Issues and Findings
Discussed in this Brief: The effect of oleoresin
capsicum (OC), or pepper
spray, on respiration, particularly when combined with positional
restraint.
Researchers exposed 34 subjects to OC spray, both while sitting and
in the
prone maximal restraint position.
Key issues: OC spray has gained wide acceptance in law enforcement
as a
swift and effective way to subdue violent and dangerous suspects in
the
field with relatively little force. As its use has increased, however,
OC
spray has been associated in the media with the deaths of a number
of
suspects in custody. Some have argued that OC spray, when used in
combination with physical restraints, can lead to significant respiratory
compromise, including asphyxiation and death. To test this theory,
researchers examined the respiratory effects of inhaling OC spray
while in
the sitting and restraint positions and compared the results with
those
obtained in the same two positions when subjects inhaled a placebo
spray.
Key findings: OC exposure and inhalation do not result in a significant
risk for respiratory compromise or asphyxiation, even when combined
with positional restraint.
o In the sitting position, OC spray inhalation and exposure resulted
in no
respiratory compromise. There was no evidence of abnormally low oxygen
levels or abnormally high levels of carbon dioxide (CO2). In fact,
the
lower CO2 levels for this group suggest that OC spray may actually
increase ventilation slightly.
o Researchers detected no difference between the OC and placebo groups
in the restraint position. There was some decline in pulmonary function,
but not enough to be clinically significant. As in the sitting position,
OC
seemed to increase ventilation.
o OC exposure did, however, result in an increase in blood pressure,
perhaps due to the discomfort and pain associated with OC. The clinical
implications of this finding remain unknown.
o This study had a number of limitations. First, not all of the conditions
that occur when OC and restraint are employed in the field could be
reproduced in the laboratory. Second, the effects of prolonged sprays
or
repeated exposures were not studied. Third, all of the subjects were
cadets
at the local police academy and were generally healthy. Fourth, the
study
did not investigate the long-term effects of OC exposure or the potential
for complications from chronic occupational exposure to OC.
Target audience: Law enforcement policymakers and practitioners,
defense and prosecution attorneys involved in OC spray criminal and
civil
litigation, and medical examiners.
------------------------------
Pepper Spray's Effects on a Suspect's Ability to Breathe
By Theodore C. Chan, Gary M. Vilke, Jack Clausen, Richard Clark, Paul
Schmidt, Thomas Snowden, and Tom Neuman
Most law enforcement agencies in the United States have authorized
the
use of oleoresin capsicum (OC), or pepper spray, as a use-of-force
option
to subdue and control dangerous, combative, or violent subjects in
the
field. OC, with its ability to temporarily incapacitate subjects,
has been
credited with decreasing injuries among officers and arrestees by
reducing
the need for more severe force options.
Despite the success of OC spray, there is growing concern about its
safety,
particularly when exposure is combined with positional restraint.
A
number of arrestees exposed to OC, which induces coughing, gagging,
and
shortness of breath, have died in custody--thus prompting the allegation
that OC inhalation places individuals at risk for potentially fatal
respiratory compromise.[1]
The National Institute of Justice (NIJ), in conjunction with the Office
of
Community Oriented Policing Services (COPS), supported a study by
medical researchers at the University of California-San Diego to examine
the combined effects of OC exposure and positional restraint on
respiratory and pulmonary function among 34 volunteer subjects recruited
from a law enforcement training academy.
Research findings suggested that inhalation of OC spray does not pose
a
significant risk to subjects in terms of respiratory and pulmonary
function,
even when it occurs with positional restraint. However, OC exposure
did
result in a small but statistically significant increase in blood
pressure, the
origin of which remains unclear.
What is OC spray?
Oleoresin capsicum is the oily extract of the cayenne pepper plant.
Exposure to OC irritates the skin, eyes, and mucous membranes of the
upper respiratory tract. These properties of the pepper plant have
been
known for centuries. In Japan, samurai warriors threw rice-paper bags
filled with pepper extracts at the eyes of their enemies to cause
temporary
blindness. Chinese soldiers heated red peppers in hot oil to form
an irritant
smoke to be blown over enemy lines.
In 1973, OC became available as an aerosol spray and was initially
used
by FBI personnel and U.S. mail carriers to incapacitate humans and
animals on a temporary basis. During the late 1980s, it was widely
adopted by law enforcement agencies nationwide and was made available
for use by the general public. Currently, hand-held canister spray
models
are produced and used in this country. These models produce an aerosol,
liquid stream, or foam spray, with OC concentrations ranging from
1 to 10
percent. Pepper sprays are generally regarded as immediately effective,
safer, and less toxic than other classic forms of tear gas or mace,
such as
chloroacetophenone (CN) or o-chlorobenzyildene malononitrile (CS).
About this study
Previous studies have examined the cough-inducing properties of
capsaicin (the active ingredient of OC) spray, and a few have looked
at the
health effects of OC in humans. In addition, some research has been
conducted to determine if prone maximal restraint (the "hogtie"
or
"hobble" position) may lead to positional asphyxia (death
caused by
obstructed airways or other interference with breathing resulting
from
body position).
The study discussed in this Research in Brief is the first to investigate
whether OC exposure by itself or in combination with positional restraint
resulted in respiratory compromise that could put individuals at risk
for
significant injury or death. The study also examined the effects of
OC
spray/positional restraint on blood pressure and explored whether
the
health effects associated with OC exposure might be influenced by--
o Body weight and size.
o Asthma or other pulmonary disease.
o The use of respiratory inhaler medication.
o A history of smoking.
Study subjects
Thirty-seven individuals (training staff and cadets) from the San
Diego
Regional Public Training Institute were recruited and enrolled as
subjects
for the study. Two subjects were excluded at the outset: One had fractured
his ribs and was unable to adequately perform pulmonary function testing;
the other had a fractured arm immobilized in a cast, making it impossible
to place him in the restraint position. A third subject was excluded
after
fainting when his blood was drawn in the first trial. He had been
exposed
to the placebo spray in the sitting position but was never exposed
to OC
spray or restrained at any time.
Overall, 34 subjects (24 men and 10 women) completed the study. The
average age was 31.7 years, with subjects ranging from 22 to 46 years.
The average weight was 79.1 kilograms (about 174 pounds), with subjects
ranging from 52 to 107 kilograms (approximately 115 to 236 pounds).
Seven subjects were classified as overweight (with a body mass index,
or
BMI, of more than 28 kg/m2), and eight subjects had a history of smoking,
lung disease, or respiratory inhaler medication use.
Study design
A randomized, crossover, controlled laboratory study on human subjects
was performed, comparing the effects of OC spray and a placebo spray
followed by the sitting and restraint positions. The 34 subjects completed
136 separate trials (4 trials per subject) of varying exposure and
position
such that each served as his or her own control. Eight trials were
excluded
from analysis because the subject did not adequately inhale when exposed
to OC spray. As a result, 128 separate trials were analyzed for the
purposes of this study.
For the spirometric and pulmonary function testing data, an additional
four
trials were excluded from the testing because it did not meet American
Thoracic Society criteria for reproducibility and variability.[2]
An
additional two trials were excluded from the findings on arterial
blood gas
data because venous rather than arterial blood was sampled; one trial
was
excluded from the findings on blood pressure data due to mechanical
instrument error.
Study findings
Sitting position. Researchers found no evidence that OC spray inhalation
and exposure resulted in any respiratory compromise in the sitting
position. Statistically, there was no significant difference in percent
of
predicted values for FVC (forced vital capacity--the amount of air
that can
be expelled from the lungs after a maximal inspiration) or FEV1 (the
amount of air that a subject can forcibly expel in 1 second during
a forced
expiration test) between the OC and placebo groups at 1.5 and 10 minutes
after exposure. Clinically, values remained within the normal range
at 1.5
and 10 minutes after OC exposure and inhalation (see exhibits 1 and
2).
OC spray exposure did not result in any statistically significant
differences
in blood oxygenation when compared with placebo in the sitting position.
Blood oxygenation remained at clinically normal levels (see exhibit
3) and
carbon dioxide levels decreased after exposure to OC spray. This small
but
significant finding suggests that ventilation actually increased after
OC
exposure (see exhibit 4).
Restraint position. The findings of this study concerning the restraint
position are consistent with the authors' previous studies on respiratory
function and restraint, which found that restraint led to declines
in FVC
and FEV1 but found no evidence of hypoxemia (low levels of blood
oxygenation), hypercapnia (increased carbon dioxide levels), or
hypoventilation (decreased ventilation of the lungs).[3]
In this study, researchers found no evidence that OC exposure resulted
in
any additional change in respiratory function in the restraint position.
In
both the OC and placebo groups, pulmonary function was restricted
in the
restraint position, but measurements remained within the normal range.
Moreover, there were no statistical differences between the OC and
placebo groups relative to these declines (see exhibits 1 and 2).
Just as in the sitting position, there was no difference in oxygenation
in the
restraint position between the OC and placebo groups (see exhibit
3).
There was also no difference in carbon dioxide levels between the
two
groups in the restraint position, suggesting that OC exposure had
no
adverse effect on ventilatory function in restrained subjects (see
exhibit 4).
Thus, OC inhalation had no effect on the pulmonary function changes,
oxygenation, or ventilation associated with restraint.
Cardiovascular effects. Exposure to OC spray resulted in a small increase
in heart rate when compared with placebo. While statistically significant,
this difference is probably of no clinical importance, since average
heart
rates for all groups (regardless of exposure or position) remained
well
within normal limits (see exhibit 5).
Mean arterial blood pressure, however, was significantly elevated
after
exposure to OC spray when compared to placebo in both the sitting
and
restraint positions. This difference, though small, persisted at 3,
6, and 9
minutes after exposure (see exhibit 6). The reasons for this remain
uncertain and may simply be related to the discomfort and pain associated
with OC exposure.
Effects of body size and weight. Researchers found no evidence of
additional restrictive pulmonary dysfunction in seven overweight subjects
in the sitting or even the restraint position with OC or placebo exposure.
In
this group, OC exposure did not lead to hypoxemia or hypoventilation
in
either the sitting or restraint position and actually seemed to improve
oxygenation in the sitting position. Clearly, however, these conclusions
must be tempered by the small size of this subgroup and the fact that
none
of the subjects were morbidly obese (BMI greater than 32 kg/square
m).
Asthma, smoking, respiratory inhaler medication use. Researchers found
no evidence that OC spray inhalation and exposure resulted in respiratory
compromise in subjects with a history of lung disease, asthma, smoking,
or respiratory inhaler medication use. In this subgroup, OC exposure
had
no effect on pulmonary function in the sitting or restraint positions.
There
was also no evidence of hypoxemia, hypercapnia, or hypoventilation
after
OC inhalation for this group in either the sitting or restraint positions.
Yet
while these results suggest that OC exposure does not result in respiratory
dysfunction in those with potential respiratory abnormalities, it
is
important to note that this study cannot make definitive conclusions
due to
the small number of subjects (eight) in this subgroup.
Study caveats and implications
Limitations of this study. This study was performed on human subjects
in
a clinical laboratory and did not attempt to replicate all the conditions
that
may be encountered in the field. Field subjects are often in a state
of
extreme agitation and "excited delirium" as a result of
underlying
psychiatric disease or intoxication from recreational drugs. Subjects
are
often involved in violent physical struggles before, during, and after
the
use of OC spray or positional restraint. There has been speculation
that
subjects in the field undergo extreme levels of exertion leading to
exhaustion that may affect pulmonary function. Although previous studies
have attempted to replicate exertion and struggle, it is unlikely
that all
conditions that occur in the field--particularly the physiological
and
psychological effects of stress and trauma-- can be reproduced in
the
laboratory.
Moreover, as this study focused on inhalation exposure, all subjects
wore
goggles to reduce OC exposure to the eyes, which causes irritation
and
pain. Ocular OC exposure may exacerbate the physiological stress of
field
subjects but was not assessed in this study. In addition, restrained
subjects
were placed on a medical examination table rather than on a hard surface,
as often occurs in field settings.
This study attempted to replicate OC exposure in the field as much
as
possible in the laboratory setting. In doing so, exact capsaicin dosing
was
not standardized. Rather, subjects, whose heads were placed in a 5'
x 3' x
5' exposure box, received a standard 1-second spray directed from
5 feet
away as dictated by both manufacturer recommendations and local police
policies regarding the use of OC. Spraying from less than 5 feet away
does
not allow for adequate aerosolization of OC and is likely to reduce
the
amount of inhalation exposure.
Exposure in the box was limited to 5 seconds while in the laboratory.
Although this may seem to be a short period of time, spray in the
field
usually occurs in an open setting where OC dissipates rapidly. Moreover,
by containing the spray within the exposure box, it is likely that
subjects
were exposed to a much higher concentration of capsaicin than might
occur in the open air.
This study did not examine repeated OC spray exposures, which
commonly occur in the field setting. Researchers used an aerosol form
of
OC spray, rather than the liquid or foam forms that are also used
by law
enforcement agencies, because the aerosol form was more likely to
be
inhaled than other forms and was thus more appropriate for a study
on the
respiratory effects of OC.
Although subjects were monitored carefully for 1 hour after each trial
and
were checked by the research staff for significant adverse reactions,
they
were not assessed for any delayed or long-term effects from exposure.
Moreover, this study did not address issues regarding the potential
for
long-term complications from chronic occupational exposure to OC.
Finally, it is important to emphasize the limited nature of the additional
analyses performed on the subgroups of subjects who were overweight
or
had potential respiratory abnormalities. These groups were small in
number and the analysis in this study lacked sufficient statistical
power to
make any definite conclusive findings.
Law enforcement implications. Study findings support the contention
that
OC spray inhalation, even when combined with positional restraint,
poses
no significant risk to subjects in terms of respiratory and pulmonary
function. Although capsaicin spray has been studied extensively, this
study
assessed pulmonary and respiratory function after exposure to a
commercially available OC spray used by law enforcement agencies
nationwide. OC exposure produced no evidence of pulmonary
dysfunction, hypoxemia, or hypoventilation in either the sitting or
restraint
positions. These findings also applied to the groups of overweight
subjects
and to those with potential respiratory abnormalities. On the issue
of
in-custody deaths, this study indicates that OC inhalation and exposure
do
not cause significant respiratory injury and should not lead to an
increased
risk of respiratory compromise, arrest, or death--thus lending credence
to
the large retrospective field studies that have found little evidence
that OC
causes significant respiratory injury.
These findings will aid law enforcement agencies by providing data
supporting the safety of OC spray, even when used in combination with
positional restraint. First, they will provide law enforcement personnel
some measure of comfort in the knowledge that they are employing force
methods that have been tested and found safe in humans in clinical
studies.
They may improve the relationship between local agencies and their
communities, as the general public will be aware that officers in
their
communities are employing force methods that have been rigorously
studied in a clinical laboratory on human subjects. Questions regarding
OC use in cases of custody death will be less likely to contribute
to the
public controversy and contentiousness that often follow these cases.
Second, this study will aid law enforcement agencies when facing
accusations of excessive force based on the unfounded contention that
OC
exposure results in respiratory compromise. Study data will assist
law
enforcement agencies in deterring and defending themselves from
litigation that can have a negative impact on the well-being and morale
of
their agencies, and, more directly, on their personnel and field officers.
Third, on a general public policy level, this study provides solid
scientific
evidence that can be used in the search for safer methods of restraint.
In
the past, controversy regarding police force methods and restraint
has been
based on anecdotal evidence and case reports, rather than the scientific
study of human physiology. While many other controversies remain,
such
as the impact of physiological and psychological stress, external
weight
compression during restraint, and the cardiovascular effects of stress
and
restraint, this study provides a physiological and scientific basis
from
which to investigate and assess law enforcement force methods and
custody restraint procedures.
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