed within this timeframe to arrest haemorrhage.2 These medical and logistic timelines were representative of the mature medical evacuation chain present in the latter part of the UK combat operations in Afghanistan.7 24 Such timelines may not be possible to replicate in both present or future operations.7 For this reason, we recommend that future consensus will be required about the effect extended timelines may have on the medical coverage required by personal armour. In addition, recent evidence has shown that between 2004 and 2014 during Iraq and Afghanistan, of the 448 UK Armed Forces personnel killed in action before medical treatment, 57% died immediately and 68% had died within 10 min.25 Improving survival in this cohort can only be achieved by primary or secondary prevention of tissue injury, with personal armour being a significant element.
Conclusions
The acquisition of future military body armour acquisition has been assisted by defining those anatomical structures requiring coverage in the thorax and abdomen as essential or desirable. However, such medically based definitions of coverage can be challenging to implement without their translation to accepted nomenclature as used in SRDs. We have used the recognised SRD terminology of threshold and objective measurements to describe surface landmarks that represent the boundaries of essential coverage. These threshold and objective measures are underpinned by medical research of previous injury analyses and the ability to control torso haemorrhage from injury both now and in the foreseeable future. This will optimise future body armour design by enabling trade-offs between anatomical coverage and other requirements such as mobility or equipment integration.
Ethics statements
Patient consent for publication
References
Footnotes
Twitter @davidnnaumann, @maxmarsden83
Contributors All authors were equally involved in the design and preparation of this manuscript. JB takes overall responsibility for it.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.