Abstract
Custody-related deaths are problematic. There clearly is a link between stress, exertion, restraint and SCD, but no consensus about causation, other than general agreement that most such deaths are multifactorial. The article by Krexi et al. in the January 26 issue of Medicine, Science and the Law 1 goes a long way towards untangling the possible factors and confounders to be considered by investigators. They are to be congratulated.
We were, however, disappointed to see the authors inappropriately elevate a case series to a causal relationship2,3 by accepting a now thoroughly defunct theory, one that was even retracted by its author while testifying at trial. 4 Specifically, Krexi states, ‘Restraint, especially in the face down position, leads to significant reduction in lung function’. In support of this position, she cites a 15-year-old case series by O’Halloran. The results lead many to believe that position-induced reductions in lung function are accepted fact. 5 They are not. O’Halloran’s case series was not a research study but rather a collection of partly complete case reports, useful for hypothesis generating but probative of nothing.
Fifteen years have passed since publication of the O’Halloran unblinded case series, and during that time a substantial number of blinded, peer-reviewed studies have shown that the prone position has relatively little impact on oxygenation. In 2007, Michaelwitz investigated the ventilatory and metabolic demands in healthy adults who had been placed in the prone maximal restraint position (PMRP). 6 Maximal voluntary ventilation (MVV) was measured in seated subjects (n = 30), in the PMRP (hogtied), and when prone with up to 90.1 or 102.3 kg of weight on their backs. MVV with >100 kg on their backs was 70% of the seated MVV (122 ± 28 and 156 ± 38 L/min, respectively; p < .001). However measurable decreases were observed in a second phase of the study when subjects were made to struggle vigorously before being studied; a decline in maximal minute ventilation (MMV) of 44% was observed. The researchers concluded the decrease in MVV was of no clinical importance in these subjects, and that even in PMRP ventilatory exchanges was still adequate to supply the ventilatory needs, a judgement that would be shared by any pulmonologist.
In 2012, Hall published her epidemiological study ‘Incidence and outcome of prone positioning following police use of force’. 7 In her study, data from a single police force serving >1.1 million people were collected for three consecutive years. Officers prospectively documented the final position of the subject, among other data points, via electronic study forms embedded in standard force reporting forms. Final resting position was available for 1255/1269 subjects. Force was required in 1269 cases. The majority (52%) were not even left in a prone position. There was one death, and that occurred in a prisoner not in the prone position. The authors concluded ‘prone positioning was common and was not associated with death in our cohort of consecutive subjects following police use of force’. 7 In 2014, Hall published her further study reporting 4828 consecutive force events in seven police agencies in four cities, concluding that their data support the human laboratory data that the prone position has no clinically significant effects on subject physiology. 8
In 2013, Savaser’s group evaluated the effect of maximal prone restraint (PMPR) 9 on a group aged 22–42 years old. Each volunteer was hogtied and tested in five different positions: supine, prone, prone maximal restraint with no weight force, prone maximal restraint with 50 lbs added to the subject’s back, and prone maximal restraint with 100 lbs added to the subject’s back for three minutes. Heart rate (HR), blood pressure (BP) and oxygenation saturation (O2 sat) were monitored for each volunteer in each position. In addition, echocardiography was performed to measure left ventricular outflow tract diameter. HR, MAP or O2 sat were statically no different in any of the positions.
In 2014, Sloane extended the work even further measuring the ventilatory and cardiovascular parameters in 10 intensely exercising volunteers (85% of their measured VO2 max) who were placed in PMPR after exercising and then studied while in three different positions for 15 minutes: (1) seated with hands behind the back, (2) prone with arms to the sides, and (3) PMPR position. 10 Cardiovascular parameters (oxygenation, stroke volume, inferior vena cava diameter, cardiac output, cardiac index, oxygenation, stroke volume, IVC diameter, cardiac output and cardiac index) were all measured. There was no evidence of hypoxia or hypoventilation during any of the monitored 15-minute position periods.
Numerous other papers confirm the findings summated above. Virtually everyone who investigates these deaths knows that SCD is due to a confluence of multiple causes, and we have passed the point where we need to invoke mysterious, impossible-to-prove temporal theories. Why negate the value of a lovely piece of pathology research by invoking what today could only be described as junk science.