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Emergency Medicine News:
doi: 10.1097/01.EEM.0000411479.67113.e5
InFocus

InFocus: The Physiology of TASERs

Roberts, James R. MD

Free Access

Emergency physicians are on the frontline when dealing with somewhat gnarly and always irate individuals who have had a recent unplanned introduction to a TASER. These encounters are fraught with highly charged social and racial issues, and usually are peppered with insinuations of police brutality.

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The pertinent issues of excited delirium and the use of the TASER were highlighted in past issues of EMN. (See FastLinks.) Basic concerns are that the TASER is detrimental to one's health, and is somehow contributory to sudden death when someone is unceremoniously subdued after misbehaving under police scrutiny.

Numerous attempts have been made to clarify the exact pathophysiology of humans versus TASER. But in the minds of many, especially in the lay press, the device has been pronounced guilty until proven innocent. It's difficult for the general public to believe that a violent encounter with police did not electrocute their loved one. When there is an untoward medical event after tasering, good luck trying to convince the outraged nonscientist that the TASER wasn't culprit.

Unraveling the exact science behind the TASER is still in its nascent stages. But, all in all, the TASER appears to be a remarkable device that has enamored law enforcement, bewildered the general public, terrified potential felons, provided salacious fodder for the prime-time national media, piqued the interest of the legal profession, and outraged human rights organizations. For an absolutely superb review of the TASER, aficionados should read the book by Kroll and Ho. (TASER Conducted Electrical Weapons: Physiology, Pathology, and the Law (New York: Springer; 2009.)

This month's column will review some of the recent data aimed at demystifying alleged TASER-induced pathology.

Physiological Effects of Conducted Electrical Weapons on Human Subjects

Vilke G, Sloane CM, et al

Ann Emerg Med

2007;50(5):569

Although the TASER is touted to have been used on more than 150,000 volunteers (as of 2007) and in more than 100,000 real-life police confrontations, formal studies evaluating the physiological effects of the oft-maligned device are sparse. These authors — along with other emergency medicine colleagues, Drs. Jeffrey Ho, Donald Dawes, and William Bozeman — are the leading researchers in this area. The researchers somehow convinced 32 healthy law enforcement officers to receive a standard five-second TASER electrical discharge to evaluate its effects on normal human subjects and to define and ferret out potential pernicious physiological stress from the stun gun.

When discharged, the TASER automatically delivers an electrical pulse for five seconds, requiring conscious action (a trigger pull) by the user to deliver additional discharges. The TASER delivers its potent electrical impulse up to 30 feet away via barbed wires from a battery-operated gun that causes incapacitating tetanic muscular contractions and sudden disabling of the tasered individual.

While this study was unable to determine the safety profile of the TASER in individuals with excited delirium, acidosis, those revved up by stimulants and hallucinogens, those on prescription medications, or those with clandestine heart disease, the data gained from this controlled study help unravel at least a modicum of TASER-related physiology.

Background: Somewhat dubious reports of deaths have been described following TASER administration. Amnesty International has reported more than 150 purported TASER-related deaths since 2001, and the Arizona Republic reports more than 160 cases of deaths following stun gun use. The science behind such accusations is literally nonexistent, however, and an ostensible cause-effect hinges largely on circumstantial evidence.

It is generally admitted that the vast majority of reported deaths secondary to TASER exposure do not include normal citizens minding their own business, but instead are the hapless individuals who are violent and obstreperous to the point of being a danger to themselves and others, often under the gargantuan influence of highly potent illegal drugs, such as cocaine, methamphetamine, or PCP.

Many cases involved those exhibiting blatant excited delirium, a process that can itself be fatal to even healthy young people. If one examines the actual incidents, drugs, delirium, violent threatening, Herculean struggling, and physical restraint are almost always lurking in the background, so many scientists have speculated that TASER deployment is only circumstantially related to the fatal outcome. Excited delirium has only recently been recognized as a distinct, potentially lethal syndrome, a true medical emergency replete with many nasty consequences. (See FastLinks for references.)

Some would argue that incapacitating a patient with a TASER is actually life-saving because it stops the downward spiral of struggling to exhaustion, acidosis, hyperthermia, and cardiorespiratory depression. It may also keep you from being shot. In the few case reports that indict the TASER, cardiac arrest is a delayed phenomenon, recognized many minutes following discharge.

If a lethal arrhythmia, particularly ventricular fibrillation, were the cause of death, one would expect it would manifest itself immediately. Because such documentation is lacking, many who take the time to investigate the facts believe the TASER cannot cause VF or other significant physiological aberrations. A common explanation: the underlying physiology that prompted tasering in the first place may be the sole etiology of sudden death.

The Study: Recruits, as part of their police training, were studied for evidence of physiologic stress after exposure to the standard TASER X26 during and following a brief five-second jolt. Subjects were men and women between 18 and 60. All were screened to rule out underlying overt medical pathology. Darts from the TASER were shot into the subject's back from two to three meters with the darts centered on the subject's back between the shoulder blades. One criticism of this study could be that the current from the darts did not actually transverse the heart.

Following the TASER discharge, patients were monitored up to an hour for respiratory rate, tidal volume, and end-tidal PC02. Baseline and post-TASER EKGs were taken. Blood was analyzed for electrolytes, blood gases, lactate, and troponin levels.

The investigators did find some statistically significant differences, primarily clinically irrelevant elevation of systolic blood pressure. The highest blood pressure was 140 mm Hg, returning to baseline within 10 minutes. Pulse rate and diastolic pressure were not adversely affected. No significant alterations in oxygen saturation were found.

The TASER activation did increase minute ventilation, tidal volume, and respiratory rate immediately after activation, but minimally so, and all measures returned to normal at 10 minutes, and remained there. No evidence of hypoxemia or hypoventilation was seen.

Minor changes were found in bicarbonate and lactate concentrations, thought to be due to muscular activity, but they also returned to baseline during this study period. Troponin levels were normal. No subject had EKG evidence of ischemia. This study, in healthy subjects, found no clinically relevant changes in ventilation, acid- base status, electrolyte concentrations, troponin, or EKG following the five-second exposure to the standard TASER X26.

COMMENT: These subjects were healthy and drug-free without known cardiac-metabolic-respiratory perturbations and without agitation or mental status changes. In this somewhat artificial milieu, TASER activation was brief, and did not exceed a single five-second activation. In the field, subjects often receive multiple shocks. As with other studies, these investigators were unable to detect any induced electrical dysrhythmia or direct cellular damage related to TASER exposure. The mean pH remained between 7.42 and 7.45, negating the concept that brief TASER use causes a severe metabolic acidosis.

It must be a rather shocking experience to be tasered, and everyone would find it extremely unpleasant. Admittedly, the public in general is quite afraid of electricity, but at least in this study, the TASER did not electrocute anyone or cause any measurable harm. If I had to choose between a TASER and a police firearm, I would opt for the TASER hands down. Most individuals who are tasered are so severely agitated that physical restraint, mace, or multiple blows from a nightstick will not persuade them to behave or stop trying to kill the police officer or paramedic.

Verbal de-escalation is a waste of time and an opportunity for more mayhem. The electrical discharge from a TASER, however, really gets one's attention, and it quickly ameliorates the aggressiveness and physical prowess of even the most formidable opponent.

Absence of Electrocardiographic Changes after Prolonged Application of the Conducted Electrical Weapons in Physically Exhausted Adults

Ho J, Dawes DM, et al

J Emerg Med

2011;41(5):466

This recent article by well-known investigators of TASER physiology advances the previous study by deploying the TASER on physically exhausted individuals, similar to those real-life subjects who tangle with a police TASER. The subject's median age was 39 (range 35-45), and four volunteers had medical problems, including hypertension, glaucoma, pituitary adenoma, and asthma. At least one subject was taking an ACE inhibitor, a statin, a beta agonist, or an inhaled steroid. As a nice warm touch, the investigators gave each of the volunteers their own TASER upon successful completion of the study.

Following a medical evaluation that demonstrated a normal healthy individual, the subjects performed a series of intense vigorous activities to invoke anaerobic metabolism. This included pushups and running on a treadmill until they claimed exhaustion. The level of exhaustion was measured by venous pH (average 7.22). Prior work by the authors demonstrated that prolonged TASER use on exhausted humans does not worsen markers of acidosis. (Am J Emerg Med 2009;27[4]:413.)

Instead of firing a TASER, the electrodes were manually placed on the sides of the chest so electivity transversed the heart. Simulating field conditions, a standard police-issued TASER X26 was discharged continuously for 15 seconds. Note that the prior study only used a five-second discharge. After TASER exposure, all 25 EKGs were interpreted as normal, including one that had demonstrated PVCs prior to enrollment.

This protocol was a reasonable simulation of the physiologic compromise present in agitated subjects who would be incapacitated by the TASER. The prolonged 15-second exposure as well as exercising to exhaustion was thought to better replicate field conditions.

This study supports the use of the TASER as a simple method of physical control to initiate stabilization and medical care in the well known prehospital setting where immediate de-escalation of violent activity is mandated. They point out that rapid TASER incapacitation for prolonged delirium may, in fact, be a life-saving process rather than a fatal intervention.

COMMENT: This is a nifty study, about as good as one gets in the l-ab. But the subjects did not have mental illness, intoxication, hypoglycemia, or extreme stimulant abuse, and they were not physically stressed for hours in 100-degree heat. They did not continue to exercise after the jolt, and acidosis was rather mild.

One wonders if an individual with Brugada syndrome, underlying cardiomyopathy, congenital heart disease, premature atherosclerosis, or aberrant coronary circulation would react differently. The authors do point out, however, that the volunteers they studied were not young, did not have an exceptional level of physical fitness, and demonstrated a wide age range. A few of their underlying medical problems required controlling medication, and most were overweight by standard measures, termed a realistic representation of real-life TASER use.

Despite the public's perception and suspect contentions by various nonmedical groups, lethal effects of the TASER have simply never been demonstrated to a reasonable degree of medical certainty. In fact, the TASER's use does not appear to be associated with significant cardiovascular, respiratory, and metabolic problems, even in those stressed to simulate at least mild excited delirium. To my analysis, when used appropriately, the benefits of the TASER greatly outweigh physical restraint, chokeholds, nightstick clubbing, hog-tying, prolonged prone struggling, mace or pepper spray, or the ultimate incapacitating device, a police officer's gun.

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Animal Model Studies

Lakkireddy et al studied the effect of the TASER in cocaine-toxic pigs. (J Am Coll Cardiol 2006;48[4]:805.) Their conclusion was that cocaine use actually decreases the likelihood of TASER-induced VF, and cocaine increases the safety margin of the TASER up to two times baseline. In the animal model, cocaine reduced vulnerability to TASER-induced VF. Histological damage to the heart by the applied charge was minimal, even after cumulative doses of more than 2000 times the standard TASER discharge. Seemingly, cocaine toxicity in the pig model provides a safety margin against potential TASER-induced cardiac arrhythmias.

In a simulated animal study, Dawes et al made sheep cardiotoxic with IV methamphetamine, then shocked the drugged animals with the standard police issue TASER X26. (Acad Emerg Med 2010;17[4]:436.) Animals were monitored while TASER electrodes directed current through the heart, with the shock lasting up to 40 seconds. In a few smaller sheep, the TASER did exacerbate some of the somewhat benign atrial and ventricular irritability (SVT, atrial, and ventricular ectopy) induced by methamphetamine toxicity. This was not seen in the larger sheep (up to 70 kg), however. Only sinus tachycardia was produced. No animal experienced lethal VF/VT.

The TASER output did not produce myocardial capture in the larger sheep as has been previously reported in other animal but not human studies. Myocardial capture is thought to be a potential arrhythmia-producing complication of the TASER. The authors acknowledge the limitations of animal models, and conclude that methamphetamine intoxication does not preclude the use of the TASER. These two animal studies will likely perturb Amnesty International, PETA, and the ACLU.

It should be duly noted that the vast majority of the research on the physiologic effects of the TASER has been supported or performed by the manufacturer, consultants to the manufacturer, or researchers with ties to law enforcement. I am astounded that vocal critics of the TASER have not funded research to prove their contentions rather than relying on speculation and emotion. Perhaps the extant researchers have a larger interest in finding the truth. The U.S. Department of Justice did conduct its own research. The results were similarly positive. (See table.)

Click and Connect! Access the links in this article by reading it on www.EM-News.com.

Reader Feedback: Readers are invited to ask specific questions and offer personal experiences, comments, or observations on InFocus topics. Literature references are appreciated. Pertinent responses will be published in a future issue. Please send comments to emn@lww.com. Dr. Roberts requests feedback on this month's column, especially personal experiences with successes, failures, and technique.

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U.S. Government Report on Effects of TASERs1

The U.S. Department of Justice recently released results of a TASER safety study completed in June 2009. The specific study is not readily available, but a summary of the work and editorial comments appeared in the May 2011 issue of the Forensic Drug Abuse Advisor.2

The researchers concluded that:

1. There is no apparent indication that respiratory function is significantly altered by a standard five-second X-26 TASER exposure, but that there was definitely some evidence of clinical effect, even if it was not significant.

2. There was no evidence of significant alteration in cardiac function nor was there any discernable damage to cardiac muscle or evidence of ischemia based on an evaluation of post-exposure changes in ECG and cardiac enzymes when measured from baseline.

3. Subjects appeared awake, alert, and able to function normally immediately after the TASER discharge ceased.

4. There was no evidence of cardiogenic shock-type symptoms such as syncope, dizziness, or altered mental status.

5. Serotonin levels were not significantly altered to a degree sufficient to induce Serotonin Syndrome, and levels of serotonin after exposure remained in a normal range.

6. The data analysis confirms the results of studies conducted by Ho et al3 (2006) and Vilke et al4 (2009) “that cardiac function is maintained during and after X-26 TASER exposure in healthy subjects.”

Forensic Drug Abuse Advisor Comment: “In this study, the heart was deliberately included in the discharge circuit of the device. In other words, the cardiac findings are even more convincing than earlier studies, and leave no question that the device does not induce either ventricular fibrillation or asystole.”

Note: TASERS are categorized as nonlethal weapons by the U.S. Department of Defense.

Dr. Roberts Comments: Remember, this was research sponsored and reviewed by the U.S. Department of Justice. It is always gratifying when new research confirms old results, but the design of this study was impeccable. This study also differed in one important respect from the studies of Ho and Vilke: The heart was deliberately included in the discharge circuit of the device. In other words, the cardiac findings are even more convincing than earlier studies, and leave no question that the device does not induce ventricular fibrillation or asystole.

1Performed at the Department of Biomedical Engineering at Texas A&M University. Principle Investigator: John Croscione, PhD, MD.

2Forensic Drug Abuse Advisor. Steven B. Karch, MD, FFFLM, Editor. May 2011; Volume 23; Issue 5. (www.fdaa.com). Reproduced with permission.

3Ho JD, et al. Acad Emerg Med 2006;13(6):589.

4Vilke GM, et al. Acad Emerg Med 2009;16(8):704.

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FastLinks

▪ Read Dr. Roberts' first article on TASERs and other EMN TASER coverage in a special collection, TASER/Excited Delirium Syndrome, on the EMN website at http://bit.ly/EMNTASER.

▪ The “Study of Deaths Following Electro Muscular Disruption: Interim Report” from the U.S. Department of Justice is available at http://1.usa.gov/DOJTASER.

▪ Read the American College of Emergency Physicians' “White Paper Report on Excited Delirium Syndrome” at http://bit.ly/ACEPExDs.

▪ Abstracts and full-text articles of studies cited by Dr. Roberts:

▪ Vilke GM, DeBard ML, et al. Excited Delirium Syndrome (ExDS): Defining Based on a Review of the Literature. J Emerg Med 2011 March 24 [Epub]: http://bit.ly/VilkeExDs.

▪ Vilke GM, Bozeman WP, Chan TC. “Emergency Department Evaluation after Conducted Energy Weapon Use: Review of the Literature for the Clinician.” J Emerg Med 2011;40(5):598: http://bit.ly/VilkeTASER.

▪ Vilke GM, Sloane CM, et al. “Physiologic Effects of the TASER after Exercise.” Acad Emerg Med 2009;16(8):704: http://bit.ly/VilkeExercise.

▪ DM Dawes, et al. “The respiratory, metabolic and neuroendocrine effects of a new generation electronic control device.” Forensic Science International 2011;207(1-3):55: http://bit.ly/DawesECD.

▪ Ho JD, Miner JR, et al. “Cardiovascular and Physiologic Effects of Conducted Electrical Weapon Discharge in Resting Adults.” Acad Emerg Med 2006;13(6):589: Full text available at http://bit.ly/vMLRIZ.

▪ Read all of Dr. Roberts' past columns in the EM-News.com archive.

▪ Comments about this article? Write to EMN at emn@lww.com.

© 2012 Lippincott Williams & Wilkins, Inc.

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