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Blunt Injury

Interactions that lead to injury may be characterized as blunt, sharp, or penetrating, although there is overlapping between these categories. Blunt trauma can result from falls and blows from objects with blunt (as opposed to sharp) surfaces as well as collisions with blunt objects or surfaces. The majority of physical injuries encountered in most medical practices will fall into this category. Blunt force interactions can produce the following.

Bruises (contusions): These result from the mechanical disruption of blood vessels. Blood escapes into the surrounding tissues leading to swelling and discoloration. Although cutaneous bruises are the most visible they can also occur within internal organs and tissues. Cutaneous bruises can be visually aged, although not precisely. Fresh bruises are reddish-purple and change color as the body "repairs" the injury and clears the hemorrhage. The only consistent pattern is a change to yellow initially at the periphery of the bruise, eventually fading to brown. This alteration first appears at 1–3 days postinjury. Bruises generally are resorbed within 3–4 weeks with bruises in more vascular areas disappearing more rapidly. In instances where histological examination of the bruise is possible, greater accuracy can sometimes be obtained but there is still considerable variability.

The shape of a bruise reflects the shape and nature of the object that struck the body or the surface that the body struck. This is important for both forensic and clinical reasons. Recognizing that the looped bruises noted on a child's back during an hospital ER visit were the result of its being "disciplined" with a cord or belt rather than by playing with the family dog per the history given by the caretaker could lead to a potentially lifesaving intervention (Figure 3-2).

FIGURE 3-2

(A) Bruises may take the shape of the object that caused them—in this case a belt buckle. (B) "Tramline" bruises showing a distinctive parallel pattern result from skin impact with elongated rounded objects that force blood to the margins of the impact. This example shows curving of the bruises produced by a flexible object; an electrical cord.

Abrasions (scrapes, "burns"): These are the consequence of interactions that are tangential to the injured surface and result in damage or loss of the superficial and often deeper layers of skin. Such injuries are common in sports and the ordinary play of children and adults. They can be particularly extensive when high-speed interactions are involved such as a fall from a moving vehicle, such as a motorcycle (Figure 3-3).

FIGURE 3-3

Thigh abrasions produced by sliding contact with pavement.

Lacerations (tears): These occur when the integrity of the skin or other tissue is disrupted due to crushing or torsional forces. They are more common over bony prominences where skin can be compressed between an impinging object or surface and underlying bone. An identical blow to the head that leads to a scalp laceration may only produce a bruise in a part of the body without underlying bone such as the abdomen. A laceration is characterized by irregular, often bruised, and abraded margins. The tissues at the margins may be devitalized to the extent that clinically debridement may be required before the edges can be reapproximated. The term laceration should only be used for injuries of this nature and not for those caused by sharp objects. Like bruises the size and shape of a laceration provide information about the nature of the object or surface that produced it (Figure 3-4).

FIGURE 3-4

(A) A linear scalp laceration produced by impact with a long blunt-edged object. (B) Stellate scalp laceration produced by a hammer blow. The skin has split radially outward from the point of contact. Note (A) is upper image.

Avulsions: These are shearing injuries caused by tangential forces. In an avulsion, the skin or tissues are substantially separated from the deeper underlying structures. A common example would be the separation of a fingernail from its bed by catching it on a protruding object. So-called "scalping" injuries where the skin of the scalp is torn and separated from the underlying skull would be another example.

Fractures: Bone may be disrupted by compression, twisting, or bending. Such fractures are described as "incomplete" when the broken parts are not separated, "complete" when they are, "comminuted" when complete and the fracture results in more than two fragments. When the overlying skin is lacerated by broken bone, it is designated as "compound." "Pathologic" fractures are those that occur at sites where bone has been weakened by natural diseases such as tumor or osteoporosis. Such fractures can be the consequence of ordinary weight bearing. There are many specific clinical designations for the fractures of various bones, often eponymic, in part, reflecting the frequency with which such injuries are consistently seen in the clinical setting; for example, Le Fort I, II, and III fractures describe trauma to the maxillae and adjacent bones, resulting from blows or other facial impacts. This reflects the earlier touched upon principle that particular injury situations often result in predictable patterns of injury.

Sharp Injury

Incised wounds (cuts): These are injuries produced by objects with sharp or cutting edges such as knives, scalpels, or broken glass. They should not be described as "lacerations!" Such injuries are characterized by distinct linear margins without bruises or abrasions. The tissues are cleanly separated down into the depths of the wound (Figure 3-6). Most "stab" wounds are caused by sharp implements and are discussed further below.

FIGURE 3-5

(A) External examination—note laceration and periorbital ecchymosis (bruising). (B) Internal examination demonstrates a partially depressed fracture of the underlying bone disrupting the middle meningeal artery. (C) Demonstrates the resultant large epidural hemorrhage.

FIGURE 3-6

Two examples of incised wounds. (Left) Incised wound of the wrist with suicidal intent. Note presence of tentative or hesitation cuts crossing the wound often characteristic of suicidal injuries. (Right) Homicidal incised wounds that demonstrate "clean" margins and characteristic gaping in the direction of tissue tension.

Chop injury: Instruments with sharp edges that are also very heavy produce injuries with both sharp and blunt force characteristics when they are used as weapons. These include axes, machetes, cleavers, brush hooks, and swords. The resulting skin wounds often have straight clean margins, since these weapons have sharp edges. When firm underlying tissue or bone is struck, it may be cleaved to an extent that would not have been possible with a lighter cutting implement. Impacted bone may show a straight-edged defect identical to the chop mark that results when an axe strikes a piece of wood. The rest of the bone underlying the impact site may also break, resulting in a complete fracture.

Penetrating Injury

Penetrating injury: These injuries can be caused by both blunt and pointed objects and those with sharp edges as well as projectiles and are characterized by the fact that they have passed through the skin and extended deeper into the body. The extent of internal trauma cannot always be appreciated by the external appearance of a wound (Case 3-2). If a wound passes completely through the body, it is described as "perforating." These terms may also be used to describe an injury to an individual organ or body structure.

CASE 3-2

A 27-year-old man got into an argument at a bar and was struck in the head with a pool cue. He was not rendered unconscious, left the premises under his own power and was seen to get into his vehicle and drive away. A few hours later his truck was noted parked on the shoulder of a nearby road. The key was turned off in the ignition and he was in the driver's seat slumped over deceased. External examination revealed a small laceration of the left supraorbital area and a periorbital ecchymosis (Figure 3-5A).

Internal examination demonstrated a partly depressed comminuted fracture of the underlying frontal bone (Figure 3-5B). The fracture line passed through the vascular groove on the inner table of the skull carrying the middle meningeal artery disrupting that vessel causing a large epidural hemorrhage (EDH). This expanding mass had led to left-sided transtentorial brain herniation and his death (Figure 3-5C).

Intracerebral hemorrhage is a common consequence of head trauma and can occur in the epidural, subdural, and/or subarachnoid compartments (EDH, subdural hemorrhage [SDH], and subarachnoid hemorrhage [SAH], respectively). EDH is almost always associated with a skull fracture that tears an imbedded or adherent arterial vessel. Because of the middle meningeal artery's course within a vascular groove in the relatively thin squamous portion of the temporal bone, it is particularly vulnerable. SDHs are usually seen over the cerebral convexities and are felt to be resulted from the tearing of veins bridging the subdural space along the falx. SAH results from disruption of meningeal or other vessels on the surface or base of the brain as may happen with the ruptue of congenital lesions, "berry" aneurysms, of the circle of Willis (see Chapter 21). SAH can also accompany cerebral contusions or from blood dissecting to the surface from deeper intracerebral bleeding.

EDH and SDH become intracranial space occupying lesions and may lead to brain stem herniation. The mechanism whereby "pure" acute SAH causes death is not entirely clear but may involve vascular spasm. In instances of EDH, SDH, and SAH, there may also be accompanying traumatic cerebral parenchymal injury that may be of greater significance than the extracerebral blood. The rapidity with which the bleeding occurs is an important factor. Slow accumulations of blood, particularly in SDHs, are often well tolerated with little or no symptoms, becoming chronic and in some instances eventually being largely organized and resorbed while a similar volume of blood accumulating more rapidly would lead to herniation and death.

Stab wounds: Such wounds are usually sharp force injuries caused by knives or knife-like objects but can also result from the thrust into or the impaling of the body onto other pointed objects, for example, screwdriver or ice pick. The depth of the wound cannot be judged by the appearance of the wound in the skin and what appears to be a small cut in the skin may in fact be a potentially lethal wound to deeper internal organs. Since a blade cuts as it passes through the skin, the defect in the skin can be longer than the width of the blade itself, and because the body and tissues are compressible, the depth of the wound may be greater than the length of the stabbing instrument. The depth may also be less since the instrument may not be fully inserted.

Gunshot wounds: These are penetrating injuries produced by rapidly traveling projectiles of small size. It is the high speed of these objects and the small area over which their resultant kinetic energy is applied that causes injury, not their mass (weight). In most firearms, the projectile whether bullet or shot is accelerated down a hollow metal tube, the gun barrel, by an expanding cloud of hot gases generated by the ignition of a quantity of gunpowder, although there are guns that use other sources of gas such as CO2 or compressed air to propel their missiles. Some of the latter can achieve velocities comparable to gunpowder weapons, though their projectiles are usually much smaller. Nonetheless they can still produce serious and even fatal trauma. The projectiles fired from guns are usually composed of lead because of its density and relatively low melting temperature that allows it to be easily cast into various shapes. The projectiles are either cylindrical, generally with a rounded or pointed nose; (bullets), or spherical (shot). The former are used in rifled weapons and the latter in smoothbore weapons (shotguns). Rifled weapons have spiral grooves cut into the bore of the gun barrel that imparts a spin to the bullet as it passes through. This, combined with the elongated shape of the projectile, gives the projectile greater ballistic stability allowing it to travel further and straighter. In a rifled weapon, only one projectile at a time travels down the barrel, although they may be capable of firing many times in rapid succession. Long-barreled rifled weapons are called rifles and short barreled ones handguns. The internal diameter of the gun barrel is its caliber that may be given in inches or millimeters. This determines the diameter of the bullet. Shotguns are smooth bored, have no internal rifling, and are designed to fire multiple projectiles, or "load," at once. This load of shot spreads out after leaving the barrel to produce a cloud of projectiles, the better to strike a small moving target, such as a flying bird. Small shot for hunting birds is called "birdshot" and larger shot or pellets for bigger game is called "buckshot." The diameter or bore of a shotgun is described in terms of its "gauge" (which is, for larger bore guns, the number of lead balls the diameter of the barrel that it takes to make up a pound). Both bullets and shot vary in size, but bullets also show considerable variation in shape while shot is always spherical. Bullets may be composed solely of lead or may be coated with another metal, "jacketed." These variations in shape and covering, in addition to variation in size (caliber), are intended to enhance the performance of the gun and/or the bullet. Lead shot may also be thinly coated with another metal and some shot are made of steel to curb lead poisoning in birds who ingest the spent shot while feeding. Large single projectile rounds, usually referred to as slugs, may be used in shotguns for larger game. Early guns, both long barreled and short, were smooth bored and usually fired single lead balls.

A bullet striking the body may not only penetrate it but may also pass completely through the body. Gunshot wounds are the most common form of perforating injuries. For medicolegal purposes, it is critical to distinguish wound entrances from exits, and it is ordinarily possible to do so in the case of gunshot wounds and often stabs and other perforating trauma.

Entry bullet wounds: When a bullet impacts a surface perpendicularly in a nose first configuration, it produces a defect that is rounded and regular in appearance. On the skin, there is often a thin collar of abrasion at the margins of the defect. Lead or other residue on the bullet may also be deposited at this margin and appear as an encircling fine gray residue or "wipe-off." If the impact is at an acute angle, the defect may be elongated or elliptical in shape. The configuration of the nose of the bullet will to some degree affect the appearance of the defect as well as the presence of intervening clothing. Typically the actual defect is slightly smaller than the diameter of the projectile. Individual shotgun pellet entry wounds will have the same appearance as bullet entry wounds (Figure 3-7 left).

FIGURE 3-7

Bullet entry and exit wounds. (Left) Gunshot entrance—note regular round configuration and marginal abrasion. (Right) Gunshot exit showing lack of marginal abrasion and an irregular configuration.

Exit bullet wounds: When a projectile exits the body, it tends to produce an irregular wound as the skin is stretched outward from within. Since the projectile is not impacting the epidermis, there is no abrasion collar. The projectile may have expanded or become distorted during its passage through the body or in the case of a bullet may now be traveling sideways or base forward so that the defect it produces is usually larger than the diameter of the projectile. It is generally the case, (with important exceptions), that an exit wound is larger than the corresponding entrance wound (Figure 3-7 right).

The core of disruption that a projectile produces along its course is related to the size of the projectile and its velocity, that is, its kinetic energy. As bullets become larger and/or move faster, they tend to produce more damage to the organs and tissues that they pass through. As a bullet becomes heavier, it also becomes larger and thus has a greater cross section leading to a larger path of injury. Some bullets are designed to expand as they pass through tissue also increasing their cross-sectional area. Similarly longer bullets tend to tumble or "yaw" as they pass through tissue and the greater exposed surface produces a larger and potentially more destructive wound track. If a bullet fragments and disperses into the tissues, it may produce more damage than a bullet that remains intact and bone struck by projectiles can also fragment and be driven into tissues along the wound track.

The velocity of projectiles varies from around 700–1500 feet/second for handguns up to 3000+ feet/second for high-velocity rifles. The lower velocity weapons tend to produce wound tracks that are approximately the diameter of the bullet, while high-velocity bullets, because of their higher kinetic energy, produce larger wound tracks than low-velocity bullets of the same diameter or caliber.

Range of fire: The distance between the muzzle of the gun and the object struck by the projectile is also an issue in gunshot wounds. It is particularly critical in determining whether a wound could have been self-inflicted and may be of importance in subsequent legal proceedings on other occasions. Range of fire may be characterized as contact, close or distant (Case 3-3).

Contact: The muzzle of the gun is against the body at the time it is discharged which is the typical situation in a suicidal wound. The expanding hot gases from the ignited powder follow the bullet into the tissues and can be visualized within the wound itself as gray sooty residues and intact or partly burned powder particles. There may be visible burning or "searing" of the margins of the entrance. In the case of large caliber weapons, the propellant gases may tear or disrupt the skin at the margins of the entrance, leading to a large irregular often stellate wound. This is most common in wounds of the head where underlying bone inhibits the dispersal of the propellant cases. With high-velocity rifles and shotguns, the head may be massively disrupted with complete or partial exenteration of its contents. If the contact is not tight, gases may escape at the margins leading to wider soot deposition and searing, burning, around the entrance.

Close: Wounds where the weapon is not in contact but close enough that powder residues can be seen on the skin or clothing. This takes the form of soot, the fine particulate smoke produced by the largely complete combustion of the powder and "stippling" or "tattooing", minute lacerations of the skin produced by the impact of unburnt or partly burnt powder particles. As the distance from muzzle to skin increases less of the lighter fine soot reaches the skin and the larger powder particles spread out producing a wider pattern of stippling. Beyond several feet, very little of these powder residues reach the skin.

Distant: No visible residues reach the skin. In the case of most weapon discharges greater than a few feet away, these residues do not reach the skin in sufficient quantity to be visualized with the eye. In the case of shotguns, which discharge multiple projectiles simultaneously, the spread of the pellets can be used to approximate the muzzle to victim distance up to many yards away (Figure 3-8).

FIGURE 3-8

A close range chest wound showing a pattern of stippling accompanied by deposition of gray soot immediately adjacent to the entry wound.

Pressure Injury

Injury resulting from pressure phenomena takes several forms.

Blast: An explosion generates a pressure wave that moves at the speed of sound. As it passes through media of different density, the speed of the wave changes. This can lead to the disruption of internal organs at air–tissue interfaces as the wave moves through the body. This internal trauma can occur in the absence of visible external injury. A blast may also cause massive direct disruption to the body, depending on its intensity and the proximity of the victim. The explosion may fragment objects in the environment and/or the explosive device itself may fragment, which many bombs, grenades, mines, and other antipersonnel devices are designed to do. These objects and fragments may then produce penetrating projectile injuries in addition to any pressure wave effects. If the explosion generates heat, thermal injury may also occur.

Elevated atmospheric pressure: In circumstances where individuals are exposed to increased barometric/atmospheric pressures, injury may occur upon their return to normal atmospheric pressure. On a too rapid return to lower pressure, gases that have dissolved in the blood (primarily nitrogen from air) come out of solution and form minute bubbles within the blood and tissues where they cause mechanical disruption and interfere with the microcirculation. If severe enough, the bubbles may produce strokes or myocardial ischemic events. First described in workers laboring in underwater pressurized chambers, "caissons," during the construction of tunnels and bridges, it is known as caisson's disease or the "bends." Today, it is mainly a hazard for divers both recreational and professional. Treatment involves placing the affected individual back into an environment of higher pressure, usually in a hyperbaric chamber, to redissolve the offending gases and then slowly decompress them.

Decreased atmospheric pressure: As one ascends from sea level, atmospheric pressure decreases and with it the partial pressure of oxygen. At elevations over 3000 m, the risk of a variety of altitude-related illnesses increases especially for individuals coming from lower altitudes who have not allowed themselves to become acclimated. The most feared consequence is the development of pulmonary and cerebral edema. This constitutes a medical emergency with return to lower altitude necessary if the individual affected is to survive. Other altitude-related conditions include systemic edema, retinal hemorrhages, general deterioration in physical and mental performance, flatus and acute mountain sickness. The latter is characterized by headache, insomnia, dizziness, fatigue, nausea and/or vomiting, loss of appetite, increased heart rate, and shortness of breath on exertion. There is considerable variability among individuals in their susceptibility to these illnesses.

CASE 3-3

A young male calls 911 and states that he was shot during an attempted robbery. He has a wound in his thigh (Figure 3-9). The authorities are suspicious of his story as he states that the assailant was standing several yards away, facing him when the shot was fired. However, the wound track is upward (see arrow upper view) and there is powder residue and soot around the entry wound (see arrow in detail of entry wound). Both wound direction and range of fire are inconsistent with the victims claim and it was concluded that the wound was self-inflicted.

FIGURE 3-9

Upper photo demonstrates upward course of wound track (arrow). Lower photo is the detailed view of entry wound surrounded by abundant sooty powder residue and soot (arrow).

Asphyxia

Asphyxia literally means without pulse but is generally defined as the deprivation of oxygen to tissues or the body as a whole. This can occur as a result of the failure of the respiratory system to take oxygen into the body, the failure of oxygenated blood to reach tissues or at the biochemical level the inability to utilize the oxygen being delivered by the circulation. During the process of death, all tissues ultimately experience asphyxia as respiration and circulation fails.

Oxygen is essential for cellular function but different organs and tissues vary in their tolerance to periods of relative or complete oxygen deprivation, hypoxia, or anoxia. The brain is the organ most dependent on oxidative metabolism and periods of anoxia that would not result in significant injury to other organs and tissues can lead to irreversible CNS damage. Obstruction of blood flow through the common carotid arteries will lead to loss of consciousness after 6 seconds. Irreversible brain injury will generally result if cerebral blood flow is interrupted for more than 3–4 minutes. Stagnant cerebral hypoxia is not as well tolerated as hypoxia with active circulation, thus the changes in CPR practice emphasizing chest compressions over respiratory, mouth-to-mouth, support. External forces and factors can cause asphyxia in a variety of ways.

Compromise of breathing: This may result from the complete obstruction of the nose and mouth, obstruction of the larynx or trachea, or compression of the chest. Placing a plastic bag over the head, a child choking on a piece of hotdog, and a man whose auto slips off a jack while he is working underneath it are respective examples of these mechanisms. Individuals with some degree of mobility impairment are at a particular risk of such injury. Small infants are susceptible because should they work their way into a position where their breathing is compromised, they are unable to extricate themselves. This is often the case in infant deaths related to unsafe sleeping environments. An infant placed in an adult bed may roll off and become wedged between the mattress and a nearby wall or headboard. Before infant crib standards were established in 1973, there was wide variation in crib sizes, the spaces between the slats on the sides, and the sizes of crib mattresses. These variations created situations where the slats were spaced widely enough for the bodies of small infants to slip between and hang themselves when the larger head would not pass through. Mattresses that did not fit tightly enough created spaces where they met the headboard and sides large enough for infants to slip into. Projecting posts or decorations could catch on articles of clothing and suspend the infant. With the adoption of crib standards and the regular review of fatal incidents involving cribs, playyards, portacribs and other such devices with recall of those found hazardous there has been a significant decrease in such tragic incidents though they are still now seen with old or defective cribs or as noted improvised sleeping arrangements.

Adults impaired by drugs or alcohol are also at risk whether by passing out in a position where their face is covered by an impermeable surface or becoming wedged between furniture or other objects in their environment with resulting chest compression. Elderly demented or otherwise impaired adults, particularly, if restrained, have similar risks. Such restrained individuals may, in an attempt to escape, become wedged under bed rails or twist their restraints to the extent that they suffer chest compression. If the restraints get around the neck, they may, in effect, hang themselves.

Compromise of circulation: Any pressure or restriction to a body part sufficient to interrupt or significantly restrict blood flow distally can lead to ischemic injury, asphyxia, to the parts affected. A simple example is the arm that "falls asleep" when left draped over a chair or bent under us while we sleep. In spite of the unpleasant temporary sensations of woodenness and "pins and needles," this almost never has any long-term consequence. In fact, short-term interruption of the blood supply to an extremity may be employed in surgery to ensure a bloodless field. When pressure is applied to the neck, however, cerebral blood flow can be compromised with potentially rapidly fatal consequences. This is the usual mechanism of death in suicidal hangings. The constricting noose or ligature initially restricts cerebral blood outflow through the internal jugular veins and then arterial flow into the brain through the common carotids. It is almost never the case that there is a bony neck injury. Neck injury is ordinarily only seen if there is a long drop before suspension occurs. Fracture of the cervical spine with high cord damage is the intended mechanism of death in "modern" judicial executions by hanging. Cerebral anoxia also occurs in assaults involving strangulation whether manual, or by ligature. Damage to rigid internal neck structures like the hyoid bones and thyroid cartilages is rare in suicidal hangings but common in assaults. Also frequently noted in such assaults are facial and conjunctival petechiae. The latter may become confluent.

Entanglement in ropes or cords is an important cause of unintentional injury in children. Dangling cords for draperies and blinds are a particular hazard to infants and small children. Many infants have been asphyxiated when cords or strings attached to toys dangled into their cribs became twisted around their necks. Cords holding pacifiers and drawstrings in clothing are similarly dangerous. In such cases, visible injury to the body is usually confined to marks caused by the offending string or cord.

Compromise of cellular respiration: A variety of chemicals and toxins interfere with cellular utilization of oxygen. These include cyanide and carbon monoxide that are discussed in another section of this chapter.

Drowning: A number of mechanisms have been proposed as causative factors in drowning; however, the simple fact remains that we cannot breathe underwater. Although there are other physiological events that may occur during a drowning episode, ultimately death results from asphyxia. Survivors of drowning episodes may develop pulmonary complications from aspirating contaminated water in addition to any hypoxic cerebral injury. Many who are initially successfully resuscitated eventually succumb to adult respiratory distress syndrome (ARDS, see Chapter 8), although usually also having sustained significant cerebral damage from hypoxia. Victims of immersion in cold water, particularly children, may be more salvageable than when the event occurs in warm water because of the protective effects of the rapidly induced hypothermia on the central nervous system (or brain).

Oxygen-deficient environments: Some asphyxiations result from a lack of oxygen in the local environment. This may occur if the air is displaced by other gases or fumes even if those gases or fumes are not themselves toxic. Under some conditions oxygen may be depleted in a confined location by biological or chemical processes and of course it is deficient at high altitude. Most of these conditions involve occupational, industrial, or agricultural settings. Tanks utilized to store volatile chemicals may still be filled with fumes after being emptied and unless thoroughly ventilated may be deadly for any workers entering them without an independent source of air. Oxygen-deficient atmospheres can be found in wells and other underground spaces such as sewers. In agricultural settings, silos, grain bins, and manure pits also pose similar risks as well as the possible presence of toxic gases. Individuals may create oxygen-deficient atmospheres during the course of inhalant abuse and inadvertently asphyxiate themselves or do so deliberately as a suicide mechanism. In recent years, helium has become a popular agent for the latter.

Asphyxias may occur when externally supplied air for breathing does not contain sufficient oxygen. There are strict regulations and standards regarding the storage of compressed gases destined for industrial, medical, or other uses in part to ensure that such gases are only used for their intended purposes. In spite of these engineering controls, people still manage to connect incorrect cylinders to gas lines. There have been multiple instances involving hospitals and other care facilities when oxygen lines to patient care units were erroneously connected to other gases with tragic result.

Pathological Findings in Asphyxia

There are no specific pathological findings in asphyxias. Pulmonary congestion and edema are commonly present often accompanied by some degree of intra-alveolar hemorrhage but these are nonspecific changes. The means by which the asphyxiation was effected may result in recognizable injuries such as ligature marks in hangings and ligature strangulations (Figure 3-10).

FIGURE 3-10

Ligature marks in a suicidal hanging. The mark reflects the pattern of the rope used (shown below).

Internal neck trauma is common in assaultive strangulations. Moreover, during the assault other physical injuries may be incurred by the victim (Figure 3-11). In mechanical or positional asphyxias pressure marks, bruises and abrasions may be found marking points of contact between the victim and the compressing surfaces. In instances of neck constriction or chest compression fine capillary hemorrhages, petechiae, of the eyes and skin above the constriction/compression may occur. In many instances, however, the identification of asphyxia as the cause of death or injury comes from history and witness accounts. As earlier noted the brain is much more susceptible to anoxic/hypoxic injury than other organs and tissues. This leads to situations where an individual is removed from an asphyxiating environment, e.g. drowning, hanging, in time to preserve all organ functions other then that of the brain. Depending on the severity of the anoxic period varying patterns of cerebral injury may be seen (see Chapter 21).

FIGURE 3-11

Manual strangulation. (Left) Abrasions and bruises are visible on external examination. (Right) Internal examination demonstrates hemorrhages (arrows). There was also a fracture of the hyoid bone.

Complexity of Injuries

Many injury situations produce a complex of different types of injuries. As mentioned, an explosion can produce blunt force, penetrating, and thermal injuries. Similarly, the occupant of a motor vehicle that wrecks could incur blunt force injuries, cuts from broken glass or sharp metal, and thermal trauma should a fire break out. Occupants trapped in collapsed passenger compartments may be mechanically asphyxiated or drowned should the vehicle end up in a body of water.

Occupational Injuries

While occupational injuries will be further addressed in the chemical injury section, in the United States, the majority of acute occupational injuries and certainly the fatal ones are the consequences of physical trauma. In 2010, 87% of such fatalities were due to physical trauma with transportation-related incidents being the most common (Figure 3-12).

FIGURE 3-12

Manner in which fatal work injuries occurred (2010 data). Data for 2010 are preliminary. Note: Percentages may not add to totals because of rounding. Transportation counts are expected to rise when updated 2010 data are released in Spring 2012 because key source documentation on specific transportation-related incidents has not yet been received. Source: U.S. Bureau of Labor Statistics, U.S. Department of Labor, 2011.

Fatal workplace injuries occur mostly in men, who while accounting for 56% of the total hours worked constitute 92% of the fatalities. As would be expected certain industries and occupations are inherently more dangerous and have higher rates or injury both fatal and nonfatal (Figure 3-13).

FIGURE 3-13

Number and rate of fatal occupational injuries by industry sector (2010 data). Source: U.S. Bureau of Labor Statistics.

Construction had the highest number of fatalities, while agriculture, forestry, fishing, and hunting had the highest rates. Workers employed in fishing and logging followed by aircraft pilots and engineers respectively topped the occupations with high fatality rates (Figure 3-14).

FIGURE 3-14

Occupations with high fatal work injury rates (2010 data). Source: U.S. Bureau of Labor Statistics.

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