Prone restraint cardiac arrest: A comprehensive review of the scientific literature and an explanation of the physiology

Deaths occurring among agitated or violent individuals subjected to physical restraint have been attributed to positional asphyxia. Restraint in the prone position has been shown to alter respiratory and cardiac physiology, although this is thought not to be to the degree that would cause asphyxia in a healthy, adult individual. This comprehensive review identifies and summarizes the current scientific literature on prone position and restraint, including experiments that assess physiology on individuals restrained in a prone position. Some of these experimental approaches have attempted to replicate situations in which prone restraint would be used. Overall, most findings revealed that individuals subjected to physical prone restraint experienced a decrease in ventilation and/or cardiac output (CO) in prone restraint. Metabolic acidosis is noted with increased physical activity, in restraint-associated cardiac arrest and simulated encounters. A decrease in ventilation and CO can significantly worsen acidosis and hemodynamics. Given these findings, deaths associated with prone physical restraint are not the direct result of asphyxia but are due to cardiac arrest secondary to metabolic acidosis compounded by inadequate ventilation and reduced CO. As such, the cause of death in these circumstances would be more aptly referred to as “prone restraint cardiac arrest” as opposed to “restraint asphyxia” or “positional asphyxia.”

Lethal mechanisms in cases of inverted suspension from the lap component of seat belts

A retrospective review of autopsy files at Forensic Science South Australia in Adelaide, Australia, was undertaken over a five-year period from January 2014 to December 2018 for all motor vehicle crashes with rollovers ending with the vehicle inverted and the occupants suspended by the lap component of their seat belts. There were five cases, all male drivers (aged 18–67 years; Mage = 32 years). Acute neck flexion or head wedging was noted in four cases, with facial petechiae in four and facial congestion in one. Deaths were due to positional asphyxia in four cases, with the combined effects of positional asphyxia and head trauma accounting for the remaining case. Although all drivers had evidence of head impact which may have caused incapacitation, in only one case was this considered severe enough to have contributed to death. A blood alcohol level above the legal limit for driving was detected in two cases, but no other drugs were detected. This series demonstrates another subset of cases of seat belt–associated deaths where suspension upside down by the lap component of a seat belt had occurred after vehicle rollovers. Predisposing factors include incapacitation of the victim and delay in rescue. The postulated lethal mechanism involved respiratory compromise from the weight of abdominal viscera on the diaphragm, as well as upper airway compromise due to kinking of the neck and wedging of the head.

Fatal positional asphyxia following a fall in bathroom

A 27-year-old female student was found dead inside the bathroom of her university hostel. The body was in a prone position with her neck over-flexed on to her trunk. The medico-legal autopsy found features of asphyxia. Multiple lacerated wounds were present on the occipital region of scalp. The cause of death was opined as positional asphyxia following an accidental fall and blunt trauma to the head. In this case, concussion due to blunt trauma to the head may have precluded any self-rescue efforts by the victim from the floor leading to positional asphyxia.