J R Army Med Corps 2003; 149: 5-14
FOCUS ON ...
Penetrating Brain Injury In Military Conflict: Does It Merit
Introduction environment. The established experimental
One of the primary goals of the military models of TBI understandably focus on
scientist addressing the prevention of severe blunt head injury; this is much more
trauma, is to develop new concepts for frequent than PBI in a civilian setting.
attenuating energy transfer to the body from Furthermore, PBI in a civilian environment
either penetrating, non-penetrating or blast is different both in the characteristics of
impacts. Personal armours have deficiencies, injury and outcome to that seen on the
both in the body coverage achievable battlefield when helmets are frequently
without degrading military performance, worn. Militarily relevant PBI is an under-
and in the inherent ability of the materials to investigated field and receives little attention
attenuate high energy impacts, particularly in research laboratories. Indeed, previous
from high energy bullets and anti-personnel models of PBI involving the use of
fragments. Protection of the head from these projectiles fired into the brain have
types of projectiles is a difficult task – succumbed to political pressure following
personal armour materials are available to animal rights activism (1).
stop very high energy projectiles (even up to The aims of this article are to:
12.7 mm bullets), but the weight of these • examine the nature and extent of the
technologies precludes them from use on problem of PBI in the military
helmets. It is inevitable, therefore, that environment;
practical military helmets cannot stop high • identify the key clinical issues wherein the
energy penetrating projectile impacts; they military scientist may profitably focus
are remarkably effective however, against the research to result in more effective
principal threat in war – low energy anti- treatment of the brain-injured casualty,
personnel fragments. The development of particularly in the early stages of the
practical helmets capable of stopping high injury;
energy bullets is constrained by the • provide a clinical basis for new approaches
limitations of currently available materials. to the protection of the head from high
Penetrating wounds to the brain continue to energy penetrating projectiles; specifically,
be a feature of military conflict. recognising the current inability to stop
There are two types of traumatic brain high energy projectiles and the merit in
injury (TBI), blunt and penetrating. The transforming a high energy transfer
mechanisms are very different. Blunt injury penetrating wound to the brain into a low
involves the coupling of linear and rotational energy transfer wound using lightweight
acceleration and deceleration forces into the materials.
brain tissue. The resultant impacts of brain
tissue within the skull, and the tortional Ballistic Considerations
forces in particular, lead to primary brain Penetrating brain injury generally results
injury, complicated by secondary damage as from bullets, munition fragments and low
a result of subsequent pathological velocity objects such as arrows and knives.
processes. Penetrating brain injury (PBI) Penetration is a function of the available
involves local forces and stress waves that energy of the projectile, and the retardation
radiate out from the injury track, especially afforded by the tissues. The retardation
in the case of high available energy bullet transfers energy into the tissues; the energy
and fragment injury. does work on the tissues resulting in
What is the status of research into the damage. The retardation is a function of the
Sqn Ldr W Sapsford medical management of brain trauma – shape of the object (presented area), the
MA MB BChir FRCS penetrating and non-penetrating, civil and angle of approach and the properties of the
RAF military? Experimental research to enhance tissues. Brain injury is further complicated
management (and indeed protection) by the generation of secondary bone
Honorary Research requires models – tools to develop fragments and multiple metallic fragments
Fellow principles.There are several different models from the disrupted casing of the bullet.
Defence Science and
of TBI, both penetrating and blunt; using Lower available energy projectiles, such as
Technology techniques such as fluid percussion, cortical small anti-personnel fragments, arrows and
Laboratory,Porton, contusion, single artery occlusion, forebrain knives create a track of primary tissue
Salisbury, Wiltshire, ischaemia and stab wounds, but few address damage without substantial gross injury
SP4 0JQ. the issues relevant to PBI in the military peripheral to the track. Higher available
6 Penetrating Brain Injury
energy projectiles, such as bullets, result in a through” wounds).
more complex wounding pattern. A low These ballistic factors explain the span of
available energy bullet may transfer injuries observed in tissue penetration by a
sufficient energy to create a permanent track projectile. With low energy transfer, tissue
of tissue injury as it penetrates the brain, destruction is primarily limited to the track
crushing and lacerating the tissue in its path. of the missile, whereas high energy transfer
Additionally, the bullet will also produce a rounds destroy much more tissue along and
small temporary cavity, and stress (pressure) peripheral to the injury track, especially in
waves. High available energy projectiles such relatively inelastic tissue, such as the brain.
as rifle bullets will normally transfer large In practice, high energy transfer wounds
quantities of energy and produce large to the brain are invariably fatal. However,
temporary cavities, and stress waves of great the division of missiles into high- and low-
magnitude. The transfer of energy from the energy classes is arbitrary; a broad spectrum
bullet to the tissue occurs radially from the of energy levels is delivered to the tissue by
primary track, compressing the tissue high- and low-energy fragments as well as
tangentially. The temporary cavity rapidly bullets, ricocheting bullets and the
expands, reducing pressure below penetration of helmets by missiles.
atmospheric and sucking debris into the
wound; it then collapses.The cavity will then The Nature and extent of PBI
undergo several smaller expansions and Penetrating Brain Injury can be defined as
contractions of diminishing amplitude. any injury where the dura is breached and
Within an inelastic tissue like the brain, the brain is damaged directly.This may be by the
extent of injured tissue may be 10 to 20 passage of a missile or any other penetrating
times the size of the projectile. object, or indirectly by the transfer of energy
The clinical effect of the temporary cavity or local shear caused by, for example, dural
on tissues depends upon their mechanical penetration by depressed skull fracture. PBI
properties, and the function of the tissues. In can be differentiated into the following
the case of brain, a notable feature categories:
influencing the transfer of energy and the • Penetrating - a foreign object penetrates
mechanical (and functional) injury is the skull and dura and remains lodged in the
presence of the cranial vault and base. The intracranial cavity;
formation of a large temporary cavity may • Tangential - a foreign object glances off the
devastate the integrity of the vault. The skull, frequently driving bone fragments
cranial cavity may also reflect stress waves through the dura into the brain;
leading to complex and intense pressure • Perforating - a ‘through-and-through’
fluctuations and shear in the hemispheres injury characterised by both entry and exit
and medullary centres. wounds. Bone fragments and debris are
Handguns generally fire projectiles at or commonly present within the brain in this
near sonic velocity and are regarded as low class of injury.
available energy weapons compared to rifles
that produce projectiles at supersonic The nature of civilian PBI. Civilian PBI
velocities and have high available energy. can occur as a result of accidents with
Rifle bullets are also longer and more firearms and other implements but more
pointed than handgun rounds; the instability often it is the result of intentional injury –
of the bullet consequential to entering tissue armed conflict or suicide. In this setting, PBI
such as brain leads to tumbling (yaw). The is caused predominantly by firearms. Suicide
presented area of the bullet will increase is the single most common cause of such
during the yawing cycle, resulting in greater wounds. A substantial proportion of deaths
retardation, high energy transfer, and a large occurs in the first few hours following injury.
temporary cavity. Fragmentation and
deformation of the projectile can enhance The nature of military PBI. Military PBI
further the energy imparted to the tissue. results from armed conflict, however, civilian
Fragmenting rounds create multiple injury and military armed conflict are significantly
tracks. Fragmentation potential is increased different, resulting in dissimilar mechanisms
by scoring the jacket of the bullet to promote of injury and outcome, especially death. In
deformation and break-up (Dum-Dums) or this setting, and in unprotected troops,
by filling the round with pellets (the Glaser penetrating injuries are predominantly
round). In order to reduce “superfluous caused by shell and mortar fragments. The
wounding”, military bullets are jacketed to use of rifles discharging high energy rounds
inhibit disruption of the projectile (The on the battlefield leads to such damaging
Hague Peace Conference 1899). For police cerebral injury that the majority of those
use, deformation may be enhanced by suffering high energy transfer wounds to the
hollowing the point of the bullet so that it head presumably never reach medical care.
expands on impact, creating a larger The result is that in the military
permanent wound track, increasing energy environment, the surviving PBI population
transfer and reducing the incidence of is skewed towards those with lower energy
perforation of the body (“through and fragment wounds. This skewing is further
W Sapsford 7
accentuated by such moribund severely injury at 42% but only 20% of this CNS
brain injured casualties receiving a low injury was the result of craniocerebral
priority for transport to rear echelon medical penetration, the remainder being blunt
care and the prolonged time for evacuation trauma. The overall mortality rate for PBI in
to occur in these hostile environments this civilian study was therefore about 8%.
compared to the civilian environment. Of the total of those who died of CNS
Appropriate medical resources available injury a third (35%) died before reaching the
within the first ‘golden hour’ are negligible. hospital and of the two-thirds (65%) who
Furthermore, compared to the civilian did reach the hospital and died
setting, triage and resuscitation are more subsequently, almost half (42%) had
difficult, the skill levels of first medical gunshot wounds to the head (18). About
providers is different, the likelihood of 16,500 people die of gunshot wounds to the
wound contamination in battlefield PBI is brain each year in the USA (19,20),
increased and early treatment facilities are approximately half of the total of 33,000
more rudimentary. Additionally, the ability fatal shootings. In two series of civilian
of surviving casualties to reach higher levels patients with PBI that included patients
of medical care is also compromised. found dead at the scene or on arrival at the
However, PBI in the military setting does hospital, the mortality rate was 83% - 93%
occur mainly in young men in excellent (12,21). Thus, in a civilian environment
physical condition. where handguns are commonplace (such as
in the US) PBI is very often fatal and it
Hospital mortality rates of military and accounts for 8% of all post-injury deaths.
civilian PBI. Death rates from PBI are Computed tomography scans (CT)
lower for those casualties reaching medical identifying the location of trauma in the
care in the military setting compared to the brain of those sustaining PBI have enabled
civilian setting; many military casualties will an association to be made between the site of
already have succumbed in the field. The PBI and mortality. Twenty three percent die
percentage of patients with PBI in hospital following unilobar injury, 40% where the
who subsequently die is presented in for mid-sagittal plane is breached, 53% if the
various conflicts (Table1). bullet crosses the mid-coronal plane and
75% if both these mid-planes are crossed.
Conflict Mortality - percentage of Source Transventricular injuries are also associated
PBI casualties in hospital with a high mortality as is fragmentation of
WWII 10-13 (2, 3) the bullet (7,11,22,23). The majority (80%)
Korea 10 (4) of fatal neurotrauma is, however, blunt and
accounts for 34% of all post-injury deaths.
Vietnam 30 (5)
Lebanon 26 (6, 7) Military incidence of PBI mortality. It is
Iran-Iraq 16 (8) estimated that TBI, in all its forms, is one of
The data for the Iran-Iraq war only includes casualties the leading causes of combat injury
reaching a tertiary referral centre, a mean of 49 hours
accounting for 20% - 25% of all battle
incurred wounds in the modern theatre of
Table 1. In-hospital mortality rate for penetrating brain war (the leading cause of combat injury is
injury. limb injury). Bellamy estimated that 50% of
PBI casualties will die immediately or
By comparison, the mortality rate in shortly after wounding (killed in action,
civilian PBI amongst all-comers admitted to KIA). He also estimated that 80% of those
neurosurgical centres varies between 34% with TBI, surviving to reach medical care,
and 79% (9-17). If patients in the series that have PBI (24). Of those with craniocerebral
had no dural penetration (11,14) and ‘mild’ injuries who reach medical care, 43%
injuries (GCS 14-15) (15) are excluded, the ultimately die of wounds (DOW) (25).
mortality rates are uniformly above 60% for These figures suggest that, of those
civilian PBI – less die outside medical combatants receiving a TBI, the total
facilities because they are transported mortality rate from PBI is approximately
quickly to hospital. 67%, consisting of the 50% who are KIA on
the battlefield (assuming that they all died of
Civilian incidence of PBI mortality. In PBI) and the additional 17% who DOW
her reassessment of the epidemiology of under medical supervision. The latter figure
trauma deaths in a civilian trauma centre in agrees well with the known fatality rates of
the US, Sauaia reported that the most between 10% - 30% of PBI in various
common mechanism of death following conflicts who are accounted for because they
trauma was penetrating injury at 49%. survive to reach medical care (2-8). These
Gunshot wounds accounted for 42%, stab figures also compare very favourably to
wounds represented a further 6% and other those found in the civilian environment,
objects caused 1% of penetrating injury where the total mortality rate from PBI is
(18). The most frequent cause of post-injury between 83% - 93% and a “died in hospital
death was central nervous system (CNS) rate” of 60% or more (Table 2).
8 Penetrating Brain Injury
Penetrating Brain Injury Military Civilian
Incurred on the battlefield
Overall Incidence 20% 8%
Percent of all traumatic injuries
Hospital Mortality 10 – 30% 60 – 79%
Percent of admissions Died of wounds
Low available 7.5% Low available energy 60 – 79%
energy missile missiles predominantly
High available 23 – 50%
Pre-hospital mortality 50% 7 – 17%
Killed in action
Total Mortality 67% 83 – 93%
Percent of all PBI casualties
Table 2. Estimates of the incidence and mortality of PBI in military and civilian environments.
Whilst it is true that few will survive a The incidence and mortality figures
perforating, through-and-through PBI and presented here are summarised and shown in
any injury to the head from a high available Table 2. All the figures are approximate and
energy projectile is invariably fatal, many derived from a number of studies. The table
penetrating and tangential PBI injuries with enables a comparison to be made between
skull and dural penetration, are survivable. military and civilian PBI. The high overall
Aarabi analysed outcome in 435 casualties mortality in the civilian environment prob-
suffering PBI with dural penetration from all ably results from the high incidence of
missiles (low and high-energy) in the Iran- suicide by gunshot.
Iraq war who survived to reach a If the soldier survives the initial trauma and
neurosurgery centre (8) (Table 3). reaches medical attention (a 50% chance),
he/she then has a 57% chance of survival
Type of penetrating Incidence (%) Mortality (%) following PBI from projectiles, presumably,
of lower energy. In other words, up to 30% of
Penetrating 61 19.9 victims of TBI (PBI) survive and will also
Tangential 29 15.6 subsequently lead a reasonable quality of life
Perforating 9 48.8 (27). This bears very favourable comparison
to civilian PBI, (but not to civilian TBI that is
Table 3. Penetrating brain injury type and mortality (from associated with an 80% survival rate as it is
predominantly blunt trauma), and to the
survival rates seen after cardiac arrest outside
It is assumed that helmets were available hospital, (0.3%) despite the resources and
to these combatants in the Iran-Iraq war, but training devoted to this disease.
it is not stated whether they were worn or
how effective they proved. It is estimated The Opportunities To Improve
elsewhere that between 23% and 50% of Survival Following PBI
high-energy bullet PBI is fatal in those who The majority of deaths occur on the
reach medical care. In the case of low-energy battlefield before evacuation to medical
PBI, the hospital fatality rate is estimated at treatment facilities. Bellamy estimates that
only 7.5% (5,26). for every casualty who dies of wounds in a
In combat, involving numerous soldiers medical treatment facility, up to 9 have
(large unit or high intensity fighting), up to already been killed in action. Thus, in order
80% of PBI is caused by low-energy missile to significantly improve combat casualty care
injury such as fragments. In some military and given optimal circumstances (such as
scenarios, largely involving urban operations available in Vietnam), the emphasis must be
or operations against semi-organised pseudo- placed on field medical care, or the pre-
military factions (asymmetric warfare), there hospital phase of patient management by the
may be a higher frequency of bullet wounds combat medical technician and sub-
compared to fragmentation injuries. Thus, in sequently, the staff at the regimental aid post
general, there is a high rate of PBI in the (24). The target should be to improve the
military environment (80% - 90% of all care of casualties who become listed as KIA
TBI), but it is predominantly low-energy in rather than those who are ultimately listed as
nature (80% of all PBI) and caused by DOW.
fragments and other missiles. Certain Advances in the composition and design of
operations, however, will expose the soldier combat clothing, in particular the helmet,
principally to high available energy bullets. may contribute to a reduction in PBI
For the former, a mortality rate of 7.5% mortality; they will not eliminate it. Measures
demonstrates a good chance of favourable to improve forward resuscitation include
outcome (in terms of mortality) for the ensuring that a casualty’s airway (A) and
soldier; the same cannot be said for the latter. breathing (B) are scrupulously maintained
W Sapsford 9
and the early recognition of haemorrhage reduce PBI from missiles passing beneath the
(C), either overt, and thus controllable by rim into the base of skull (however, the
compression, or incompressible truncal helmet must also allow the soldier to use
blood loss, and thus uncontrollable without headphones and other equipment such as
surgical intervention. There has been respirators). An approach taken with
renewed interest recently in the management protection of the lower limb from anti-
of haemorrhage, the most common cause of personnel mines is to recognise that for
death in both the civilian and military wearable footwear, total protection is not
environments at 50% mortality of both those achievable.The strategy is to use materials to
found dead at the scene, and those who die attenuate the energy sufficiently to reduce
subsequently (18,24). Emphasis is now the clinical impact of the trauma, both
placed on the pre-hospital management of acutely, and with regard to remaining
haemorrhage, hypotensive resuscitation function. Could such an approach be taken
protocols and different management with PBI? Should we recognise that with
strategies based on the need to get those with current materials, absolute protection is not
uncontrolled haemorrhage to surgical achievable, and the target should be to
treatment as rapidly as possible.There is also further reduce energy transfer? Transposing a
research underway in UK, US and Canada high energy wound into a low energy one by
to identify and assess novel fluids for dissipating energy in the helmet penetration
resuscitation, such as hypertonic saline process could significantly increase the
dextran (HSD) and liposomally encaps- potential for survival to reach medical care.
ulated haemoglobin-based oxygen carriers
that can be deployed in the field. Antishock Pre-Hospital Management–
drugs, such as recombinant activated factor
VII may also have a pre-hospital role in ABCs
arresting uncontrolled haemorrhage acutely, There has also been a revolution in the field
allowing time for rearward evacuation to management of battlefield casualties with the
take place before exanguination occurs. widespread adoption of the principles of Pre-
Evacuation delays, pre-treatments and the Hospital Advanced Trauma Life Support
delivery of medical treatment once in a (PHTLS) (29) and Advanced Trauma Life
hospital will also be discussed to evaluate Support (ATLS) (30) within the military. In
their potential impact on the survival of the British armed forces, these principles
casualties of PBI. have been incorporated into the Battlefield
Advanced Trauma Life Support (BATLS)
Prevention – Helmet Design course (31), directed specifically at the first
There is little work to identify where responders - the Combat Medical Tech-
improvements can be made in the pre- nicians. All these protocols are characterised
hospital management of patients with PBI, by emphasis placed on the maintenance of
50% of whom die on the battlefield. Physical the airway and breathing in the immediate
protection from PBI is plainly an important, post-injury period and this is likely to have as
but difficult issue. Current helmet huge an impact on the outcome of casualties
compositions and designs and high levels of suffering from PBI as any other single
troop discipline (which ensured soldiers change. The opportunity to improve overall
actually wore their helmets during the Gulf survival of PBI casualties therefore exists by
conflict) resulted in only one US soldier improving the first aid skills of the soldier,
requiring neurosurgery for a base of skull and management of the airway and breathing
PBI in the Gulf conflict. This compares by the first medical attendants (especially
favourably to the predicted incidence of four, tracheal intubation). It remains to be seen
from the 143 soldiers wounded by missiles whether the salvage of potentially moribund
(28). In the Vietnam war, the helmet PBI casualties by the application of these
originally designed in WWII was worn, and principles should even be attempted on the
helmet discipline was poor; 98% of PBI battlefield as many will inevitably die when
occurred to the cranial vault (28). Similarly such care must eventually be abandoned as
in a series from the Lebanese conflict, 87% futile.
of PBI was craniocerebral injury (7). The TBI is frequently associated with
Gulf experience represents a dramatic haemorrhage from other bodily regions. In
improvement, albeit the number of such the US civilian environment, 35% of patients
casualties was very small. with severe TBI are hypotensive on initial
It is possible that a helmet could be presentation and these patients demonstrate
produced from known materials that will twice the mortality and a significant increase
prevent TBI or PBI from a high available in morbidity compared to non-hypotensive
energy military rifle round. However, the patients (32). It is likely that this association
load to the head and neck from the heavy is more frequent in the military environment
materials such as ceramics that would be with the preponderance of penetrating
required to stop a high energy rifle round injuries over blunt trauma. The attention to
preclude general combat issue of such appropriate resuscitation in the field, the
technology. Alterations in design could development of better fluids for resuscitation
10 Penetrating Brain Injury
and the application of the adjuncts to the probability of being KIA by any given
resuscitation, such as recombinant activated wound was greater than in the Korean War.
factor VII, may well have a significant This was most likely to be due to the reduced
secondary impact on survival following PBI. evacuation times in the latter conflict – two
Traditionally, patients with TBI are to four hours as opposed to six to eight hours
aggressively resuscitated with large volumes in WWII. In Vietnam, the evacuation time
of crystalloid with the goal of rapid volume was reduced further to one to two hours and
expansion to restore the blood pressure to the percentage of casualties who received a
normal, baseline levels (33). However, recent severe injury and died before evacuation was
laboratory studies and a single clinical study 20%. The British further reduced evacuation
have demonstrated that aggressive fluid times in Salalah, Oman in 1972-1973 and
resusci-tation in the presence of uncontrolled the number of similarly injured Omani
haemorrhage from trauma results in an casualties who died was 10% (albeit the
increase in haemorrhage volume and greater numbers in this conflict are small). Bellamy
short-term mortality compared to a regimen predicts that the KIA rate will be 20% if
of limited, hypotensive resuscitation or no evacuation occurs within the “golden hour”,
resuscitation (34-38). As a result, some 26% if evacuation occurs within the
investigators recommend that the resus- militarily relevant “golden six hours” and
citation of trauma patients be limited (or 32% if evacuation is delayed to 24 hours
maintained at hypotensive levels) until (24). In more recent warfare, the evacuation
surgical control is achieved, thereby time has been longer than that seen in
converting the uncontrolled into controlled Vietnam. In the Gulf War in 1991, the
haemorrhage. Aggressive resuscitation can median injury to admission interval was 4.41
then be started with the aim of achieving hours during the ground offensive (45), in
physiologically normal baselines. This policy Afghanistan in 2001 – 2, this delay increased
has been adopted by the British military in to 8 hours (personal communication). In the
their Battlefield Advanced Trauma Life Falklands conflict the evacuation delay was
Support manual (31). as long as 16 hours (personal comm-
Research is underway into the use of such unication).
hypotensive resuscitation regimen in PBI requires the evacuation of casualties to
combined models of TBI and uncontrolled rearward specialist neurosurgical units to
haemorrhage to establish whether this improve the survival of these severely injured
approach is appropriate in these patients, due patients. This is reflected in epidemiological
to the risk of exacerbating the secondary statistics which show that, whilst haemorr-
brain insult by hypotensive resuscitation hage from all causes is responsible for most
(39). There are also laboratory studies early deaths following admission to a trauma
centre, TBI is a major cause of late death
underway to evaluate TBI and haemorrhage
(greater than 48 hours following admission),
with potentially protective drugs (personal
second only to multiple organ failure (18).
communication) and the potential benefits of
By comparison, there are very few deaths
HSD for resuscitation in TBI (40-44).
from haemorrhage at this stage.
Finally, research is taking place in related
areas, such as the use of HSD as the initial
fluid of resuscitation following blast and Pre-treatments
Very little experimental research into
haemorrhage (both controlled and
penetrating brain injury has been
uncontrolled). As the science of resuscitation
undertaken, despite the serious problem it
in traumatic uncontrolled haemorrhage
presents both to military personnel and
develops, so research into the impact of
civilians. Investigators have consistently
potentially beneficial resuscitation regimen
shown that PBI causes profound cardio-
on concomitant military trauma, such as
respiratory effects. Indeed the first to report
blast and penetrating brain injury, must
these effects was Horsley in 1894 (46). He
follow, just as it does in civilian TBI. noted a transient apnoea following a side-to-
In summary, the prompt institution of side cerebral injury with a pistol and
supportive care by the principles set out in attributed this to a ‘hydrodynamic effect’ on
the PHTLS, ATLS or BATLS and attention the tissue of the brain that increased the
to resuscitation of casualties with extent of the injury beyond the projectile
haemorrhage and PBI may improve the diameter. This ‘hydrodynamic effect’ is
outcome of this serious injury. comparable to the result of a bullet fired at a
tin can. If the tin is empty, small entry and
Evacuation Delays To exit holes are seen; if it is full of water, the tin
Medical Care will explode. Crockard (47,48) investigated a
The longer that the severely injured casualty similar, more controlled injury in primates.
remains on the battlefield, the greater the He produced a ‘clean’ wound, away from
probability of death and therefore of being vital structures and major blood vessels, thus
classified as “killed in action” (KIA). Bellamy avoiding obfuscating haematoma develop-
analysed the effect of evacuation times on the ment and skull fragment penetration and
KIA rates in several conflicts (24). In WWII, permitting a study of the generalised
W Sapsford 11
intracranial results of missile injury. He to thoracic blast; 4) centrally administered
noted a bradypnoea or transient apnoea after methiothepin (a central 5-HTIAIC receptor
impact, depending on the kinetic energy of antagonist) potentiated the apnoea and
the missile, a prolonged bradycardia lasting bradycardia and led to an early death.
between 10 to 30 minutes and a period of Further work demonstrated that a centrally
hypotension for a few minutes following acting and centrally administered 5-HT
injury. In the higher kinetic energy group, agonist, 5-carboxamidotryptamine (5-CT)
apnoea requiring immediate ventilatory as a pre-treatment attenuated the brady-
support and more profound bradycardia and cardia seen following primary thoracic blast
reduction in blood pressure were observed. and that the respiratory stimulant doxopram
Crockard argued that these effects were due significantly reduced the duration of apnoea.
to the ‘hydrodynamic effect’ of the missile This series of studies suggested that the
being directly relayed to the structures reflex elicited by thoracic blast and that
around the third ventricle and midbrain. elicited by pharmacological stimulation of
Subsequent workers (20,49) demonstrated pulmonary afferent C-fibres does not share a
similar results and drew similar conclusions. common central nervous pathway. The work
Carey (20) discussed the pressures induced indicated that another as yet unknown
by a missile in water and tissue. He afferent pathway is activated by primary
described: 1) an extremely high juxta-missile thoracic blast.What is not in doubt is that the
pressure, immediately in front of and at right higher centres influence the response of a
angles to the missile, responsible for tissue model to primary blast injury.
destruction along its path; 2) kinetic energy Sarphie has shown fissures in the floor of
transfer, creating the temporary cavity the fourth ventricle in rats following a
behind the missile; and 3) a longitudinal penetrating injury of the sensorimotor cortex
‘strong shock’ (stress) wave pressure. The (52). The respiratory and cardiovascular
latter is a steeply rising, extremely brief centres in the rat brain stem are just beneath
(lasting in the region of 10µsec), high- the floor of the fourth ventricle and the
pressure compression front that moves conclusion drawn was that these fissures
spherically away from the strike point of the damaged the brain stem respiratory and
missile at approximately the speed of sound cardiovascular centres causing the physio-
in brain tissue. logical triad of apnoea, bradycardia and
A shock (or more accurately stress wave) hypotension demonstrated in PBI. The rat
propagating through tissues is the same model subjected to primary blast injury to
phenomenon seen in primary blast injury. the thorax in the experiments had no head
There are two critical determinants of protection. It is conceivable that the blast
survival following primary blast: the waves could affect the cardiorespiratory
pulmonary injury and the acute cardio- brain centres in a similar manner to the stress
respiratory responses. Guy (50,51) demon- waves that occur in PBI, either directly, or via
strated a reflex triad of apnoea, bradycardia transmission of the stress waves from the
and hypotension following moderate thoracic chest to the CSF and the brain. If so, brain
primary blast injury in a rat model and stem damage from blast waves might
showed that is not evident following blast influence the physiological triad of responses
injury to the abdomen. He proposed that the that occurs following primary blast injury.
responses were reflex in nature, as they are However, since the apnoea and bradycardia
not instantaneous, and that the apnoea and following a blast injury are abolished by
bradycardia can be prevented by bilateral bilateral vagotomies, the most important
vagosympathectomy. He further postulated effects are mediated via the yet to be
that one possible pathway is the reflex elucidated afferent pathway from the chest.
elicited by pulmonary afferent C-fibres If similar brain stem damage occurs
(pulmonary J-receptors), activation of which following blast injury as has been
produces the triad of apnoea, bradycardia demonstrated in PBI, there is an opportunity
and hypotension. Currently unpublished for research into treatments to abolish the
work for the Ministry of Defence, in which apnoea, bradycardia and hypotension
various pharmacologic interventions were following PBI, just as has occurred in
used as pre-treatments to try to favourably primary blast injury research. In particular,
influence the physiological triad, showed that if the apnoea could be abolished or
blockade of the known chemical transmitters attenuated, this may lead to a significant
in the pulmonary C-fibre did not influence improvement in survival both following PBI
the physiological triad. This work and primary blast injury. It has already been
demonstrated that: 1) bilateral cervical demonstrated that the central respiratory
vagosympathectomy abo-lished the apnoea stimulant doxapram, peripherally admin-
and bradycardia and attenuated the istered within seconds of a primary blast
hypotension; 2) atropine only attenuated the injury to the chest, was able to stimulate
bradycardia; 3) peripherally administered respiration and significantly reduced the
ondansetron (a 5-HT3 antag-onist which period of apnoea. It also attenuated the
interacts with 5-HT activated pulmonary C- hypotension somewhat. Veterinary surgeons
fibre afferents) did not modify the response use a soluble form of doxapram that dissolves
12 Penetrating Brain Injury
on the tongue to stimulate respiration in Protection: The current composition and
neonatal lambs. Could this type of approach design of helmets (supported by a doctrine of
be useful in PBI? use) have already had a substantial impact on
Carey (20) argues that following PBI, the PBI from low energy projectiles and some
integrity of the medullary centres is the bullets. A wearable helmet capable of
predominant factor in determining whether stopping high available energy projectiles
an individual lives or dies, provided excessive remains elusive. However the very different
intracranial bleeding does not occur. The survival rates following penetrating brain
energy transfer of the missile may determine injury by high energy compared to a low-
whether apnoea occurs and its duration, energy missiles (50% and 7.5% respectively)
ultimately causing death where the suggest that improvements in helmet design
medullary centres are irreversibly damaged. to convert high energy projectiles to the
Some casualties who have sustained helmet into low energy wounds to the head
hemispherical brain damage and are may significantly improve survival following
rendered temporarily apnoeic may possibly PBI.
be saved by prompt respiratory support (the
aforementioned principles of first aid and the Medical management: There has already
ABC of resuscitation) and respiratory been a revolution in the field of first aid and
stimulants, either as pre-treatments or as the skills of first medical responders
post-injury therapies administered in the following the introduction of the principles
field. Such pre-treatments or acute of ATLS in the late 1970’s - a ‘gold’ standard
respiratory support would raise notable of trauma care. These principles have since
logistic, operational and doctrinal issues. been widely disseminated through courses,
Current practice should not inhibit a review such as ATLS, PHTLS and BATLS. Prompt
of the benefits of reversing the inevitable assessment and maintenance of the airway
apnoea from PBI and blast injury. and breathing in a casualty following PBI is
likely to be the most important intervention
Post Admission To Definitive in their survival.
Haemorrhage management is undergoing
Medical Care a major review. It seems likely that the
There is scope to reduce the mortality from standard ATLS guidelines - that all casualties
PBI once a casualty is delivered to definitive who are shocked following trauma, should
medical care. Definitive medical care, in this receive a bolus of two litres of crystalloid (or
context, refers to a field hospital where the 20 mL/kg) rapidly - will change to
full protocol of the ATLS can be delivered, incorporate the concepts of hypotensive
including definitive haemorrhage control, resuscitation, especially in the case of non-
CT scanning and surgical decompression compressible haemorrhage into a body
and debridement of intracranial lesions. cavity. This recognises the need for rapid
Mortality from PBI in this setting is, evacuation to surgical care where hae-
however, frequently the result of a formal morrhage can be definitively controlled. The
declaration of brain death and also from management of TBI is also following suit. A
other conditions that subsequently casualty, dying from poorly managed
complicate the management of any severely uncontrolled haemorrhage, is less likely to
injured casualty, such as sepsis and multiple survive a TBI, as hypotension contributes to
organ failure; thus these deaths do not apply secondary brain injury, and consequently
specifically to PBI. It is conceivable that significantly increases mortality.There is also
some of those dying of wounds in the PBI interest in novel fluids of resuscitation, such
category could be salvaged by improved as small volume hypertonic solutions of
surgical and/or anaesthetic management of saline (HSD) and haemoglobin-based
those casualties dying from sepsis and oxygen carriers, and pharmacological agents
multiple organ failure.These are traditionally with the potential to arrest non-compressible
areas of interest amongst intensive care haemorrhage such as recombinant activated
physicians and surgeons and a large fraction factor VII.The impact of these developments
of trauma research funding is already spent in fluid resuscitation on the management of
on these problems. Nevertheless complete blunt brain injury is being reviewed; should
salvage of these casualties would only have a this not also be extended to penetrating brain
modest impact on combat casualty care as injury?
sepsis and/or organ failure currently cause Logistical considerations determine the
only two to three percent of total combat delay in evacuation of an injured soldier to
mortality (24). medical care. Ideally the gold standard of less
than one hour should apply, as in civilian
Summary practice, but this is rarely possible. In
The foregoing suggests that there is merit in Vietnam, evacuation delays of a little as one
research into protection of the head from hour were possible and TBI casualties were
high available energy projectiles, and in some often transferred directly to a neurosurgical
aspects of the management of penetrating centre. Hammon states that this rapid
brain injury. evacuation helped save countless lives and
W Sapsford 13
preserved function, although it also increased haemorrhage management on penetrating
the number of near-terminal patients who brain injury, similar to those currently in use
died within minutes (5). to investigate the effect of controlled and
Pre-treatments have been studied in uncontrolled haemorrhage on traumatic
primary blast injury, some of which show the brain injury.
potential to reduce the potentially harmful
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