Asphyxia is derived from the Greek word ‘asphuxía’ meaning without pulse. However, in forensic medicine, asphyxia describes a situation where there is a lack of oxygen in the body. The commonest form of asphyxia involves physical obstruction between the external orifices and the alveoli. Other forms of asphyxia involve hindrance to exchange of oxygen between the alveolar air and blood as well as interference with utilization of oxygen in target tissue.
Asphyxia is not frequently used in clinical medicine, perhaps appropriately, given the lack of understanding of the pathophysiology in many such deaths. In legal context as well, the variance of mechanisms causing lack of oxygen in the body makes the diagnosis of asphyxia insignificant. The underlying mechanism that caused the asphyxia is more important in investigating the cause of death, as is the manner of death.
EXAMPLES OF ASPHYXIAL DEATH
Underlying Mechanism Of Death, Examples
- Lack of oxygen in the inspired air – Suffocation
- Blockage of the external orifices – Suffocation/ smothering
- Blockage of the internal airways by obstruction – Gagging/ choking
- Blockage of the internal airways by external pressure – Strangulation/ hanging
- Restriction of chest movement – Traumatic asphyxia
- Failure of oxygen transportation poisoning – Carbon monoxide
- Failure of oxygen utilization – Cyanide poisoning
CLASSIFICATION OF ASPHYXIA
Smothering – Physical obstruction of mouth/ nose – preventing effective breathing
Gagging– Physical obstruction in the upper respiratory tract
Choking – Physical obstruction in the lower respiratory tract
Strangulation – Pressure applied to neck, by means of ligature or hands
Hanging – Pressure applied to neck by ligature, constricting force being weight of own body
Compression – Obstruction to respiration due to pressure applied to chest and/or abdomen
Suffocation – Reduction of oxygen in the respired air
Carbon monoxide poisoning – Obstruction to transportation of oxygen by hemoglobin
Cyanide poisoning – Obstruction to utilization of oxygen in the cell
Drowning – A form of violent asphyxial death, wherein the entry of air into the lungs is prevented by water or other fluids due to the submersion of mouth and nostril.
Phases and signs of ‘asphyxia’
The general sequence of events in asphyxial insult consists of five stages – dyspneic phase, convulsive phase, pre-terminal phase, gasping phase and lastly terminal phase.
- Dyspneic phase
Expiratory dyspnea with raised respiration, cyanosis and tachycardia (may last for a minute or more)
- Convulsive phase
Loss of consciousness, reduced respiration, facial congestion, bradycardia, hypertension, fits (may last for a couple of minutes)
- Pre-terminal phase
No respiration, failure of respiratory and circulatory centers, tachycardia, hypertension (may last a couple of minutes)
- Gasping phase
Respiratory reflexes – loss of movement, pupillary dilatation.
- Terminal phase
Loss of circulatory and brainstem function
Traditionally, the ‘classic signs of asphyxia’ include
- Petechial hemorrhages over the face, conjunctiva, mucosa, pleura, pericardium etc.
- Congestion and edema over the face, conjunctiva, viscera
- Cyanosis over the face, lips, fingertips
These ‘classic signs’, are caused by raised intravascular pressure in blood vessels in the head and neck. However, they are not specific for asphyxia, and can be seen in a wide variety of deaths. Petechiae in face and neck require an explanation, and any evidence capable of supporting a diagnosis of ‘pressure applied to neck or chest’ should be explored.
TYPE OF MECHANICAL ASPHYXIA
Pressure to the neck
Three forms of pressure over the neck are predominant, namely manual strangulation, ligature strangulation and hanging. The sequence of events leading to death is extremely variable and can lead to variations in the development of ‘classic signs of asphyxia’. Some cases may lead to death over a sustained period of time and may show prominent signs of asphyxia, while in other cases of sustained pressure, they may be absent. Extremely short periods of pressure over neck have also demonstrated asphyxial signs.
The exact mechanism leading to asphyxia may vary and include at least one of the following:
- Obstruction of jugular veins, causing impaired venous return to the heart – resulting in cyanosis, congestion and petechiae
- Obstruction of carotid arteries causing cerebral hypoxia
- Stimulation of carotid sinus resulting in cardiac arrest (vasovagal stimulation)
- Elevation of larynx and tongue, obstructing the airway at the level of the pharynx. Trachea and tracheal cartilages are resistant to compression.
Numerous recorded deaths have been studied and support assertions of rapid loss of consciousness, within 10 seconds. The time for a fatal outcome, however, is extremely variable, although analysis suggests lack of recognizable respiratory movements after 2 minutes and lack of muscle movements after 7.5 minutes. Experimental occlusion of trachea in animals have shown survival for up to 14 minutes following obstruction.
‘Vagal inhibition’ or reflex cardiac arrest
Pressure over baroreceptors present on the carotid body, at the carotid bifurcation, has been known to cause cardiac inhibition. This property has long been used in therapeutic cardiac sinus massage in patients with arrhythmia. These alterations, however, are unpredictable and fatalities have been described, with individuals collapsing after apparently minimal pressure being applied to the neck. This chain of events has been attributed to vagal inhibition due to carotid sinus stimulation. This is also called the cardiac reflex. Afferent fibers run via the carotid sinus nerve, branch of glossopharyngeal nerve, to nucleus of tractus solitarus and vagal nuclei, in the medulla. Parasympathetic nerves then innervate the heart via the vagus nerve. The lack of general signs of asphyxia is thought to imply death due to vasovagal stimulation, where the individual died before the signs could develop.
Strangulation is used to describe death caused by application of pressure around the neck, where the pressure is caused by anything other than the weight of the person’s body. Strangulation is consistently homicidal, even though accidental strangulations have been known to occur from time to time. Suicidal strangulation, however, is extremely rare and should be treated with suspicion.
Manual strangulation describes the application of pressure to the neck using hands. This is a relatively common method of homicide. This is extremely common in infants and elderly. Manual strangulation cannot be suicidal, as the loss of consciousness would cause release of pressure.
The external examination reveals bruises and abrasions on the neck. While many books describe the classic crescentic abrasions caused by fingernails, the dynamic nature of the assault often causes obscure bruises and abrasions. Similarly, typical – six pence – round or ovoid contusion, 1-2 cm in diameter may be seen at places of digital pressure. In addition to other features, it is important to remember that either the assailant or the victim may have caused these injuries.
The classical signs of asphyxia are frequently seen in abundance in strangulation, both manual and ligature. This is often because typically, more force than is required is applied when attempting to kill another person.
Ligature strangulation describes death due to pressure over the neck, causing a constricting force, using any material including cloth, rope, wires etc. Ligature strangulations are usually homicidal or accidental, while suicidal ligature strangulations are a comparatively rarer entity. As with manual strangulation, signs of asphyxia are usually pronounced and frequently, there is a clear difference in the congestion above the level of the ligature.
Frequently, a faint ligature mark is present over the neck and rarely may replicate the pattern of the ligature material. Careful documentation of ligature mark, with scaled photographs, may allow comparison with the suspected ligature material. Soft and broad ligatures may leave no evidence of compression on the skin of the neck, or even underlying structures.
Ligature mark is commonly seen as an oblique continuous mark, completely encircling the neck, although clothing, or hair, may cause break in the continuity of the mark. Ligature may show crossing of the ligature or even knots in the ligature. There may be marks suggestive of crossover of the ligature, or knots, but nothing indicating a suspension point. Ligature marks frequently harden due to drying of the abraded skin, causing a brown parchmentization.
Pressure can be applied over the neck by other means other than hands or ligature – for example, arm-lock or choke-hold. The damage to the tissue depends on the nature of force applied to the neck.
Dissection of neck structures should always be carried out in a bloodless field to minimize the occurrence of post-mortem artefacts. This can be done by first eviscerating the thoracic, abdominal and cranial contents, leading to drainage of vasculature of the neck from superiorly as well as inferiorly.
Dissection may reveal contusion over the strap muscles, sternocleidomastoid muscle as well as platysma. The superior horns of thyroid cartilage are particularly vulnerable to compressive injury, and may be fractured. The greater horns of hyoid may also be fractured, although seen less frequently than thyroid fractures. Calcification and ossification of hyoid bone and thyroid cartilage makes them more prone to injury, and are so more frequently associated with neck compression in the elderly. Neck injuries are commonly less extensive in ligature strangulation, with hemorrhage more localized, underlying the ligature.
Hanging is defined as ‘death due to suspension of the body by a ligature around the neck, with the consricting force being the complete or partial weight of body of the individual.’
Hanging therefore confines to suspension of the body by the neck. Any material that is capable of forming a ligature can be used for hanging. It is not necessary for the body to be completely suspended. The lowest height of point of suspension describe in literature, in a case of hanging, is 15-20 cm from the ground, with the body completely supine and the posterior neck just above the ground level.
A ligature mark is almost invariably present, often deep and furrowed, with discontinuations common. Discontinuity could reflect the point of suspension, or could be due to juxtaposition of hair or clothing between the ligature and skin.
The ligature rises from the point directly opposite to the point of suspension. The ligature mark forms a V-shape with the tip away from the point of suspension as well as an inverted V where the noose suspended the body.
The precise mechanism of death in a case of hanging cannot be conclusively determined, although, it is universally accepted to be a combination of mechanisms described when discussing pressure over the neck. The various combinations of these mechanisms lead to a wide variety of features being demonstrated at autopsy. As such, Death may occur faster than the time required for signs to appear, and may result in absence of signs of asphyxia, even in hangings, with complete suspension.
Hanging by judicial execution demonstrated fracture-dislocation of the odontoid process and impaction into the medulla. This usually involves a drop to a height that has been calculated to cause fracture-dislocation of the cervical spine without decapitation. This is not present in our context. However, such findings may be seen in drops from a considerable height and may result in complete decapitation. Excluding in autopsies following judicial execution hangings, neck structures in hanging are frequently inconspicuous, with no significant injuries.
Hanging is mostly suicidal, although some cases are accidental, following entanglement with wires and ropes. Homicidal ligature strangulation may be staged to resemble a suicidal hanging, and autopsy would demonstrate extensive injuries to the neck structures in such situations.
Post-mortem toxicological analysis should be performed in all suspicious cases of alleged hanging in order to determine whether the individual was capable of self-suspension.
Choking is defined as ‘obstruction of the lower respiratory tract by extraneous material’. This commonly occurs following accidental inhalation of foreign objects like food. Choking is also common following misplaced dentures in adults and inhaled objects such as small toys, balls, etc., in children.
Extracted teeth or blood from dental or ear, nose and throat (ENT) operations may occlude the airway and is an added precaution to be ensured, especially in a sedated patient. Death is commonly due to respiratory distress, with autopsy demonstrating congestion and cyanosis of the head and face.
One of the commonest causes of choking is the entry of food into the air passages. If food enters the larynx during swallowing, unless the obstruction is released, it usually causes gross choking symptoms of coughing, distress and cyanosis. However, if the piece of food is large enough to occlude the larynx completely, it will prevent not only breathing but also speech and coughing.
This is usually seen where an apparently healthy individual having a meal suddenly collapses and dies. The cause of death in such cases was thought to be heart attack, and hence the name Café Coronary Syndrome.
Pressure on the trunk can cause hindrance to effective respiratory movements and result in an inability to breathe effectively, causing death. Workers buried in earth are unable to expand their chests, leading to respiratory distress. Similarly, individuals trapped under heavy machinery are unable to breathe effectively. Individuals may be crushed by the weight of other people during stampede.
While the predominant causes of death in such situations are due to crush injuries, it is also possible for an individual to be uninjured but dies due to inability to execute respiratory movements due to the weight of the bodies on top. These examples of ‘compression asphyxia’ are called traumatic or crush asphyxia.
Another form of compression asphyxia is seen in the intoxicated individuals or individuals with impaired cognition, where the body is jammed in a position, rendering breathing ineffective. For example, the torso may be stuck in small gaps while trying to squeeze through, causing difficulty in expansion of the chest. Similarly, intoxicated individuals may die due to compression of the neck or even the chest, against the edge of the bed, resulting in restriction to breathing. While this would normally not occur in an alert individual, one who is sedated or has a neurological disease may not be able to extricate themselves from such a situation. Another example is ‘cot death,’ where an infant gets wedged between the base and wall of the cot, causing respiratory distress. these types of traumatic asphyxial deaths are termed positional asphyxia.
Suffocation is used to describe death due to reduction of the concentration of oxygen in respired air. A reduction in atmospheric oxygen can occur in a decompressed aircraft cabin, an unused well or a grain silo. Reduction in the oxygen concentration of respired air can also occur due to mechanical causes like due to placing plastic bag around the head.
Postmortem examination reveals absence of classical signs of asphyxia. If the cause of obstruction is removed before examination, there may be no features attributable to death. This can also be seen in extremes of age, where the victim is intoxicated or unable to defend, and there may no signs of injuries on the body.
Suffocation is almost impossible to diagnose on post-mortem examination, if the offending object has been removed. However, as in most cases, homicidal deaths being masqueraded as natural or suicidal deaths tend to unravel following meticulous examination.
Smothering describes the physical obstruction of the nose and mouth to cause respiratory distress and death. While smothering usually leaves signs such as abrasions, contusion and lacerations of the inner aspect of the lips and cheeks, they may have no evidence of injury, including around the mouth or nose. This is commonly seen if the individual is unable to struggle, owing to extremes of age or intoxication, and if the object used is soft, like a pillow or scarf.
Frequently, examination will reveal intraoral injuries, including abrasions, contusions and lacerations of the lips or cheeks, especially the inner aspect, or contusion of the gums in edentulous individuals. Soft tissue of the face may reveal subcutaneous contusions around the mouth and nose. Fibers from the object may also be seen in and around the mouth and nose and may reveal the object used.
Smothering may also therefore be extremely difficult to diagnose at post-mortem examination. The items/objects alleged to have been used to smother, may have evidential value as it may have evidence that can be matched with the victim or the perpetrator. However, it should be remembered that common household items like pillows used by family members will tend to already be contaminated with their DNA and should be examined with caution. The value of evidence is of course far greater if matched with the perpetrator than with the victim.
NECK DISSECTION IN ANY DEATH AS A RESULT OF PRESSURE OVER NECK
Bloodless dissection of the neck is performed in all cases suspected to have resulted from pressure over the neck. The dissection starts with a midline incision from sternal notch, passing vertical downwards to end at pubis symphysis, sparing the umbilicus. Next, the scalp is incised at the coronal plan, extending between the mastoid processes on either side. The cranial cavity is emptied by delivering the brain, after the skull vault is opened. Similary, thoracic and abdominal cavities are emptied with evisceration of all thoracic and abdominal contents, from the neck downwards. For this, the trachea oesophagus and all connecting tissue of the neck are transected at the level of the sternal notch and the thoracic and abdominal blocs eviscerated by dissecting all posterior attachments. This technique helps to drain the blood from the neck structures, thereby assisting in unmasking injuries, especially contusion over the neck tissue.
Finally, after all three, cranial, thoracic and abdominal contents have been emptied, neck tissue is examined. An incision joining the coronal incision, from both mastoid processes, to the midline incision, at the sternal notch is made over the neck. The neck structures are then dissected layer by layer. At first, the skin over the neck is dissected from below up, till it reaches the lower border of mandible. The sterncleidoid muscles on both sides are dissected from its sternal and clavicular attachments and examined for injury. Similarly, the supra-hyoid and infra-hyoid group of muscles are dissected and examined for injury. The thyroid gland, laryngeal cartilage, hyoid bone and neck vessels should also be examined for any gross injuries. Lastly, the tongue is dissected from its attachments with a sub-mandibular approach and examined .