It is a classic action-movie scenario. At the climax of the story, our hero must infiltrate the villain’s lair, which is guarded by a small army of gun-wielding henchmen. But despite being gifted with the obligatory perfect aim and bottomless magazines, for one reason or another our hero can’t simply charge in guns blazing. Perhaps this is a stealth mission, and gunfire would attract too much attention. Or perhaps like MacGyver or Batman our hero has an aversion to guns or tries to avoid killing as much as possible. Whatever the case, thankfully they have plenty of options for simply knocking out the henchmen. They could shoot them with a tranquilizer dart, or come in closer to administer chloroform or knock-out gas. Or if all else fails, there’s always the good old-fashioned knockout blow to the head. Equally fortunate for our hero, the villain also doesn’t like to kill – at least not right away. He would rather capture our hero alive and subject them to a more elaborate and exotic death involving giant lasers or a tank full of sharks. And so in the course of the battle our hero is struck over the head and knocked unconscious, only to come to a few hours later – a bit dazed, but otherwise fully alert and ready to make their daring escape and finally defeat the villain.

…only no, no they wouldn’t – at least not in real life. More likely they would wake up with an incapacitating headache, a severe concussion, or not even wake up at all. For sadly for all you would-be action heroes out there, rendering someone unconscious is a far more complicated – and dangerous – business than Hollywood would have you believe.

Starting with the classic knockout blow to the head, while athletes like boxers are knocked unconscious all the time, the mechanics and effects of such knockouts are very different from what is typically portrayed in movies. Firstly, most boxing knockouts are inflicted not by a single massive punch but by a series of punches whose cumulative effect ultimately results in unconsciousness. The moment of unconsciousness is usually preceded by a progressive loss of motor coordination starting in the feet, as Anthony Alessi, a ringside physician for the Connecticut State Boxing Commission, explains:

“They become flat-footed, which is the inability to adjust. Boxers can’t move forward or backward quickly. As you watch their feet, you realize that the same lack of coordination is going on in their upper extremities in their hands. And eventually they are unable to defend themselves.”

Secondly, in most movies people are rendered unconscious by a blow to the back or top of the head, often with a beer bottle, vase, or other breakable object. In reality, such blows rarely result in unconsciousness, for the key to a successful knockout is imparting sufficient acceleration to the head. This acceleration is in turn transferred to the brain, which collides with the inside of the skull, inflicting trauma that results in a knockout. The ideal means of imparting such acceleration is to strike at the chin, causing the head and the brain to snap back violently. Even more effective is a blow to the side of the head, which imparts rotational acceleration to the brain. While in the former case the brain is somewhat protected by the cerebrospinal fluid in which it is suspended, this fluid offers no protection against rotation, meaning that it takes less force to knock someone out with a roundhouse punch than with an uppercut.

The exact mechanism by which a knockout blow induces unconsciousness is still poorly understood, but one leading theory posits that trauma to the brain causes microscopic pores to form in the cell membranes of neurons- a process known as mechanoporation. These pores allow potassium ions to leak out of the neurons and calcium ions to flow in, depolarizing the cell. Restoring this electrolyte balance requires massive amounts of blood and energy, and when demand exceeds supply, the brain momentarily shuts itself down in order to conserve energy. And the key word here is momentarily; unlike in the movies where a knocked-out person remains unconscious for hours, allowing the henchmen to bundle the hero into a waiting car trunk and spirit them away to the villain’s lair, real-life knockouts typically last no longer than a few minutes. If unconsciousness persists for longer, this is typically a sign that something has gone very, very wrong. The person may be suffering from a severe concussion or cerebral haemorrhaging, both of which can result in severe long-term health effects including coma, permanent brain damage, or even death. Indeed, studies have shown that around 90% of professional boxers will endure some form of brain injury over the course of their careers, while 15-40 will suffer permanent, chronic brain damage. Thus, if our hero remains unconscious for hours on end, it is highly unlikely they will awake to find themselves fit and ready to fight.

A somewhat safer method of rendering someone unconscious is to go for the jugular – or, more accurately, the carotid artery. This can be done in a number of ways, including the classic “sleeper” hold. This maneuver applies pressure to the carotid arteries, cutting off blood flow to the brain and resulting in unconsciousness within 10-20 seconds. An even more dramatic technique is the carotid strike or “Okinawan slap”, taught in several martial arts including karate and taekwondo. This consists of a sharp blow to the carotid sinus, the junction in the neck where the common carotid artery branches into the internal and external carotid. This area contains numerous baroreceptor nerves which serve to detect and regulate changes in blood pressure. The carotid strike fools these receptors into thinking that the victim’s blood pressure is too high, triggering a massive drop in blood pressure that temporarily starves the brain of oxygen, leading to immediate unconsciousness. But while certainly dramatic enough for the silver screen, as with a knockout blow the effects of the sleeper hold or carotid strike are short-lived, with unconsciousness lasting only a few minutes at most. These techniques also come with their own severe health risks, including accidental strangulation, dislodging blood clots, and accidental stimulation of the glossopharyngeal nerve resulting in cardiac arrest.

Alright, so physically knocking someone out is too risky for our morally-upright hero or our gloating-obsessed villain. But what about a chemical knockout, like the knockout gas so widely favoured by the villains of the 1960s Batman TV series? Alas, despite what Hollywood would have us believe, pharmacologically-induced unconsciousness is in many ways even more fraught than the good old-fashioned knockout blow.

A classic knockout method of the detective genre is to soak a rag in ether or chloroform and hold it over the victim’s mouth and nose. This apparently results in near-instant unconsciousness that lasts for hours, allowing our dastardly villain’s henchmen to easily spirit away the unsuspecting damsel in distress. But while ether and chloroform can indeed induce unconsciousness and were used for over a hundred years as surgical anaesthetics, the real-life effects of these chemicals are nowhere near as quick – or tidy – as their fictional counterparts.

Diethyl ether was first prepared in 1540 by Prussian Botanist Valerius Cordus, who immediately noted that inhaling its vapours produced a powerful feeling of euphoria and unconsciousness at higher doses. Over the next 300 years the chemical was widely used as a recreational drug, drunk mainly by the lower classes as a substitute for alcohol. Starting in the late 18th and early 19th Centuries it also became popular among upper-class students, who consumed it at raucous“ether frolics” along with another recently-discovered euphoric substance: nitrous oxide, better known as laughing gas. It was at one such party in 1844 that American dentist Horace Wells observed a curious phenomenon. While intoxicated on nitrous oxide, one attendee struck his leg on a wooden bench but appeared to feel no pain. Realizing that nitrous oxide might hold the key to eliminating the pain of tooth extraction and other surgical procedures, Wells embarked upon a series of experiments culminating in a public demonstration at the Massachusetts General Hospital in Boston on January 20, 1845. Unfortunately for Wells, the gas was improperly administered, and when he attempted to extract a tooth his patient cried out in pain, causing the audience of medical students to storm out shouting “humbug.” While Wells’s career never recovered from this incident, one attendee, a fellow dentist named William Morton, was inspired by the demonstration and set off in search of a better anaesthetic gas. He settled on Diethyl Ether after accidentally leaving a bottle open in his study and being knocked unconscious by the fumes. Further experimentation revealed just how useful and versatile ether was as an anaesthetic. Being a liquid it was more readily transportable, and could easily be administered by placing a cloth or a gauze-lined mask over the patient’s nose and dripping the ether onto it. Even better, the effective dose of ether was relatively low, meaning that the patient lost consciousness before dangerous levels could accumulate in the blood and did not risk being asphyxiated as with inhaling nitrous oxide. On October 16, 1846, Morton conduced a historic demonstration at Massachusetts General Hospital in an amphitheatre now known as the “Ether Dome.” Once the patient, Mr. Gilbert Abbot, was sedated with ether, surgeon Dr. John Warren proceeded to remove a tumour from his neck. Though ether had first been used as a general anaesthetic four years earlier by Georgia physician Dr. Crawford Long, Morton’s demonstration brought the practice into the mainstream, and for nearly 100 years Diethyl Ether would remain the surgical anaesthetic of choice until the introduction of more modern inhalants like halothane in the 1950s.

But ether was not without its drawbacks. For one thing it was highly volatile and flammable, resulting in numerous explosive operating room accidents. It also produced a number of unpleasant side effects, such as irritation of the mucous membranes, profuse salivation, and violent postoperative nausea. Thus, in 1847 Scottish physician Sir James Young Simpson began experimenting with an alternative anaesthetic: chloroform. A clear, sweet-smelling liquid, chloroform was non-flammable and induced unconsciousness more quickly, for longer periods, and at lower doses than ether. After being famously administered to Queen Victoria in 1853 during the birth of her eighth child, Prince Leopold, use of chloroform in medicine exploded, the drug remaining in common use until the 1930s.

Yet despite the proven track record of ether and chloroform as surgical anaesthetics, they are hardly the tools of choice for a would-be kidnapper. For one thing, the effects of these substances are far from instantaneous; indeed, it can take up to 20-30 minutes of deeply breathing in ether or chloroform fumes for unconsciousness to set in – a procedure requiring a tad more cooperation than the average kidnap victim is likely to display. At high doses ether can also irritate the lungs and throat, leading to violent coughing and spasms that make further inhalation and absorption difficult. Even worse, while ether is relatively safe even at high doses, the therapeutic index of chloroform – that is, the difference between an effective dose and an overdose – is very narrow, creating a high risk of accidental overdose. As chloroform is a respiratory and cardiac depressant, such an overdose can lead to cessation of breathing, cardiac arrest, and ultimately death. Furthermore, the dosage required to induce unconsciousness or an overdose vary widely from person to person, being affected by factors as diverse as age, sex, body mass, and overall fitness. Indeed, the difficulty of administering the correct dose to safely induce unconsciousness is precisely why the specialized field of anaesthesiology exists in the first place.

A dramatic demonstration of the effects of improper dosage took place on October 23, 2002 when 40 Chechen terrorists took over the Dubrovka Theatre in Moscow and held 850 patrons hostage. During the ensuing siege, Russian Spetsnaz special forces troops pumped an anaesthetic gas into the theatre’s ventilation system to incapacitate the terrorists prior to storming the building. But while the raid succeeded in killing all 40 terrorists, the gas dosage proved too high, resulting in the deaths of 115 of the 117 hostages killed in the siege and a further 400 hostages being hospitalized. While the Russian government has never officially revealed the identity of the gas used, experts speculate that it might have been an aerosolized hallucinogen known as BZ or QNB, or a derivative of the powerful opioid fentanyl such as carfentanyl. Whatever the case, the tragedy of the Moscow Theatre Siege clearly demonstrates that while gauging the correct dose of anaesthetic in a controlled medical environment is difficult, in an uncontrolled environment it is nearly impossible.

The problem of dosage also applies to that other favourite knockout-delivery system: the tranquilizer dart. When used on animals, the dosage of tranquilizer darts must be carefully matched to the target’s body mass and metabolism in order to a) ensure the dart actually knocks the animal out, and b) prevent an overdose. Most common tranquilizing drugs like sodium thiopental and azaperone are powerful respiratory depressants, meaning that upon being tranquilized animals must be closely monitored by veterinarians to ensure that they do not suddenly stop breathing. As our intrepid hero is likely to encounter henchmen of all shapes and sizes, using a one-size-fits-all tranquilizer dart dose is likely to result in either a whole lot of groggy but still-conscious henchmen or a whole lot of dead ones. Furthermore, as with inhaled anaesthetics, the effects of injected tranquilizers are not instantaneous. Even the most powerful drugs require a few minutes to circulate through the bloodstream and take effect – more than enough time for a henchman to return fire or at least sound the alarm. And this is assuming a best-case scenario wherein the drug is injected directly into the bloodstream; a random tranquilizer dart hit is more likely to result in an intramuscular injection, which will take even longer to take effect.

But what about slipping something into someone’s drink, the signature move of many a fictional femme fatale? This practice is popularly known as “slipping a Mickey Finn” after one Michael “Mickey” Finn, the infamous 19th Century proprietor of Chicago’s Lone Star Saloon who was alleged to have drugged his patron’s drinks before robbing them. Finn’s drug of choice – and that of many a spy and detective fiction writer thereafter – was chloral hydrate, a sedative and hypnotic once widely used in psychiatric hospitals due to its low cost and still occasionally used today for sedating children and treating insomnia. But once again, as with injected or inhaled sedatives, the effects of chloral hydrate are nowhere near as instantaneous as depicted in the movies; depending on dosage, it can take anywhere from 20-60 minutes for unconsciousness to set in. And like chloroform, the therapeutic index of chloral hydrate is extremely narrow, with overdose occurring at doses as low as 600 milligrams. Lower doses can induce a variety of unpleasant side effects including nausea, vomiting, confusion, convulsions, irregular breathing, and cardiac arrhythmia; while higher doses can lead to coma, respiratory arrest, and death. Not necessarily an issue if you are trying to rob saloon patrons, but something of a problem if you are trying to safely knock out and kidnap someone.

In conclusion, despite Hollywood’s frequent assertions to the contrary, a quick, reliable, and safe way to render someone unconscious for long periods of time is a lot harder to achieve than they depict. The brain is a surprisingly resilient organ, and any injury or chemical capable of shutting it down – even temporarily – is likely to inflict further, more serious damage. Thus, as we’ve likely shouted dozens of times at overly-righteous heroes or monologuing villains, sometimes it’s easier to just shoot the bastard.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

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