Positional Asphyxia

Positional asphyxia is a fatal condition owing to the body being oriented in an unusual position, either induced or adopted independently, which mechanically interferes with pulmonary ventilation by airway obstruction and interference of chest wall excursion (Fig. 62; refs. 416 and 417).

Ventilatory pump failure can be the result of decreased central respiratory drive (e.g., depressant drugs), chest wall defects (e.g., flail chest), and respiratory muscle fatigue (418). A victim may not be able to self-extricate from a position because of various factors (e.g., alcohol or other drugs, debilitation, degenerative brain disease [97, 99,246,418-420]). Alcohol and other drugs acting as CNS depressants relax muscles, including the tongue, causing airway obstruction (97,416). Toxic levels of these drugs also depress central respiratory centers. The CNS respiratory drive fails to respond to the increased biochemical demands of the body (417,419,421).

Variations of positional asphyxia have been described:

• Head-down position (reverse suspension, "upside-down;" see Fig. 63 and refs. 246, 416, 419, 420, and 422).

Fig. 61. Chronic aspiration. Foreign body granulomatous inflammation (vegetable material; H&E, magnification x200).
Positional Asphyxia
Fig. 62. Positional asphyxia.

° In contrast to the erect position, where thoracic breathing predominates, a person head-down has limited chest wall excursion (246,423-426). In cases of complete reverse suspension, the abdominal viscera press on the diaphragm, prolonging the inhalation phase (427). Initially, respiratory frequency increases to compensate (427).

Positional Asphyxia
Fig. 63. Positional asphyxia. Reverse suspension following vehicle rollover. (Courtesy of Dr. C. Rao, Regional Forensic Pathology Unit, Hamilton, Ontario, Canada.)

Eventually, hypoxia ensues because of the decrease in chest wall movement due to respiratory muscle fatigue (421,427). The decreased effectiveness of the respiratory muscles means the ability of intrathoracic pressure to allow effective venous return to the heart is reduced (246,425). Also, blood volume shifts to the head, where venous return to the heart is not as efficient (246). Diminished blood flow furthers respiratory muscle fatigue and eventually cardiac arrest occurs (425). ° The head-down position leads to death of rabbits in half a day (427). A decreased and often irregular pulse rate is observed in human volunteers (427). Estimates of time until death in humans (e.g., parachutists, occupants in a vehicle rollover) range from several hours to a day (246,419). ° The Trendelenburg position in the clinical setting has effects on cardiac and pulmonary function (419,427).

• Neck or trunk hyperflexion while head-down or sitting upright (e.g., neck hyperflexed occluding tracheostomy site; goiter occluding airway) leads to obstruction of the respiratory tract (416,417).

• Trunk flexed over object (e.g., edge of bathtub) restricting diaphragm and chest movement (48,417).

• Recreational abdominal suspension and compression (e.g., 12-yr-old girl suspended on swing by synthetic webbing [421 ]).

• Neck or chest compression (e.g., neck flexion from entrapment by bedrail; see Subheadings 2.1.4, 3.2., and 3.8. and refs. 99, 332, and 417).

• "Excited Delirium", "Prone Restraint Asphyxia" and the use of "Tasers."

° Deaths during prone restraint ("prone restraint asphyxia") arise when an individual becomes highly agitated ("excited delirium"), as a result of psychosis or stimulant drug intoxication (e.g. cocaine, hallucinogens, methamphetamine), and is subdued (428-431). These deaths occur in institutions and in the custody of police; therefore, they are problematic and controversial cases. During the delirium, individuals become paranoid, insensitive to pain and agitated (428,429,431,433). They possess "superhuman" strength, and a number of police officers are required to restrain and subdue them (429,431). Typically, these victims, after a preiod of considerable struggle, become quiet and then go into cardiorespiratory arrest (429,431,433). Various forms of restraint are employed, one variation of which is "hog-tying" or "hobbling" (417), which has been implicated as the primary cause of death. ° The events and phenomena leading up to deaths associated with prone restraint asphyxia are complicated and it essential that other causes of death, i.e. disease and trauma (e.g. head injury, neck compression, visceral injury) are excluded (430,431, 436). When faced with an apparent case of prone restraint asphyxia, several factors may have contributed to death (418,428-431,433,436-439): pressure may have been exerted on the neck (428,429,431); weight may have been applied to the chest wall (429); exhaustion, hypoxia, acidosis and hyperpyrexia may occur as a consequence of a prolonged struggle; alteration of brain receptor function in individuals who are chronic abusers of cocaine makes them prone to cocaine-induced excited delirium and hyperthermia (431-434); chronic cocaine use can lead to cardiomegaly and myocardial fibrosis, which are risk factors for an arrhythmia, the risk of which is potentiated by the "hyper-adrenaline" state of acute intoxication (418,431-433,435). In addition, it should be remembered that death can occur in unrestrained cases of excited delirium (432,433) or in individuals who are restrained in other than the "hog-tied" position (439a).

° The complexity of the various pre-mortem phenomena in fatal cases of prone restraint asphyxia prompted a series of experiments on human volunteers to determine the degree to which positioning of normal individuals in the "hog-tied" prone position after exercise interferes with the process of respiration, which relies on three critical processes (418): a patent airway; a "bellows" mechanism by which gases are moved into and out of the airways through the action of the ribs, intercostal muscles, diaphragm, abdominal wall and accessory muscles of respiration; and lungs in which there is a normal flow of gases into and out of the airspaces and across the alveolar walls to and from the pulmonary vasculature. Although the earliest of these studies suggested that the "hog-tied" position increased the recovery times of both heart rate and peripheral oxygen saturation after exercise (439b), these observations were refuted in a subsequent study that used more sophisticated methods for determining blood oxygenation and, in addition, which assessed pulmonary function (439). The latter study demonstrated that 'hog-tying" did produce a mild restrictive pulmonary deficit, to no less than 80% of normal predicted values, but this deficiency was not associated with hypoxia, hypercapnia or a delay in the post-exercise restitution of normal heart rate nor were the mild changes in pulmonary function any different from those occurring in unrestrained individuals who were lying supine or prone (418,439). The placement of up to 50 lbs of weight on the back did not further compromise respiratory function in additional studies on "hog-tied" healthy volunteers (435).

° The observations in healthy volunteers suggest that forcible restraint per se is not the sole cause of death in prone restraint asphyxia, leading to a commentary by Reay and Howard (418) that, in such causes, "causes of death are a matter of conjecture and cover the spectrum of catecholamine rush, neuroleptic malignant syndrome, psychogenic death (including exhaustive mania and excited delirium), and exercise induced cardiac arrest" or, in their other words, that "during the investigation [of prone restraint asphyxia] multiple factors emerge, all of which may have played some role in the death and none of which is convincing enough to stand alone as the undisputed cause of death." In such instances, Howard and Reay recommended that death is certified "by a descriptive statement that encompasses identified factors in the death" (418).

° As well as physical attempts at restraint, subjugation of individuals displaying excited delirium may also involve administration of pepper spray and electric shocks using a "taser", at times without apparent effect (428,429,431) (see Subheading 3.3.2.).

° A "taser" is a hand-held weapon ("neuromuscular incapacitation device") that uses a gunpowder charge to project two barbs, which remain tethered to the weapon by electric wires. When the barbs penetrate or lie in clothing close to, the skin, an incapacitating electric shock whose duration is controlled by the operator immobilizes the victim (439c-439f) and allows restraints to be placed. Several models of the taser weapon are, or have been, available, including the "original" Police model, a less powerful "public" model and a more recent advanced M26 model that is more effective at incapacitating individuals (439d).

° Tasers cause primary injuries, in the form of small puncture wounds and burns at the site of lodgement of the barbs or secondary injuries owing to falls caused by the incapacitating electric shock (439g). Rhabdomyolysis may also occur but its cause is uncertain because of the other potentially myotoxic factors that exist in many patients who are subjected by taser (see Chapter 8, Heading 13).

° Most deaths purported to be associated with the use of a taser have occurred minutes to hours after the electric shock and in individuals who are also intoxicated by phencyclidine (phenyl-cyclohexyl-piperidine [PCP]) (439g,439h) and/or cocaine (439g), both of which alone are capable of causing sudden death, or in cases who have pre-existing heart disease (439g). A prospective case study of all patients admitted to an Emergency Department over a five and a half year period who had been shot with a taser recorded 3 deaths in 218 patients; two cases developed a cardiac arrest 5 minutes and 15 minutes after being shot by a taser, and one case showed a respiratory then cardiac arrest 25 minutes after taser electrocution—all of the three cases had high serum and liver levels of PCP (439h). In addition, a case report describes a 16-year-old male who developed, and was resuscitated from, ventricular fibrillation after he had been shot by a taser, providing some evidence of a direct association between a taser electric shock and a potentially fatal cardiac dysrhythmia; however, the interval between the taser shooting and collapse of the patient is not recorded and the report does not state whether or not the victim was intoxicated by PCP, cocaine or other substance (439i). In contrast, analysis of the event record of an implantable defibrillator after a taser hit showed no evidence of ventricular fibrillation (439j).

° Experimental studies in pigs prove that the electrical charge required to induce ventricular fibrillation is directly related to body mass and is 15 to 42 times greater the charged delivered by the taser (439k). Studies on healthy human volunteers have shown no effect of taser discharges on cardiac activity at the time of, or 24 hours after, the electric shock (439l), in line with earlier observations showing no ECG abnormalities in patients treated in the Emergency Room after being shot by a taser (439h).

° The foregoing observations suggest that a taser strike, which delivers an electrical charge to the body, is, by itself, not a likely cause of death because of the immediacy of fatal collapse observed in typical electrocution deaths (see Chapter 4, Subheading 7.1.4.). Nevertheless, it is almost impossible to prove (or refute) the extent to which an electric shock, delivered by a taser to an individual in a state of physiological or toxicological "excited delirium", is the immediate cause of death, a problem reminiscent of the difficulties in deciding which of the many factors cause death in prone restraint asphyxia, as discussed previouly in this section. There is some justification, therefore, for the comment that "...while the use of tasers may be generally safe in healthy adults, preexisting heart disease, psychosis and the use of drugs... may substantially increase the risk of fatality." (439m)

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