http://www.jfsmonline.com/article.asp?issn=2349-5014;year=2018;volume=4;issue=4;spage=233;epage=237;aulast=Cao
Death caused by compression of the neck, such as from hanging, strangling, or throttling, is termed "mechanical asphyxia" and usually has obvious physical findings. However, asphyxias that result from no direct pressure on the neck vessels or trachea, lack typical morphological changes, or result in minimal damage are called "subtle asphyxias"[1] or "atypical mechanical asphyxias," used in this article. Atypical mechanical asphyxias include smothering, choking, environmental hypoxia, traumatic asphyxia, and positional asphyxia, among others.
Smothering is a form of asphyxia death caused by obstructing the mouth and nose with hands, airtight papers, soft textiles, or the weight of one's own head.[2]
Smothering can be seen in homicidal or suicidal cases. Homicidal smothering is common in infants, older adults, and people who are unconscious or have restricted motion due to fabric bundling, disease, poisoning, or intoxication. Homicidal smothering can also result when there are significant physical power differences between a perpetrator and victim.[3],[4],[5] Suicidal smothering is common in psychiatric patients; an example includes wrapping tape around one's mouth, nose, or the entire face.[6] Smothering can also occur accidentally. For example, adults who are unconscious or paralyzed because of drunkenness, epilepsy, drug overdose, or having another disease might accidentally asphyxiate themselves. Similarly, for an infant lying face down on an airtight mattress or pillow, the weight of the infant's head might obstruct, distort, and occlude his or her mouth and nose, leading to suffocation. In a third example, sleeping infants with clothes or bedding covering their faces are at an increased risk of suffocation.[1],[2]
In general, it is difficult to identify a case of smothering during forensic scene examination because physical findings are nonspecific.[7],[8] If smothering is suspected, there may be local signs of pressure on the face.[2],[3] In adults, with even slight resistance, signs include skin exfoliation from fingernails; contusions on the nose, cheeks, or chin from fingers; bleeding and skin tears corresponding to the teeth in the oral mucosa; and intramuscular bleeding at the mandibular margin. Nasal deformation is also considered a sign of smothering, but can be caused by emergency tracheal intubation.[3],[5],[7] In infants and adults who are unable to physically resist during asphyxiation, physical damage is difficult to detect.[3] Of note, a body in the prone position concentrates pressure on the face, preventing accumulation of blood into the compressed skin around the mouth and nose, leading to the formation of distinct pale areas caused by the absence of pooled blood. It is, therefore, important not to assume that pale areas such as these have resulted from indentation by smothering.[2]
Without positive physical findings in smothering cases, scene investigation plays a decisive role. Pillows and bedding should be examined for blood or lipstick.[5],[9] For suspected cases of smothering, even if postmortem changes are obvious, suspicious skin lesions should be biopsied for histological examination.[5] In cases of smothering by textiles, the mouth, nasal cavity, and airways should be examined for inhaled fabric fibers. Fibers in the trachea indicate that a patient may have been alive during smothering.[8]
Gagging generally involves placing fabric in a victim's mouth to prevent yelling; the fabric gradually becomes soaked with saliva, and if airtight, will lead to suffocation. Another form of gagging involves placing tape over the mouth or nose, which results in trapped mucus production that eventually leads to suffocation. Obstruction of the nasopharynx by objects in the oral cavity may also lead to gagging and subsequent death.[2] Usually, suspected gagging is confirmed when blocking objects are found, not by any specific physical signs of asphyxia.[3]
Choking refers to upper respiratory tract blockage by a foreign body leading to suffocation. The foreign body is usually lodged between the larynx and trachea.[10],[11] Death may result from simple hypoxia; however, many deaths occur quickly before the onset of hypoxia. Studies have found that, even in cases in which the airway is not completely blocked, death often occurs, likely from neurogenic-induced cardiac arrest.[2],[9],[11],[12]
Choking is almost always accidental, with cases of homicide and suicide relatively rare.[1],[11] For infants, accidental choking most often occurs with foreign body ingestion; for adults, choking most often occurs with food.[1],[11] Victims in homicidal choking cases are most likely to be older adults, infants, young children, people who are unconscious, or persons debilitated by illness or intoxication. Suicidal choking most often occurs in patients with psychosis or prisoners in jail.[1]
Evidence of coughing helps eliminate choking as a cause of death because it signifies that the respiratory tract was open during upper respiratory blockage.[3] Computed tomography imaging can provide information before an autopsy on the location of a foreign body and can help inform an autopsy plan.[13] Few physical findings are generally seen in choking deaths, so the discovery of a foreign body in the airway, a detailed clinical history, descriptions of the death environment and any resuscitation attempts, and exclusion of other causes of death are critical when forming a conclusion.[1],[9],[11],[12] If the foreign body shifts during resuscitation or otherwise is moved, clinical history might be the only evidence.[3],[13]
Foreign bodies blocking the airway leading to choking generally belong to the following categories.[2]
Foreign objects
Attackers may put a towel or sock into the victim's mouth to prevent shouting; this can cause choking and gagging.[3] In another example, people may inhale sand, piles of gravel, or piles of soil when they fall on them, causing respiratory blockage and resulting in choking death. This scenario may occur accidentally at a construction site, during a traffic accident, or in children playing in or eating sand.[3],[14]
Acute obstruction
Acute allergy, steam stimulation, heat inhalation, and acute inflammation may cause swelling of the throat organs, including the epiglottis, tonsils, or glottis, leading to choking. Trauma in the anterior or lateral cervical neck structures can also result in severe swelling of the respiratory tract from bleeding and edema.[1],[2],[7] Tumors, polyps, or cysts can also block respiration, leading to choking.[1],[10],[11]
Foods
The most common foreign bodies causing choking death in adults are foods.[10] Susceptible factors include old age, neuromuscular disease, poor dentition leading to chewing problems, consumption of alcohol or other central nervous system depressants weakening the gag reflex, or other neurological or mental illness (of which poor dentition is an important risk factor).[1],[11],[12],[13] Of patients with mental illness, those with schizophrenia are most likely to choke on food, possibly from a propensity to swallow incompletely chewed food.[11] The majority of adult choking cases occur at patients' homes, nursing homes, or mental hospitals, and often take place suddenly during meals.[1]
When a sudden death occurs while eating or soon after, the possibility of choking must be considered. A search for a blocked airway should be initiated, but in addition, the investigator should also consider factors that could have aggravated the choking episode. Therefore, quality and number of teeth, food debris in the esophagus – which can cause tracheal obstruction from the external oppression – and exclusion of neurological diseases and intoxication are all important when evaluating sudden death during a meal.[1],[9],[11],[12]
It is typical for gastric contents to be present in the throat, trachea, and bronchi after death, caused by reflux or shifting of contents. This is a common postmortem phenomenon, found in 20%–25% of routine examinations. As a result, if a small amount of gastric content is found in the respiratory tract, this does not mean that choking had occurred; however, if the throat or airway is completely blocked by gastric contents, choking can be concluded.[2],[3],[13] The inhalation of gastric contents is more common in people who are unconscious.[1]Importantly, there is no reliable way to distinguish natural food reflux early in the dying process from true inhalation while alive, unless the inhalation occurred during a clinical procedure or another person witnessed the event. In most cases, in the absence of hard evidence, it is unreasonable for forensic officers to conclude that the inhalation of gastric contents is secondary to choking death.[2]
Environmental asphyxiation is usually caused by a lack of oxygen in the local environment,[1],[2],[3] and is almost always accidental. Oxygen deficiency can occur secondary to breathing exercises, microbial consumption, activities related to industrial work (such as welding), environmental chemical reactions (such as rust), absorption by chemical substances (such as activated carbon), and presence of toxic gases (such as propane, nitrogen, and methane).[1],[2],[3] An atmospheric oxygen concentration below 5%–10% will cause death in a few minutes, and a concentration of carbon dioxide higher than 10% is lethal.[1] In some cases, death occurs before the onset of hypoxia, and is secondary to overexcitement of the body's chemical sensing system, which causes parasympathetic nervous system-mediated cardiac arrest.[2]
In hypoxia-asphyxia deaths caused by low atmospheric oxygen levels, physical findings are usually absent,[2] making elucidation of the specific cause of death difficult. Investigators must carefully analyze the environment and exclude other causes of death to conclude environmental hypoxia-asphyxia.[3] Measurements of toxic gases and oxygen concentrations in the air, as well as postmortem analysis of blood and tissues, should be performed; in addition, scene simulations may be required.[1]
As a type of environmental hypoxia-asphyxia, plastic bag suffocation is often used as a suicide technique in Western countries. This method is common in young men and elderly women.[15] Some people even use the propane, ether, or helium gas along with the plastic bag. Plastic bag suffocation deaths can also occur accidentally or unexpectedly, such as during sexual asphyxia, children playing with plastic bags, and other occurrences.[1] It is very rare for the use of plastic bags to result in death; however, it is more likely in cases in which the victim is unconscious, or when there is a large difference in strength between the perpetrator and victim.[16]
Plastic bag suffocation often occurs rapidly with few physical signs;[1],[2] however, in a small number of cases, marks on the neck are present corresponding to the areas of bag bundling (such as from a rubber band), or there may be signs of prior injury, such as wrist cutting or abuse.[1],[2] It is a common misconception that the postmortem presence of moisture in the plastic bag confirms that the bag was placed on a breathing human; water droplets form as gas evaporates from the skin, nose, and mouth even if the person was previously deceased.[2]
Because there are usually no specific physical findings, it is difficult to identify cases of plastic bag suffocation unless the bag is over the head at the time of scene investigation or autopsy.[2] If the plastic bag is removed before forensic workers see the corpse, they will not be able to determine the cause of death through forensic examination, and may even conclude that a natural death occurred. Therefore, to identify such cases, forensic workers must pay careful attention during scene exploration and investigation.[1],[3],[9],[16] If necessary, forensic workers can conduct simulations under close monitoring in a protected environment, which can help to pinpoint a cause of death through analysis of time measurements.[4],[6],[17] Specimens collected from the blood, lungs, liver, or other organs for poison analysis should be extracted and stored in a sealed empty bottle along with a plastic bag,[2],[7],[16] frozen, and delivered promptly.[1]
Traumatic asphyxia refers to the compression of the chest or abdomen by massive mechanical forces resulting in thoracic fixation – expansion of thoracic and lower phrenic muscles – leading to respiratory disturbance and death by asphyxiation.[2]
Traumatic asphyxia is common in the following types of accidents: motor vehicle compression or extrusion during traffic accidents; pinning from building collapse, falling rocks, or other objects; trampling by a crowd; compression while standing in a crowded population from sudden external forces; compression by fallen tools or furniture; and compression of infants and children while sleeping with parents (overlaying asphyxia).[1],[2],[18] There are also reports of homicide resulting from a perpetrator kneeling or sitting on the chest of a victim.[19]
The pathological features of traumatic asphyxia are usually quite specific. These include prominent facial and nuchal hyperemia and swelling; numerous petechial hemorrhages on the face or conjunctiva; subconjunctival hemorrhage and edema; and nasal bleeding. In general, a person who dies from traumatic asphyxiation often appears strangled with features extending down to the neck, with no signs of local damage.[2],[20],[21]
However, physical features such as these are not always visible. Studies have shown that, in up to 10% of cases, no petechial hemorrhages are seen on the face or conjunctiva. The reason for this is unclear, but may be related to rapidness of death, lack of obvious chest compression or vagus nerve stimulation, lack of occlusion of the epiglottis, or concurrence of both left heart and right heart impairment at the time of chest compression.[1],[18],[20],[21] On gross examination, lungs may have a purplish red color, congestion, or subserous bleeding with or without obvious expansion of the right heart or superior vena cava; sometimes, there is no evidence of trauma despite severe direct external compression on the chest and abdomen.[1],[2],[3],[9]
Traumatic asphyxia is a diagnosis of exclusion. In addition to supporting evidence from a scene investigation, suffocation death should only be considered after excluding fatal injuries and poisoning.[1],[9],[21]
Overlaying asphyxia is a special form of traumatic asphyxia, often secondary to nasal compression. Physical examination findings are usually absent, so overlaying can be difficult to determine unless the same-bed sleeper admits to crushing the infant or child. Overlaying asphyxia is sometimes attributed to sudden infant death syndrome, so it is important to examine adults' and children's clothes and bedding carefully as well as the scene.[1],[3],[22]
Positional asphyxia refers occurrences in which respiration is compromised from splinting of the chest or diaphragm preventing normal respiration, or occlusion of the upper airway due to abnormal positioning of the body.[23] Positional asphyxia is almost always an accident, during which the victim cannot extract himself or herself from a specific position or small space. The victim may be further impaired by alcohol or drug intoxication, weakness, neurological disease, or fabric bundling. Common examples of positional asphyxia include limbs tied behind the back while in a prone position (may be performed for restraint by police or psychiatrists for suspects or patients); head-down position (inversion of the body, or head hanging down off the edge of a bathtub); jack-knife position (upper body significantly curved from the waist down); bundled thoracic or abdominal horizontal sling (e.g., a young girl wearing a belt hanging by the abdomen on a swing); excessive flexion or extension of the neck (e.g., during a motor vehicle accident); lack of chest wall expansion in a restricted space (wedging); and a person sandwiched between the wall and the mattress after falling off the bed.[1],[2],[3],[4],[5],[6],[7],[24] A typical case of postural asphyxia involves a drunken person who collapses into a narrow space, excessively distorting the neck and hindering breathing, leading to death.[9]
Cause of death from positional asphyxia often results from reverse suspension of the body such that the movement of the chest wall is restricted by intra-abdominal organs compressing the diaphragm. This prolongs inspiration, and eventually results in respiratory muscle fatigue, leading to slowed movement of the chest wall and subsequent hypoxia. Venous return is effectively limited, and blood flow to the brain is shifted, decreasing blood flow and further aggravating respiratory muscle fatigue; eventually, the heart stops.[1] Positional asphyxia does not require reversal of the entire body; fatal asphyxia may result from the reversal of torso position, excessive flexion of the neck, or pressure on one's face, such as in an intoxicated person whose face is pressed to the floor.[25] The difference between traumatic asphyxia and positional asphyxia is whether the chest and abdomen are compressed by external forces. If chest compression is from an external source, he or she should have been died from traumatic asphyxia. If a deceased person is found in a specific position or restricted space that limits chest activity, the person should have been died from positional asphyxia.[1],[23]
Positional asphyxia can be identified by the following criteria: The body position is consistent with restricted or disordered respiration; scene investigation or historical investigation identifies that an accident had occurred; the deceased person cannot change his or her position for some reason; and other obvious natural or violent causes of death are excluded. A diagnosis of accidental positional asphyxia mainly depends on the evidence obtained from the scene environment.[24],[25] Some forensic investigators believe that, if another disease is present, then either the cause of death is not associated with positional asphyxia, or the onset of the disease makes the deceased patient prone to positional asphyxia.[23] It should be noted that alcohol consumed by a patient with positional asphyxia may be metabolized. Thus, even if the concentration of alcohol in the blood or urine is very low or negative, the possibility of positional asphyxia cannot be ignored.[24]
Wedging is a special form of positional asphyxia, commonly seen in infants and young children whose body or head are compressed in a narrow space. The chest wall is fixed, resulting in airway obstruction that results in asphyxia. Wedging usually occurs between a mattress and wall or mattress and furniture or baby crib. It is most common in infants aged 3–6 months, intoxicated adults, or comatose patients who accidentally fall between a mattress and wall, leading to death. Physical findings of wedging are usually absent.[1],[22]
Acknowledgments
This study was supported by the Open Project of Key Laboratory of Forensic Genetics, Ministry of Public Security (2017FGKFKT05), Program for Young Innovative Research Team from China University of Political Science and Law (2016CXTD05), and Project of Interdisciplinary Science Construction-Forensic Psychology from China University of Political Science and Law.
Forensic investigation of atypical asphysia
Zhe Cao1, Zhiyuan An2, Xiaoning Hou1, Dong Zhao3
1 Anshan Public Security Bureau, Anshan, China
2 Key Laboratory of Evidence Science (China University of Political Science and Law), Ministry of Education, China, Collaborative Innovation Center of Judicial Civilization, China
3 Key Laboratory of Evidence Science (China University of Political Science and Law), Ministry of Education, China, Collaborative Innovation Center of Judicial Civilization; Key Laboratory of Forensic Genetics of Ministry of Public Security, Institute of Forensic Science, Ministry of Public Security, Beijing, China
Correspondence Address:
Dr. Dong Zhao
25 Xitucheng Road, Haidian, Beijing 100088
China
| Abstract |
Smothering, choking, confined spaces, traumatic asphyxia, positional asphyxia, and other kinds of atypical mechanical asphyxia are not rare in forensic practice. However, these are not commonly well demonstrated in forensic monographs worldwide. The authors researched related works and literatures and summarized these with a view to contribute to the existing teaching resources and provide help to forensic practitioners who are involved in scene investigation and identification of such deaths.
Keywords: Asphyxia, forensic pathology, forensic medicine
| Introduction |  |
Death caused by compression of the neck, such as from hanging, strangling, or throttling, is termed "mechanical asphyxia" and usually has obvious physical findings. However, asphyxias that result from no direct pressure on the neck vessels or trachea, lack typical morphological changes, or result in minimal damage are called "subtle asphyxias"[1] or "atypical mechanical asphyxias," used in this article. Atypical mechanical asphyxias include smothering, choking, environmental hypoxia, traumatic asphyxia, and positional asphyxia, among others.
| Smothering | |
Smothering is a form of asphyxia death caused by obstructing the mouth and nose with hands, airtight papers, soft textiles, or the weight of one's own head.[2]
Smothering can be seen in homicidal or suicidal cases. Homicidal smothering is common in infants, older adults, and people who are unconscious or have restricted motion due to fabric bundling, disease, poisoning, or intoxication. Homicidal smothering can also result when there are significant physical power differences between a perpetrator and victim.[3],[4],[5] Suicidal smothering is common in psychiatric patients; an example includes wrapping tape around one's mouth, nose, or the entire face.[6] Smothering can also occur accidentally. For example, adults who are unconscious or paralyzed because of drunkenness, epilepsy, drug overdose, or having another disease might accidentally asphyxiate themselves. Similarly, for an infant lying face down on an airtight mattress or pillow, the weight of the infant's head might obstruct, distort, and occlude his or her mouth and nose, leading to suffocation. In a third example, sleeping infants with clothes or bedding covering their faces are at an increased risk of suffocation.[1],[2]
In general, it is difficult to identify a case of smothering during forensic scene examination because physical findings are nonspecific.[7],[8] If smothering is suspected, there may be local signs of pressure on the face.[2],[3] In adults, with even slight resistance, signs include skin exfoliation from fingernails; contusions on the nose, cheeks, or chin from fingers; bleeding and skin tears corresponding to the teeth in the oral mucosa; and intramuscular bleeding at the mandibular margin. Nasal deformation is also considered a sign of smothering, but can be caused by emergency tracheal intubation.[3],[5],[7] In infants and adults who are unable to physically resist during asphyxiation, physical damage is difficult to detect.[3] Of note, a body in the prone position concentrates pressure on the face, preventing accumulation of blood into the compressed skin around the mouth and nose, leading to the formation of distinct pale areas caused by the absence of pooled blood. It is, therefore, important not to assume that pale areas such as these have resulted from indentation by smothering.[2]
Without positive physical findings in smothering cases, scene investigation plays a decisive role. Pillows and bedding should be examined for blood or lipstick.[5],[9] For suspected cases of smothering, even if postmortem changes are obvious, suspicious skin lesions should be biopsied for histological examination.[5] In cases of smothering by textiles, the mouth, nasal cavity, and airways should be examined for inhaled fabric fibers. Fibers in the trachea indicate that a patient may have been alive during smothering.[8]
Gagging generally involves placing fabric in a victim's mouth to prevent yelling; the fabric gradually becomes soaked with saliva, and if airtight, will lead to suffocation. Another form of gagging involves placing tape over the mouth or nose, which results in trapped mucus production that eventually leads to suffocation. Obstruction of the nasopharynx by objects in the oral cavity may also lead to gagging and subsequent death.[2] Usually, suspected gagging is confirmed when blocking objects are found, not by any specific physical signs of asphyxia.[3]
| Choking | |
Choking refers to upper respiratory tract blockage by a foreign body leading to suffocation. The foreign body is usually lodged between the larynx and trachea.[10],[11] Death may result from simple hypoxia; however, many deaths occur quickly before the onset of hypoxia. Studies have found that, even in cases in which the airway is not completely blocked, death often occurs, likely from neurogenic-induced cardiac arrest.[2],[9],[11],[12]
Choking is almost always accidental, with cases of homicide and suicide relatively rare.[1],[11] For infants, accidental choking most often occurs with foreign body ingestion; for adults, choking most often occurs with food.[1],[11] Victims in homicidal choking cases are most likely to be older adults, infants, young children, people who are unconscious, or persons debilitated by illness or intoxication. Suicidal choking most often occurs in patients with psychosis or prisoners in jail.[1]
Evidence of coughing helps eliminate choking as a cause of death because it signifies that the respiratory tract was open during upper respiratory blockage.[3] Computed tomography imaging can provide information before an autopsy on the location of a foreign body and can help inform an autopsy plan.[13] Few physical findings are generally seen in choking deaths, so the discovery of a foreign body in the airway, a detailed clinical history, descriptions of the death environment and any resuscitation attempts, and exclusion of other causes of death are critical when forming a conclusion.[1],[9],[11],[12] If the foreign body shifts during resuscitation or otherwise is moved, clinical history might be the only evidence.[3],[13]
Foreign bodies blocking the airway leading to choking generally belong to the following categories.[2]
Foreign objects
Attackers may put a towel or sock into the victim's mouth to prevent shouting; this can cause choking and gagging.[3] In another example, people may inhale sand, piles of gravel, or piles of soil when they fall on them, causing respiratory blockage and resulting in choking death. This scenario may occur accidentally at a construction site, during a traffic accident, or in children playing in or eating sand.[3],[14]
Acute obstruction
Acute allergy, steam stimulation, heat inhalation, and acute inflammation may cause swelling of the throat organs, including the epiglottis, tonsils, or glottis, leading to choking. Trauma in the anterior or lateral cervical neck structures can also result in severe swelling of the respiratory tract from bleeding and edema.[1],[2],[7] Tumors, polyps, or cysts can also block respiration, leading to choking.[1],[10],[11]
Foods
The most common foreign bodies causing choking death in adults are foods.[10] Susceptible factors include old age, neuromuscular disease, poor dentition leading to chewing problems, consumption of alcohol or other central nervous system depressants weakening the gag reflex, or other neurological or mental illness (of which poor dentition is an important risk factor).[1],[11],[12],[13] Of patients with mental illness, those with schizophrenia are most likely to choke on food, possibly from a propensity to swallow incompletely chewed food.[11] The majority of adult choking cases occur at patients' homes, nursing homes, or mental hospitals, and often take place suddenly during meals.[1]
When a sudden death occurs while eating or soon after, the possibility of choking must be considered. A search for a blocked airway should be initiated, but in addition, the investigator should also consider factors that could have aggravated the choking episode. Therefore, quality and number of teeth, food debris in the esophagus – which can cause tracheal obstruction from the external oppression – and exclusion of neurological diseases and intoxication are all important when evaluating sudden death during a meal.[1],[9],[11],[12]
It is typical for gastric contents to be present in the throat, trachea, and bronchi after death, caused by reflux or shifting of contents. This is a common postmortem phenomenon, found in 20%–25% of routine examinations. As a result, if a small amount of gastric content is found in the respiratory tract, this does not mean that choking had occurred; however, if the throat or airway is completely blocked by gastric contents, choking can be concluded.[2],[3],[13] The inhalation of gastric contents is more common in people who are unconscious.[1]Importantly, there is no reliable way to distinguish natural food reflux early in the dying process from true inhalation while alive, unless the inhalation occurred during a clinical procedure or another person witnessed the event. In most cases, in the absence of hard evidence, it is unreasonable for forensic officers to conclude that the inhalation of gastric contents is secondary to choking death.[2]
| Environmental Hypoxia | |
Environmental asphyxiation is usually caused by a lack of oxygen in the local environment,[1],[2],[3] and is almost always accidental. Oxygen deficiency can occur secondary to breathing exercises, microbial consumption, activities related to industrial work (such as welding), environmental chemical reactions (such as rust), absorption by chemical substances (such as activated carbon), and presence of toxic gases (such as propane, nitrogen, and methane).[1],[2],[3] An atmospheric oxygen concentration below 5%–10% will cause death in a few minutes, and a concentration of carbon dioxide higher than 10% is lethal.[1] In some cases, death occurs before the onset of hypoxia, and is secondary to overexcitement of the body's chemical sensing system, which causes parasympathetic nervous system-mediated cardiac arrest.[2]
In hypoxia-asphyxia deaths caused by low atmospheric oxygen levels, physical findings are usually absent,[2] making elucidation of the specific cause of death difficult. Investigators must carefully analyze the environment and exclude other causes of death to conclude environmental hypoxia-asphyxia.[3] Measurements of toxic gases and oxygen concentrations in the air, as well as postmortem analysis of blood and tissues, should be performed; in addition, scene simulations may be required.[1]
As a type of environmental hypoxia-asphyxia, plastic bag suffocation is often used as a suicide technique in Western countries. This method is common in young men and elderly women.[15] Some people even use the propane, ether, or helium gas along with the plastic bag. Plastic bag suffocation deaths can also occur accidentally or unexpectedly, such as during sexual asphyxia, children playing with plastic bags, and other occurrences.[1] It is very rare for the use of plastic bags to result in death; however, it is more likely in cases in which the victim is unconscious, or when there is a large difference in strength between the perpetrator and victim.[16]
Plastic bag suffocation often occurs rapidly with few physical signs;[1],[2] however, in a small number of cases, marks on the neck are present corresponding to the areas of bag bundling (such as from a rubber band), or there may be signs of prior injury, such as wrist cutting or abuse.[1],[2] It is a common misconception that the postmortem presence of moisture in the plastic bag confirms that the bag was placed on a breathing human; water droplets form as gas evaporates from the skin, nose, and mouth even if the person was previously deceased.[2]
Because there are usually no specific physical findings, it is difficult to identify cases of plastic bag suffocation unless the bag is over the head at the time of scene investigation or autopsy.[2] If the plastic bag is removed before forensic workers see the corpse, they will not be able to determine the cause of death through forensic examination, and may even conclude that a natural death occurred. Therefore, to identify such cases, forensic workers must pay careful attention during scene exploration and investigation.[1],[3],[9],[16] If necessary, forensic workers can conduct simulations under close monitoring in a protected environment, which can help to pinpoint a cause of death through analysis of time measurements.[4],[6],[17] Specimens collected from the blood, lungs, liver, or other organs for poison analysis should be extracted and stored in a sealed empty bottle along with a plastic bag,[2],[7],[16] frozen, and delivered promptly.[1]
| Traumatic Asphyxia | |
Traumatic asphyxia refers to the compression of the chest or abdomen by massive mechanical forces resulting in thoracic fixation – expansion of thoracic and lower phrenic muscles – leading to respiratory disturbance and death by asphyxiation.[2]
Traumatic asphyxia is common in the following types of accidents: motor vehicle compression or extrusion during traffic accidents; pinning from building collapse, falling rocks, or other objects; trampling by a crowd; compression while standing in a crowded population from sudden external forces; compression by fallen tools or furniture; and compression of infants and children while sleeping with parents (overlaying asphyxia).[1],[2],[18] There are also reports of homicide resulting from a perpetrator kneeling or sitting on the chest of a victim.[19]
The pathological features of traumatic asphyxia are usually quite specific. These include prominent facial and nuchal hyperemia and swelling; numerous petechial hemorrhages on the face or conjunctiva; subconjunctival hemorrhage and edema; and nasal bleeding. In general, a person who dies from traumatic asphyxiation often appears strangled with features extending down to the neck, with no signs of local damage.[2],[20],[21]
However, physical features such as these are not always visible. Studies have shown that, in up to 10% of cases, no petechial hemorrhages are seen on the face or conjunctiva. The reason for this is unclear, but may be related to rapidness of death, lack of obvious chest compression or vagus nerve stimulation, lack of occlusion of the epiglottis, or concurrence of both left heart and right heart impairment at the time of chest compression.[1],[18],[20],[21] On gross examination, lungs may have a purplish red color, congestion, or subserous bleeding with or without obvious expansion of the right heart or superior vena cava; sometimes, there is no evidence of trauma despite severe direct external compression on the chest and abdomen.[1],[2],[3],[9]
Traumatic asphyxia is a diagnosis of exclusion. In addition to supporting evidence from a scene investigation, suffocation death should only be considered after excluding fatal injuries and poisoning.[1],[9],[21]
Overlaying asphyxia is a special form of traumatic asphyxia, often secondary to nasal compression. Physical examination findings are usually absent, so overlaying can be difficult to determine unless the same-bed sleeper admits to crushing the infant or child. Overlaying asphyxia is sometimes attributed to sudden infant death syndrome, so it is important to examine adults' and children's clothes and bedding carefully as well as the scene.[1],[3],[22]
| Positional Asphyxia | |
Positional asphyxia refers occurrences in which respiration is compromised from splinting of the chest or diaphragm preventing normal respiration, or occlusion of the upper airway due to abnormal positioning of the body.[23] Positional asphyxia is almost always an accident, during which the victim cannot extract himself or herself from a specific position or small space. The victim may be further impaired by alcohol or drug intoxication, weakness, neurological disease, or fabric bundling. Common examples of positional asphyxia include limbs tied behind the back while in a prone position (may be performed for restraint by police or psychiatrists for suspects or patients); head-down position (inversion of the body, or head hanging down off the edge of a bathtub); jack-knife position (upper body significantly curved from the waist down); bundled thoracic or abdominal horizontal sling (e.g., a young girl wearing a belt hanging by the abdomen on a swing); excessive flexion or extension of the neck (e.g., during a motor vehicle accident); lack of chest wall expansion in a restricted space (wedging); and a person sandwiched between the wall and the mattress after falling off the bed.[1],[2],[3],[4],[5],[6],[7],[24] A typical case of postural asphyxia involves a drunken person who collapses into a narrow space, excessively distorting the neck and hindering breathing, leading to death.[9]
Cause of death from positional asphyxia often results from reverse suspension of the body such that the movement of the chest wall is restricted by intra-abdominal organs compressing the diaphragm. This prolongs inspiration, and eventually results in respiratory muscle fatigue, leading to slowed movement of the chest wall and subsequent hypoxia. Venous return is effectively limited, and blood flow to the brain is shifted, decreasing blood flow and further aggravating respiratory muscle fatigue; eventually, the heart stops.[1] Positional asphyxia does not require reversal of the entire body; fatal asphyxia may result from the reversal of torso position, excessive flexion of the neck, or pressure on one's face, such as in an intoxicated person whose face is pressed to the floor.[25] The difference between traumatic asphyxia and positional asphyxia is whether the chest and abdomen are compressed by external forces. If chest compression is from an external source, he or she should have been died from traumatic asphyxia. If a deceased person is found in a specific position or restricted space that limits chest activity, the person should have been died from positional asphyxia.[1],[23]
Positional asphyxia can be identified by the following criteria: The body position is consistent with restricted or disordered respiration; scene investigation or historical investigation identifies that an accident had occurred; the deceased person cannot change his or her position for some reason; and other obvious natural or violent causes of death are excluded. A diagnosis of accidental positional asphyxia mainly depends on the evidence obtained from the scene environment.[24],[25] Some forensic investigators believe that, if another disease is present, then either the cause of death is not associated with positional asphyxia, or the onset of the disease makes the deceased patient prone to positional asphyxia.[23] It should be noted that alcohol consumed by a patient with positional asphyxia may be metabolized. Thus, even if the concentration of alcohol in the blood or urine is very low or negative, the possibility of positional asphyxia cannot be ignored.[24]
Wedging is a special form of positional asphyxia, commonly seen in infants and young children whose body or head are compressed in a narrow space. The chest wall is fixed, resulting in airway obstruction that results in asphyxia. Wedging usually occurs between a mattress and wall or mattress and furniture or baby crib. It is most common in infants aged 3–6 months, intoxicated adults, or comatose patients who accidentally fall between a mattress and wall, leading to death. Physical findings of wedging are usually absent.[1],[22]
Acknowledgments
This study was supported by the Open Project of Key Laboratory of Forensic Genetics, Ministry of Public Security (2017FGKFKT05), Program for Young Innovative Research Team from China University of Political Science and Law (2016CXTD05), and Project of Interdisciplinary Science Construction-Forensic Psychology from China University of Political Science and Law.
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